hv
photonics
Review
Semiconductor Nanomembrane-Based Light-Emitting
and Photodetecting Devices
Dong Liu 1 , Weidong Zhou 2 and Zhenqiang Ma 1, *
1
2
*
Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, WI 53706,
USA; dliu93@wisc.edu
Department of Electrical Engineering, University of Texas at Arlington, Arlington, TX 76019, USA;
wzhou@uta.edu
Correspondence: mazq@engr.wisc.edu; Tel.: +1-608-261-1095
Received: 1 June 2016; Accepted: 14 June 2016; Published: 17 June 2016
Abstract: Heterogeneous integration between silicon (Si), III-V group material and Germanium (Ge)
is highly desirable to achieve monolithic photonic circuits. Transfer-printing and stacking between
different semiconductor nanomembranes (NMs) enables more versatile combinations to realize
high-performance light-emitting and photodetecting devices. In this paper, lasers, including vertical
and edge-emitting structures, flexible light-emitting diode, photodetectors at visible and infrared
wavelengths, as well as flexible photodetectors, are reviewed to demonstrate that the transfer-printed
semiconductor nanomembrane stacked layers have a large variety of applications in integrated
optoelectronic systems.
Keywords: transfer printing; semiconductor nanomembrane; light-emitting diode; photodetectors;
flexible optoelectronics; silicon photonics
1. Introduction
The applications of semiconductor nanomembrane (NM) transfer technology both in electronic
and photonics have attracted intensive attention and research interests [1–24]. The basic concept
is instead of using the whole bulk material grown from substrate up to the functional layer, the
top functional membrane layer is released from its original substrate and transfer printed on a new
host. Pioneered by Rogers et al., a polydimethylsiloxane (PDMS) stamp-assisted transfer printing
process has been used to transfer a variety of crystalline semiconductor NMs on different foreign
host substrates. This heterogeneous materials stack could be integrated with Si and flexible substrate
applications [25–33].
The two most attractive characteristics of this semiconductor NM are: (1) flexibility, as the
semiconductor material is stretchable or bendable when in the form of thin layer (nanometers scale),
which is a highly desired mechanical property for flexible optoelectronic devices; (2) transferability
to a variety of foreign substrates, without the limitation by different materials’ growths condition
and lattice mismatch; heterogeneous integration could be formed between various combinations of
materials to serve a multi-functional and versatile purpose. Up to now, semiconductor NMs have been
successfully transferred onto numerous kinds of substrates, including glass [34–36], plastics [24–27],
biodegradable nanofibril paper [37], etc.
The transfer printing process basically consists of two main process: one is the release of crystalline
semiconductor NMs from the original growth substrate using selective etching; the other is transfer
printing onto the targeted substrate, as shown in Figure 1. During the selective etching step in
Figure 1a–c, the sacrificial layer underneath the desired NMs or strips is etched away, and still in the
etchant environment, the NMs fall on and bond with the substrate by a weak van der Waals force
(Figure 1d). Then, the NMs are ready to be picked up, and there are generally three approaches to
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transfer the NMs to a new host: (1) direct flip transfer; (2) stamp-assisted transfer; and (3) transfer
transfer the NMs to a new host: (1) direct flip transfer; (2) stamp-assisted transfer; and (3) transfer
printing without an adhesive layer, depicted in Figure 1e–g, respectively. For the former two
printing without an adhesive layer, depicted in Figure 1e–g, respectively. For the former two methods,
methods, an adhesive layer, such as SU-8, is necessary for the foreign substrate to be coated to
an adhesive layer, such as SU-8, is necessary for the foreign substrate to be coated to enhance
enhance the bonding strength. While for the one called dry transfer printing without an adhesive
thelayer,
bonding
strength. While for the one called dry transfer printing without an adhesive layer,
kinetically-controlled adhesion of the elastomeric stamp is employed to leave the NMs on the
kinetically-controlled
adhesion
of the elastomeric
stamp
is employed
to leave
NMs
the new
new host [14–17]. The
basic principle
is fast peeling
speed
during pick-up
andthe
slow
for on
releasing
host
[14–17]. The basic principle is fast peeling speed during pick-up and slow for releasing NMs.
NMs.
Figure
1. Generic
processofofa atransfer
transferprinting:
printing: (a,b)
(a,b) make
(SOI)
Figure
1. Generic
process
make aa pattern
patternon
onan
ansilicon
siliconononinsulator
insulator
(SOI)
wafer; (c) immerse in the etchant for the undercut; (d) the membrane layer gently falls down after the
wafer; (c) immerse in the etchant for the undercut; (d) the membrane layer gently falls down after the
buried oxide layer is completely removed; (e1) the adhesive layer-coated plastic substrate is flipped
buried oxide layer is completely removed; (e1) the adhesive layer-coated plastic substrate is flipped and
and the membranes picked; (e2) completion of the direct flip transfer; (f1) pick up the membranes by
the membranes picked; (e2) completion of the direct flip transfer; (f1) pick up the membranes by the
the elastomeric stamp; (f2) transfer printing on the adhesive layer-coated flexible substrate;
elastomeric stamp; (f2) transfer printing on the adhesive layer-coated flexible substrate; (f3) completion
(f3) completion of the stamp-assisted transfer; (g1) pick up the membranes with fast peeling speed;
of the stamp-assisted transfer; (g1) pick up the membranes with fast peeling speed; (g2) release the
(g2) release the membrane with slow peeling speed; (g3) application of an additional annealing
membrane with slow peeling speed; (g3) application of an additional annealing procedure to enhance
procedure to enhance the bonding force (reprinted from [18]).
the bonding force (reprinted from [18]).
In recent years, the impressive progress of NM transfer and stacked NMs in photonic
In recent years,
the implemented;
impressive progress
of NM
transfer
and
stacked NMs
in photonic
applications
applications
has been
one main
research
focus
is integrating
III-V
material or
efficient
material
silicon
substrate
silicon photonics
applications,
including
a vertical
haslight-absorbing
been implemented;
oneonto
main
research
focus for
is integrating
III-V material
or efficient
light-absorbing
cavity onto
laser silicon
with two
Si photonic
crystalphotonics
(PC) mirrors
[12], first-order
diffraction-based
surface
material
substrate
for silicon
applications,
including
a vertical cavity
laser
emitting
withcrystal
a Si PC(PC)
pattern
[30],[12],
an edge-emitting
laser on Si substrate
[38],
multi-color
with
two Silasers
photonic
mirrors
first-order diffraction-based
surface
emitting
lasers
photodetectors
[39]
and
cavity-enhanced
on multi-color
a silicon on
insulator (SOI)
with
a Si PC pattern
[30],
anaedge-emitting
laserGe
onphotodetector
Si substrate [38],
photodetectors
[39]
substrate
[40].
The
other
is
to
take
advantage
of
the
flexible
mechanical
property
to
realize
and a cavity-enhanced Ge photodetector on a silicon on insulator (SOI) substrate [40]. bendable
The other
phototransistors
and
[25,41–43] property
and light-emitting
(LEDs)
[44] by transfer
is to
take advantage
ofphotodetectors
the flexible mechanical
to realizediodes
bendable
phototransistors
and
printing
a
very
thin
membrane
layer
onto
a
plastic
substrate.
photodetectors [25,41–43] and light-emitting diodes (LEDs) [44] by transfer printing a very thin
membrane layer onto a plastic substrate.
2. Semiconductor NM-Based Light-Emitting Devices
2. Semiconductor
NM-Based
Light-Emitting
Devices materials (III-V group) and other substrates
Heterogeneous
integration
between light-emitting
(Si or flexible substrate) is highly demanded in applications, such as silicon photonics and flexible
Heterogeneous integration between light-emitting materials (III-V group) and other substrates
optoelectronic devices. Compared to wafer-bonding approaches, transfer printing is insensitive to
(Si or flexible substrate) is highly demanded in applications, such as silicon photonics and flexible
the wafer-size mismatch and more efficient by substrate reuse [14]. Moreover, the developments in
optoelectronic devices. Compared to wafer-bonding approaches, transfer printing is insensitive to the
transfer printing techniques have enabled a clean and atomically-smooth interface after the transfer
wafer-size mismatch and more efficient by substrate reuse [14]. Moreover, the developments in transfer
process, which is critical to reduce scattering loss when light is propagating along or through
printing
techniques have enabled a clean and atomically-smooth interface after the transfer process,
the interface.
which isIncritical
to reduce
loss when
light isvertical
propagating
along or through
the interface.
the section,
threescattering
types of lasers,
including
and edge-emitting
structures
based on
In
the
section,
three
types
of
lasers,
including
vertical
and
edge-emitting
structures
based on
NMs transfer printing, are reviewed from both fabrication and device performance perspectives.
NMs
transfer
printing,
are
reviewed
from
both
fabrication
and
device
performance
perspectives.
Furthermore, a GaN blue LED on a bendable substrate is also brought into discussion as a
Furthermore,
a of
GaN
blue LED
on a bendable
substrate is also brought into discussion as a
representative
the flexible
light-emitting
applications.
representative of the flexible light-emitting applications.
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2.1. Lasers
2.1. Lasers
2.1.1. Silicon-Based Vertical-Cavity Surface-Emitting Lasers
2.1.1. Silicon-Based Vertical-Cavity Surface-Emitting Lasers
The laser source has been one of the most challenging topics on the path to achieve an integrated
The
laser source
has been
of the
most challenging
topicshas
on to
thebepath
to achieve an integrated
silicon
photonics
platform.
Dueone
to the
indirect
bandgap, silicon
heterogeneously
silicon
photonics semiconductor
platform. Due to
the indirect
bandgap,
silicon has to
be heterogeneously
integrated
with compound
materials.
Promising
approaches,
including
direct growth
of III-V
with
compound
semiconductor
materials.
Promising
approaches,
including
direct
growth
of III-V
material on silicon substrate [45] and wafer boding between III-V and silicon [46,47],
are
material
on silicon
wafer
boding between
III-V and
silicon [46,47],
demonstrated
demonstrated
andsubstrate
reported.[45]
Theand
lattice
mismatches
and different
material
growth are
conditions
stand
and
reported.
Theforlattice
and as
different
material
conditions
stand
out aswire
big
out as
big issues
high mismatches
quality growth,
it is still
limitedgrowth
to quantum
dot or
quantum
issues
for high
quality growth,
as it isprovides
still limited
to quantum
applications.
Comparatively,
bonding
a more
practicaldot
wayortoquantum
bring thewire
III-Vapplications.
and silicon
Comparatively,
a more
practical way to
bring
the III-V
silicon together,
which
together, whichbonding
has beenprovides
employed
by edge-emitting
laser
designs
[47].and
However,
the wafer
size
has
been
employed
by
edge-emitting
laser
designs
[47].
However,
the
wafer
size
mismatch
and
III-V
mismatch and III-V substrate removal make inefficient use of material and consequently render this
substrate
approach removal
costly. make inefficient use of material and consequently render this approach costly.
Researcher Yang
Yangetetal.al.
reported
nanomembrane
transfer
printing-based
vertical-cavity
reported
nanomembrane
transfer
printing-based
vertical-cavity
surfacesurface-emitting
lasers
(VCSELs)
on
a
silicon
platform,
which
not
only
enjoys
similar
benefits
as
emitting lasers (VCSELs) on a silicon platform, which not only enjoys similar benefits as the bonding
the
bonding
process
in termscompatibility,
of mismatch but
compatibility,
also
makesuse
more
efficient
use of the
process
in terms
of mismatch
also makes but
more
efficient
of the
III-V material
by
III-V
material
by recycling
III-V2substrate.
2 shows
the schematic
SEM images
of the
recycling
the III-V
substrate.the
Figure
shows theFigure
schematic
and SEM
images of and
the vertical
laser cavity,
vertical
laser cavity,
which consists
of InGaAsP
quantum
wells as
gain
region
two Fanomembrane
resonance
which consists
of InGaAsP
quantum
wells as
gain region
and
two
Fanoand
resonance
membrane
reflectors
(MRs)
madecrystal
of single
crystal
silicon
device fabrication
processtwo-step
requires
reflectors (MRs)
made
of single
silicon
NMs.
The NMs.
deviceThe
fabrication
process requires
two-step
transfer-printing,
firstly
the
III-V
QW
NM
released
from
its
original
substrate
is
transferred
transfer-printing, firstly the III-V QW NM released from its original substrate is transferred on a
on
a patterned
as the
bottom
mirror,
then,
top
NMmirror
mirrorwith
withthe
theglass
glasssubstrate
substrate holder
patterned
SOI SOI
as the
bottom
mirror,
andand
then,
thethe
top
SiSi
NM
is stacked on top of quantum
quantum wells
wells (QWs).
(QWs). Between Si and QWs, there is hundreds
hundreds of
of nanometers
nanometers
thick SiO2 to achieve 6% field intensity confinement in the QWs region. Thus, a vertical cavity with a
III-V QW region sandwiched
sandwiched by
by two
two PC
PC mirrors
mirrors is
is formed.
formed.
Figure 2.
2. Vertical-cavity
Vertical-cavity surface-emitting
surface-emitting lasers
lasers (VCSEL)
(VCSEL) on
on silicon.
silicon. (a)
Schematic of
lasing cavity
cavity
Figure
(a) Schematic
of aa lasing
that
consists
of
five
layers
(t1–t5),
with
a
total
thickness
of
1–2
wavelengths.
An
InGaAsP
quantum
that consists of five layers (t1–t5), with a total thickness of 1–2 wavelengths. An InGaAsP quantum
well (QW)
(QW) is
is sandwiched
sandwiched between
between two
two single-layer
single-layer Si-MRs.
Si-MRs. Also
Also shown
shown is
is aa simulated
simulated electrical
electrical field
field
well
distribution
in
the
cavity
for
a
lasing
mode
at
1527
nm,
with
a
confinement
factor
of
6%.
(b)
A
cutout
distribution in the cavity for a lasing mode at 1527 nm, with a confinement factor of 6%. (b) A cutout
view of
of the
the complete
completeMR-VCSEL.
MR-VCSEL.(c)
(c)Illustration
Illustrationofofthe
themultilayer
multilayer
printing
process
formation
view
printing
process
forfor
thethe
formation
of
of
an
MR-VCSEL
(top
Si-MR/quantum
well/bottom
Si-MR).
The
diameter
of
the
active
area
is
D.
an MR-VCSEL (top Si-MR/quantum well/bottom Si-MR). The diameter of the active area is D. (d) SEM
(d) SEM
of InGaAsP
well disks/mesas
transferred
onto a bottom
Inset: optical
image
ofimage
InGaAsP
quantumquantum
well disks/mesas
transferred
onto a bottom
Si-MR. Si-MR.
Inset: optical
image,
2 bottom membrane reflector.
2
image,
showing
a
central
dark
region
representing
the
1
×
1
mm
showing a central dark region representing the 1 ˆ 1 mm bottom membrane reflector. (e) Zoom-in
(e) Zoom-in
view of one
InGaAsP
well
disk Si-MR.
on the Inset:
bottom
Si-MR. well
Inset:heterostructure,
quantum well
view
of one InGaAsP
quantum
well quantum
disk on the
bottom
quantum
heterostructure,
SEM image
of a complete
MR-VCSEL,
showing
anwell
InGaAsP
quantum well
disk
(f)
SEM image of a(f)complete
MR-VCSEL,
showing
an InGaAsP
quantum
disk sandwiched
between
sandwiched
between
top
and
bottom
Si-MRs.
Inset:
SEM
top
view
of
an
InGaAsP
quantum
well
top and bottom Si-MRs. Inset: SEM top view of an InGaAsP quantum well disk underneath a largedisk
top
underneath
large top from
Si-MR
layer (reprinted from [12]).
Si-MR
layer a(reprinted
[12]).
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By carefully adjusting the silicon photonic crystal Fano resonance peak spectrum, single mode
operation is achieved with a 532-nm optical pump source. The spectrum linewidth is 0.6 nm when
´2 for low temperature
operating
cm
operating above
above aa threshold
thresholdpump
pumppower
powerof
of88mW,
mW,which
whichisisabout
about0.32
0.32kW¨
kW·
cm−2 for
low temperature
(LT) (50
(50 K)
K) measurement.
measurement. As for room temperature (RT), the threshold is increased two times, and
the lasing linewidth nearly remains unchanged, as shown in Figure 3a. Furthermore, the wavelength
tunability is demonstrated by different PC lattice designs to shift the reflection spectrum towards the
target wavelength (Figure
(Figure 3b).
3b).
Figure 3.
3. (a)
(a) Laser
Laser Light-light
Light-light (L-L)
room temperature
temperature for
RT design
design of
of the
the MR-VCSEL
MR-VCSEL
Figure
(L-L) curve
curve at
at room
for the
the RT
device.
Inset:
measured
spectral
output
above
the
threshold
at
a
pump
power
of
36
mW,
(b)
device. Inset: measured spectral output above the threshold at a pump power of 36 mW, (b) Measured
Measured
MR-VCSEL spectral
and RT
RT designs:
designs: (i)
MR-VCSEL
spectral outputs
outputs at
at different
different temperatures
temperatures for
for both
both LT
LT and
(i) T
T == 10
10 K;
K;
(ii) T
T=
= 50
50 K;
K; (iii)
(iii) T
T=
= 120
120 K;
K; (iv)
(iv) T
T=
= 300
300 K.
K. Portions
Portions of
of measured
measured top
top (R
(Rt,, dash
dash lines)
lines) and
and bottom
bottom (R
(Rb,,
(ii)
t
b
solid lines)
lines) reflection
reflection spectra
spectra are
are also
also shown
shown for
for both
both LT
LT and
andRT
RTdesigns
designs(reprinted
(reprintedfrom
from[12]).
[12]).
solid
This provides a promising and practical approach to achieve full wafer-scale multi-wavelength
This provides a promising and practical approach to achieve full wafer-scale multi-wavelength
laser sources for silicon photonics. It is also worth noting that the whole cavity thickness is only
laser sources for silicon photonics. It is also worth noting that the whole cavity thickness is only
2.4 µ m and viable if transferred onto flexible plastic substrate, expanding its application in flexible
2.4 µm and viable if transferred onto flexible plastic substrate, expanding its application in flexible
optoelectronics and biophotonics.
optoelectronics and biophotonics.
2.1.2. Photonic Crystal Surface-Emitting Laser
2.1.2. Photonic Crystal Surface-Emitting Laser
The photonic crystal surface-emitting laser (PCSEL) has drawn much attention due to the
The photonic crystal surface-emitting laser (PCSEL) has drawn much attention due to the
advantages, including single mode, both longitudinally and transversely, low threshold, high power
advantages, including single mode, both longitudinally and transversely, low threshold, high power
and beam control [48–51]. The band edge effect is used to achieve zero group velocity, which
and beam control [48–51]. The band edge effect is used to achieve zero group velocity, which
theoretically has infinite gain at the specific wavelength; therefore, one lasing mode is selected
theoretically has infinite gain at the specific wavelength; therefore, one lasing mode is selected
dominantly over others. Then, the in-plane transmitting light waves are diffracted upwards out of
dominantly over others. Then, the in-plane transmitting light waves are diffracted upwards out
the cavity by the photonic crystal due to first order Bragg diffraction [48,49]. The critical requisite to
of the cavity by the photonic crystal due to first order Bragg diffraction [48,49]. The critical requisite to
form a PCSEL is that the light propagating in the cavity should, on the one hand, couple adequately
form a PCSEL is that the light propagating in the cavity should, on the one hand, couple adequately
with the PC cavity to fully make use of the band edge effect and, on the other hand, have a high
with the PC cavity to fully make use of the band edge effect and, on the other hand, have a high
confinement factor in the active region. Thus, it requires the appropriate distance proximity between
confinement factor in the active region. Thus, it requires the appropriate distance proximity between
the quantum well layer and the PC layer. For homogeneous material growth, this structure is realized
the quantum well layer and the PC layer. For homogeneous material growth, this structure is realized
by PC pattern definition etching and the QW regrowth process to ensure adequate feedback from
by PC pattern definition etching and the QW regrowth process to ensure adequate feedback from
different PC units by mode evanescent coupling with the PC cavity [49].
different PC units by mode evanescent coupling with the PC cavity [49].
Comparatively, NM transfer printing provides a simpler and lower-cost approach to bring the
Comparatively, NM transfer printing provides a simpler and lower-cost approach to bring the PC
PC structure and gain medium together. Deyin et al. demonstrated a novel approach to realize
structure and gain medium together. Deyin et al. demonstrated a novel approach to realize large-area
large-area PCSEL based on a heterogeneously-integrated III-V membrane transfer-printed onto a
PCSEL based on a heterogeneously-integrated III-V membrane transfer-printed onto a patterned
patterned silicon PC structure with SOI substrate. Figure 4a shows the schematic structure of the
silicon PC structure with SOI substrate. Figure 4a shows the schematic structure of the transferred
transferred InGaAsP multi-quantum well (MQW) layer on top of patterned Si PC layer. To compare
InGaAsP multi-quantum well (MQW) layer on top of patterned Si PC layer. To compare the effect
the effect of different coupling strengths on lasing performance, two devices with different spacing
of different coupling strengths on lasing performance, two devices with different spacing between
between MQWs and Si-PC (0 and 130 nm) are fabricated, named PCSEL-I and PCSEL-II. The SEM
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MQWs and Si-PC (0 and 130 nm) are fabricated, named PCSEL-I and PCSEL-II. The SEM image of the
transferred
membrane
on membrane
Si, the patterned
cavity
and cross-sectional
of the PCSEL-II
image of the
transferred
on Si,Sithe
patterned
Si cavity andview
cross-sectional
vieware
ofalso
the
shown
respectively
as in Figure
4b–d. as in Figure 4b–d.
PCSEL-II
are also shown
respectively
Figure 4.
4. Photonic
surface-emitting laser
(PCSEL) on
on silicon.
silicon. (a)
the hybrid
hybrid
Figure
Photonic crystal
crystal surface-emitting
laser (PCSEL)
(a) Schematic
Schematic of
of the
III-V/Si
PCSEL
cavity
on
Si
substrate,
which
consists
of
the
III-V
active
multi-quantum
well
(MQW)
III-V/Si PCSEL cavity on Si substrate, which consists of the III-V active multi-quantum well (MQW)
structure and
andthe
theSi-PC
Si-PCcavity.
cavity.Also
Alsoshown
shownis is
the
simulated
electrical
field
distribution
in the
cavity
structure
the
simulated
electrical
field
distribution
in the
cavity
for
for
a
lasing
mode
at
1424
nm.
(b)
An
SEM
image
of
the
InGaAsP
QW
disk/mesa
transferred
onto
a
a lasing mode at 1424 nm. (b) An SEM image of the InGaAsP QW disk/mesa transferred onto a Si-PC.
Si-PC.
(c)
Zoomed-in
view
of
the
defect-free
Si-PC
cavity.
(d)
Cross-sectional
view
of
the
cavity
(c) Zoomed-in view of the defect-free Si-PC cavity. (d) Cross-sectional view of the cavity (reprinted
(reprinted
from
[30]). from [30]).
Photoluminescences (PLs) are measured for the two types of designs, and temperaturePhotoluminescences (PLs) are measured for the two types of designs, and temperature-dependent
dependent characteristics are compared in terms of lasing power, linewidth, optical pump threshold,
characteristics are compared in terms of lasing power, linewidth, optical pump threshold, side mode
side mode suppression ratio (SMSR) and the output beam polarization property. The results as in
suppression ratio (SMSR) and the output beam polarization property. The results as in Figure 5 show
Figure 5 show that type I and II have different best-performance temperature at 25 K and 180 K,
that type I and II have different best-performance temperature at 25 K and 180 K, respectively.
Device I
respectively. Device I has a lower threshold pump power of 6 mW
(about 0.1 kW/cm2), compared to
2
has a lower threshold pump power of 6 mW (about 0.1 kW/cm ), compared to Device II with 25 mW
Device II with 25 mW (Figure 5a,d); while on the other hand, the PCSEL-II outperforms PCSEL-I,
(Figure 5a,d); while on the other hand, the PCSEL-II outperforms PCSEL-I, with respect to lasing
with respect to lasing spectrum linewidth and peak power, derived from Figure 5b,e.
spectrum linewidth and peak power, derived from Figure 5b,e.
The correlation between the lasing spectrum and simulated band diagram of the PC cavity is
The correlation between the lasing spectrum and simulated band diagram of the PC cavity is
found, which reveals the underlying physical explanations regarding the differences between the two
found, which reveals the underlying physical explanations regarding the differences between the two
designs. As more light is confined in Si for PCSEL-II, which has a thicker Si slab and a direct contact
designs. As more light is confined in Si for PCSEL-II, which has a thicker Si slab and a direct contact
between QWs and Si, the effective mode refractive index (n) for PCSEL-II is higher than PCSEL-I,
between QWs and Si, the effective mode refractive index (n) for PCSEL-II is higher than PCSEL-I,
since Si has higher n than the InP and InGaAsP material. As a result, the lasing modes’ wavelengths
since Si has higher n than the InP and InGaAsP material. As a result, the lasing modes’ wavelengths
for PCSEL-II (1505 nm) are red shifted compared to PCSEL-I (1425 nm). Thus, to obtain more gain,
for PCSEL-II (1505 nm) are red shifted compared to PCSEL-I (1425 nm). Thus, to obtain more gain,
higher temperature (180 K) is favored to red shift the QW PL spectrum to match the lasing mode
higher temperature (180 K) is favored to red shift the QW PL spectrum to match the lasing mode
wavelength. As for better performances in the narrow linewidth (0.6 nm) and lasing peak power of
wavelength. As for better performances in the narrow linewidth (0.6 nm) and lasing peak power
PCSEL-II, it is also attributed to stronger light confinement in PC Si, which induces a stronger
of PCSEL-II, it is also attributed to stronger light confinement in PC Si, which induces a stronger
feedback mechanism to achieve lasing. Both devices show one dominant polarization direction,
feedback mechanism to achieve lasing. Both devices show one dominant polarization direction, shown
shown as in Figure 5c,f. Comparing the two different structures and lasing characteristics, it is
as in Figure 5c,f. Comparing the two different structures and lasing characteristics, it is speculated
speculated that stronger coupling strength between QWs and the PC cavity could further improve
that stronger coupling strength between QWs and the PC cavity could further improve the lasing
the lasing properties, including peak power and linewidth.
properties, including peak power and linewidth.
Photonics 2016, 3, 40
6 of 19
Photonics 2016, 3, 40
6 of 18
Figure 5.
Figure
5. Lasing
Lasing characteristics.
characteristics. (a)
(a) Lasing
Lasing power
power and
and linewidth
linewidth versus
versus input
input pump
pump power
power for
for PCSEL-I
PCSEL-I
at
T
=
25
K.
(b)
Lasing
spectral
output
(plotted
in
semi-log
scale)
above
the
pumping
threshold
at T = 25 K. (b) Lasing spectral output (plotted in semi-log scale) above the pumping threshold (Inset:
(Inset:
far-field image).
image).(c)
(c)Measured
Measured
polarization
properties
above
threshold
λ = nm.
1424(d)
nm.
(d) Lasing
far-field
polarization
properties
above
threshold
at λ =at1424
Lasing
power
power
and linewidth
versuspump
inputpower
pumpfor
power
for PCSEL-II
at K.
T =(e)
180
K. (e)spectral
Lasing spectral
output
and
linewidth
versus input
PCSEL-II
at T = 180
Lasing
output (plotted
(plotted
in
semi-log
scale)
above
the
pumping
threshold
(Inset:
far-field
image).
(f)
Measured
in semi-log scale) above the pumping threshold (Inset: far-field image). (f) Measured polarization
polarization
properties
above
at λ = 1505 nm.
properties
above
threshold
at λthreshold
= 1505 nm.
With the membrane transfer printing technique, the heterogeneously-integrated band edge
With the membrane transfer printing technique, the heterogeneously-integrated band edge
surface-emitting laser provides a new promising approach to realize a large-scale single-mode laser
surface-emitting laser provides a new promising approach to realize a large-scale single-mode laser
source for silicon-based photonic platform.
source for silicon-based photonic platform.
2.1.3. Edge-Emitting Lasers
2.1.3. Edge-Emitting Lasers
Transfer printing is also applicable for III-V edge-emitting lasers based on silicon substrate [38].
Transfer printing is also applicable for III-V edge-emitting lasers based on silicon substrate [38].
John et al. demonstrated a wafer-scale integration of AlGaAs lasers on silicon using transfer printing
John et al. demonstrated a wafer-scale integration of AlGaAs lasers on silicon using transfer printing
of epitaxial layers, as shown in Figure 6. The two AlInGaAs QWs are grown on GaAs substrate with
of epitaxial layers, as shown in Figure 6. The two AlInGaAs QWs are grown on GaAs substrate with
a 1 µ m-thick Al0.95Ga0.05As sacrificial layer, which is etched away later to release the NM from the
a 1 µm-thick Al0.95 Ga0.05 As sacrificial layer, which is etched away later to release the NM from the
native substrate. To form the Fabry-Perot (FP) cavity after being transfer printed on silicon substrate,
native substrate. To form the Fabry-Perot (FP) cavity after being transfer printed on silicon substrate,
the mirror facets are etched using SiO2 by deep anisotropic inductively-coupled plasma (ICP), which
the mirror facets are etched using SiO2 by deep anisotropic inductively-coupled plasma (ICP), which
is independent of crystal orientation. The ridge waveguide is 3 µ m wide and 370 µ m long with single
is independent of crystal orientation. The ridge waveguide is 3 µm wide and 370 µm long with single
transverse mode. P- and n-type metal contacts are formed on top of the waveguide and the etched
transverse mode. P- and n-type metal contacts are formed on top of the waveguide and the etched
recess n-doping AlGaAs layer at one side of the waveguide, as shown in Figure 6b.
recess n-doping AlGaAs layer at one side of the waveguide, as shown in Figure 6b.
The electrical pumped edge-emitting lasers show comparable performances with the same sized
The electrical pumped edge-emitting lasers show comparable performances with the same sized
cleaved facet lasers on the original GaAs substrate under the continuous-wave current operation
cleaved facet lasers on the original GaAs substrate under the continuous-wave current operation
condition, shown as in Figure 7a. At room temperature, the threshold is 17 mA and 14 mA for silicon
condition, shown as in Figure 7a. At room temperature, the threshold is 17 mA and 14 mA for silicon
and GaAs substrate, respectively. The decrease in optical power collected from facet may result from
and GaAs substrate, respectively. The decrease in optical power collected from facet may result
the inefficient output light coupling, the p-type contact not fully covering the ridge near the facet
from the inefficient output light coupling, the p-type contact not fully covering the ridge near the
ends and increased n side lateral resistance with the thinner n-AlGaAs layer. Typical FP modes
facet ends and increased n side lateral resistance with the thinner n-AlGaAs layer. Typical FP modes
(Figure 7b) are observed with about a 0.2-nm spacing between adjacent longitudinal modes, which
(Figure 7b) are observed with about a 0.2-nm spacing between adjacent longitudinal modes, which
corresponds to the waveguide length of 370 µ m. The small signal measurement shows up to a 3-GHz
corresponds to the waveguide length of 370 µm. The small signal measurement shows up to a 3-GHz
direct modulation bandwidth (Figure 7c), with no obvious degradation compared to the one on the
direct modulation bandwidth (Figure 7c), with no obvious degradation compared to the one on the
native substrate. Furthermore, the light/current (L-I) characteristics are measured under different
native substrate. Furthermore, the light/current (L-I) characteristics are measured under different
temperatures for a 6 µ m-wide ridge (Figure 7d); at a 125-mA current injection, the edge emitting laser
temperatures for a 6 µm-wide ridge (Figure 7d); at a 125-mA current injection, the edge emitting laser
has a total power of 33 mW with a wall-plug efficiency of 13%.
has a total power of 33 mW with a wall-plug efficiency of 13%.
Photonics 2016, 3, 40
Photonics 2016, 3, 40
7 of 19
7 of 18
Photonics 2016, 3, 40
7 of 18
Figure 6.
of of
unprocessed
coupons
of epitaxial
material
fromfrom
a native
III-V
6. (a)
(a)Schematic
Schematicofofthe
thetransfer
transfer
unprocessed
coupons
of epitaxial
material
a native
wafer
(containing
the desired
layer
structure)
to the hosttocoupons
substrate.
laser devices
arefrom
fabricated
in
III-V
thethedesired
layer
structure)
the hostofThe
substrate.
The laser
devices
are
Figurewafer
6. (a)(containing
Schematic
of
transfer
of unprocessed
epitaxial
material
a native
parallel
on
the
host
substrate
using
lithographically-defined
etched
facets
to
align
to
the
underlying
fabricated
in
parallel
on
the
host
substrate
using
lithographically-defined
etched
facets
to
align
to
the
III-V wafer (containing the desired layer structure) to the host substrate. The laser devices are
alignment
(b) on
Schematic
a laser on
the
silicon
(reprinted
from
[38]). tofrom
underlying
marks.
(b)of
Schematic
of
a laser
onsubstrate
the silicon
substrate
(reprinted
fabricated marks.
inalignment
parallel
the host
substrate
using
lithographically-defined
etched
facets
align[38]).
to the
underlying alignment marks. (b) Schematic of a laser on the silicon substrate (reprinted from [38]).
Figure 7. (a) Optical power as a function of current from a 3 µ m-wide ridge, 370 µ m-long laser
fabricated
on silicon,
similar device
fabricated
a standard
cleaved
on native
Figure 7. (a)
Opticalcompared
power as to
a afunction
of current
from ausing
3 µ m-wide
ridge,
370 facet
µ m-long
laser
Figure 7. (a) Optical power as a function of current from a 3 µm-wide ridge, 370 µm-long laser
GaAs
substrate.
(b) Spectrum
ofto
the
laser showing
the
multiple
longitudinal
mode
emission.
(c)native
Small
fabricated
on
silicon,
compared
a
similar
device
fabricated
using
a
standard
cleaved
facet
on
fabricated on silicon, compared to a similar device fabricated using a standard cleaved facet on native
signal
modulation
silicon the
as amultiple
functionlongitudinal
of operatingmode
current
from 30–60
mA.
GaAs substrate.
substrate.
(b)response
Spectrumofof
ofthe
thelaser
laseron
showing
emission.
(c) Small
Small
GaAs
(b)
Spectrum
the
laser
showing
the multiple
longitudinal mode
emission.
(c)
(d)
Temperature
dependence
of
the
output
power
as
a
function
of
current
from
a
6
µ
m-wide
ridge,
signal
modulation
response
of
the
laser
on
silicon
as
a
function
of
operating
current
from
30–60
signal modulation response of the laser on silicon as a function of operating current from 30–60 mA.
mA.
370
µ
m-long
laser
fabricated
on
silicon
(reprinted
from
[38]).
(d)
Temperature
dependence
of
the
output
power
as
a
function
of
current
from
a
6
µ
m-wide
ridge,
(d) Temperature dependence of the output power as a function of current from a 6 µm-wide ridge,
370 µm-long
µ m-long laser
laser fabricated
fabricated on
on silicon
silicon (reprinted
(reprinted from
from [38]).
[38]).
370
In this work, the transfer printing method has been successfully proven to be applicable in
In this work,
the transfer
printing
method onto
has been
successfully
proven
to bephotonics
applicableand
in
the wafer-scale
integration
of III-V
active material
non-native
substrates
in silicon
In this work, the transfer printing method has been successfully proven to be applicable in the
the wafer-scale
integration of III-V active material onto non-native substrates in silicon photonics and
flexible
optoelectronics.
wafer-scale integration of III-V active material onto non-native substrates in silicon photonics and
flexible optoelectronics.
flexible
optoelectronics.
2.2. Flexible
Light-Emitting Diode
2.2. Flexible Light-Emitting Diode
Recently, we have reported transfer printing-based flexible blue LEDs by transferring the GaN
Recently,
have reported
transfer printing-based
flexible
blue
LEDs
by transferring
the GaN
membrane
on we
a flexible
plastic substrate
by transfer printing
[44].
Due
to the
lattice mismatch,
the
membrane on a flexible plastic substrate by transfer printing [44]. Due to the lattice mismatch, the
Photonics 2016, 3, 40
8 of 19
2.2. Flexible Light-Emitting Diode
Recently, we have reported transfer printing-based flexible blue LEDs by transferring the GaN
membrane
a 3,flexible
plastic substrate by transfer printing [44]. Due to the lattice mismatch,
Photonicson
2016,
40
8 of 18 the
GaN buffer layer before QW growth on sapphire substrates needs to be at least a few microns thick in
buffer layer
before QWGaN
growth
on sapphire
needs
to be at
leastwould
a few microns
orderGaN
to achieve
an acceptable
crystal
quality.substrates
As a result,
built-in
stress
inducethick
fractures
in
order
to
achieve
an
acceptable
GaN
crystal
quality.
As
a
result,
built-in
stress
would
induceif not
when laser lift-off (LLO) is applied to separate the GaN structure from the sapphire substrate
fractures when laser lift-off (LLO) is applied to separate the GaN structure from the sapphire
tightly bonded to a mechanically-compatible substrate. It is proposed in this report that elastic and
substrate if not tightly bonded to a mechanically-compatible substrate. It is proposed in this report
soft PDMS is employed to strongly bond the GaN layer during the LLO process, and then, the stress
that elastic and soft PDMS is employed to strongly bond the GaN layer during the LLO process, and
is fully
relaxed
after is
being
onto
a polyethylene
terephthalate
(PET)
stretchable (PET)
substrate.
then,
the stress
fullytransferred
relaxed after
being
transferred onto
a polyethylene
terephthalate
Figure
8 shows substrate.
the main Figure
process
flows the
andmain
LEDprocess
chip image
stretchable
8 shows
flows on
andPET.
LED chip image on PET.
Figure 8. Schematic of the fabrication process for GaN LEDs on a PET substrate using a laser lift-off
Figure 8. Schematic of the fabrication process for GaN LEDs on a PET substrate using a laser lift-off
(LLO) and transfer-printing method. (a) Fabrication of GaN LEDs on a sapphire substrate. (b) Place
(LLO)fabricated
and transfer-printing
Fabrication
of GaN
LEDs lift-off
on a sapphire
(b) Place
GaN LEDs onmethod.
a PDMS(a)
elastomeric
stamp.
(c) Laser
from thesubstrate.
sapphire side.
fabricated
GaN
LEDs
on
a
PDMS
elastomeric
stamp.
(c)
Laser
lift-off
from
the
sapphire
side.
(d)
Gentle
(d) Gentle removal of the sapphire substrate. (e) Transfer-print GaN LED layer onto the PET substrate.
removal
of
the
sapphire
substrate.
(e)
Transfer-print
GaN
LED
layer
onto
the
PET
substrate.
(f)
Curing
(f) Curing of the adhesive layer to permanently bond the transfer-printed GaN LED layer. An optical
of thefiber
adhesive
layer
to permanently
bond
the collection.
transfer-printed
GaN
LED
layer. LED
An optical
is
is placed
on top
of the GaN layer
for light
(g) Image
of the
fabricated
array onfiber
a
substrate.
(h)layer
Zoomed-in
image
of an individual
LED
on PET
(reprinted
from
[44]).
placedbent
on PET
top of
the GaN
for light
collection.
(g) Image
of the
fabricated
LED
array
on a bent PET
substrate. (h) Zoomed-in image of an individual LED on PET (reprinted from [44]).
Both electrical and optical performances are measured and compared between LED chips on
sapphire substrate and PET after the transfer-printing process. From the I-V and P-I shown in
Both electrical and optical performances are measured and compared between LED chips on
Figure 9a, the LEDs on PET substrates have a slightly smaller current and reduced optical output
sapphire
substrate
and
PETcurrent.
after the
transfer-printing
process.
From
the I-V and
P-I
shownby
inPET’s
Figure 9a,
power
under the
same
This
may be attributed
to the heat
dissipation
issue
induced
the LEDs
onthermal
PET substrates
havethan
a slightly
smaller
reduced
opticalsigns
output
power
under
poorer
conductivity
sapphire,
whichcurrent
did notand
show
any melting
during
tests,
the same
current.
Thisspectra
may be
attributed
to current
the heatfordissipation
issue
induced
by PET’s
however.
Optical
under
a 10-mA
the two cases
in Figure
9b show
that poorer
the peakthermal
is
conductivity
than
did
nottransfer
show any
melting
during The
tests,
however.shift
Optical
shifted from
457sapphire,
nm to 455which
nm after
being
printed
on the signs
PET substrate.
wavelength
is speculated
to originate
from
stress
band
spectra
under a 10-mA
current
forthe
therelaxed
two cases
in and
Figure
9bfilling
showeffects.
that the peak is shifted from 457 nm
Photonics 2016, 3, 40
Photonics 2016, 3, 40
9 of 19
9 of 18
to 455 nm after being transfer printed on the PET substrate. The wavelength shift is speculated to
This method of using PDMS as the LLO and transfer holder provides a simplified approach to
originate from the relaxed stress and band filling effects.
fabricate GaN LEDs on any flexible substrate without performance degradation.
Figure 9. (a) Light output power-current-voltage (L-I-V) characteristics and (b) electroluminescent
Figure 9. (a)
output
power-current-voltage
(L-I-V)
characteristics
electroluminescent
lightLight
spectra
of the GaN
LEDs on sapphire substrate
(before
laser lift-off) andand
PET (b)
substrates
(after
transfer-printing).
The insert
in Figure 9b
shows the(before
light emission
images on
a PET
light spectra
of the GaN LEDs
on sapphire
substrate
laser lift-off)
and
PETsubstrate
substrates (after
(reprintedThe
frominsert
[44]). in Figure 9b shows the light emission images on a PET substrate (reprinted
transfer-printing).
from [44]).
3. Semiconductor Nanomembrane-Based Photodetecting Devices
To achieve a monolithically-integrated photonics circuit on a silicon platform, integrating an
This method
of using
PDMS
theSiLLO
andhighly
transfer
holder
provides
a simplified
approach to
efficient light
absorption
layeras
onto
has been
desirable.
Approaches
developed
up to now
include
mainly
boding orsubstrate
epitaxial growth
[52].performance
Lattice mismatches
between Si and Ge or Si
fabricate GaN
LEDs
onwafer
any flexible
without
degradation.
and III-V will greatly degrade the material quality with large dislocations and defect density.
Benefiting from
being insensitive to lattice
mismatch, transfer
printing enjoys advantages over the
3. Semiconductor
Nanomembrane-Based
Photodetecting
Devices
two methods in terms of low cost and process simplification.
In athis
section, photodetecting devices
based on InGaAs
NMs on
Si substrate
are
To achieve
monolithically-integrated
photonics
circuit and
on aGesilicon
platform,
integrating
an
reviewed,
including
a multi-wavelength
photodetector
a cavity-enhanced
photodetector.
On theup to now
efficient light
absorption
layer
onto Si has been
highlyand
desirable.
Approaches
developed
other hand, flexible phototransistors and photodetectors based on InP and Si NMs on plastic
include mainly wafer boding or epitaxial growth [52]. Lattice mismatches between Si and Ge or Si and
substrate transfer have also been demonstrated, offering a promising route to an inorganic
III-V will greatly
degrade
the material
quality with large dislocations and defect density. Benefiting
crystalline-based
flexible
photonics platform.
from being insensitive to lattice mismatch, transfer printing enjoys advantages over the two methods
Multi-Color Photodetector Arrays
in terms of3.1.
low
cost and process simplification.
A multi-color
photodetector
covering
visible
and infrared
(IR)NMs
has long
desired are
for reviewed,
In this section,
photodetecting
devices
based
on InGaAs
and Ge
on Sibeen
substrate
applications, such as biophotonics, automotive cameras, imaging, free space optical communications,
including a multi-wavelength photodetector and a cavity-enhanced photodetector. On the other hand,
and so on. The conventional approach to discriminate and detect different wavelengths is by the use
flexible phototransistors
and photodetectors
based on InP
and Si NMs
of filters, which is slow,
bulky and requires complicated
post-processing
[53].on
As plastic
differentsubstrate
materials transfer
have also been
demonstrated,
offering
a
promising
route
to
an
inorganic
crystalline-based
have different optical absorption spectra, membrane transfer offers a feasible way to form stacked flexible
heterogeneous material layers, thus enabling absorption and sensing targeting at different
photonics platform.
wavelengths at the same time.
filter-free four-color
photodetector based on integrated InGaAs and Si membrane over the
3.1. Multi-ColorA Photodetector
Arrays
visible and IR spectrum has been recently demonstrated [39], shown as in Figure 10. Figure 10a is the
epi-layer structures
of SOI wafercovering
and InGaAsvisible
on InP substrate
before the(IR)
transfer
silicon
A multi-color
photodetector
and infrared
hasprocess.
long The
been
desired for
detecting part is a vertical n-p-n-p, forming three junctions capable of detecting blue, green and red
applications, such as biophotonics, automotive cameras, imaging, free space optical communications,
colors due to the wavelength-dependent absorption property of silicon [54], while the InGaAs section
and so on.has
The
conventional
approach
discriminate
detect
different
wavelengths
a p-i-n
single junction
structure,to
which
responds to and
the NIR
wavelengths.
Before
the transfer, is
theby the use
of filters, which
slow, bulky
and
requires
post-processing
As different
InGaAsis
substrate
is etched
to define
mesa complicated
and contact areas
and spun with SU-8[53].
to facilitate
bonding materials
between
the Si membrane
andspectra,
InGaAs substrate.
Then, transfer
the released
Si membrane
from SOI
transfer
have different
optical
absorption
membrane
offers
a feasible
wayis to
form stacked
printed onto the InP substrate with careful alignment to ensure that the two detecting parts are closely
heterogeneous
material layers, thus enabling absorption and sensing targeting at different wavelengths
placed (Figure 10b). The thickness of Si is 6.5 µ m, and the InGaAs photodetecting part is 2.56 µ m. In
at the same time.
A filter-free four-color photodetector based on integrated InGaAs and Si membrane over the
visible and IR spectrum has been recently demonstrated [39], shown as in Figure 10. Figure 10a is the
epi-layer structures of SOI wafer and InGaAs on InP substrate before the transfer process. The silicon
detecting part is a vertical n-p-n-p, forming three junctions capable of detecting blue, green and red
colors due to the wavelength-dependent absorption property of silicon [54], while the InGaAs section
has a p-i-n single junction structure, which responds to the NIR wavelengths. Before the transfer, the
InGaAs substrate is etched to define mesa and contact areas and spun with SU-8 to facilitate bonding
between the Si membrane and InGaAs substrate. Then, the released Si membrane from SOI is transfer
Photonics 2016, 3, 40
10 of 19
printed
onto the InP substrate with careful alignment to ensure that the two detecting parts 10
areof closely
Photonics 2016, 3, 40
18
placed (Figure 10b). The thickness of Si is 6.5 µm, and the InGaAs photodetecting part is 2.56 µm. In
the end,
four four
contacts
areare
formed
forforthree
betweenn-p-n-p
n-p-n-pSi,Si,
and
contacts
are defined
the end,
contacts
formed
threejunctions
junctions between
and
twotwo
contacts
are defined
p and
n layers
of InGaAs,
Figure10c.
10c.
on theonpthe
and
n layers
of InGaAs,
asas
ininFigure
Photonics 2016, 3, 40
10 of 18
the end, four contacts are formed for three junctions between n-p-n-p Si, and two contacts are defined
on the p and n layers of InGaAs, as in Figure 10c.
Figure
10. Schematics
of the proposed
crystalline-nanomembrane-based
multicolor
Figure
10. Schematics
of the proposed
crystalline-nanomembrane-based
stackedstacked
multicolor
multiband
multiband
photodetector
arrays.
(a)
Three-junction
SOI
wafer
and
the
InGaAs
single-junction
wafer
photodetector arrays. (a) Three-junction SOI wafer and the InGaAs single-junction wafer before
transfer.
Figure
10.
Schematics
of
the
proposed
crystalline-nanomembrane-based
stacked
multicolor
before
transfer.
(b)
Si
pixels
transferred
onto
the
InP
substrate
with
precise
alignment
with
the
InGaAs
(b) Si pixels transferred onto the InP substrate with precise alignment with the InGaAs pixel. (c) One
multiband
(a) Three-junction SOImembrane
wafer and the
InGaAsafter
single-junction
wafer
One photodetector
pixel
of thearrays.
multicolor
imager
device completion
pixel pixel.
of the (c)
multicolor
multiband
membranemultiband
imager after device completion
(reprinted
from [39]).
beforefrom
transfer.
(b) Si pixels transferred onto the InP substrate with precise alignment with the InGaAs
(reprinted
[39]).
pixel. (c) One pixel of the multicolor multiband membrane imager after device completion
(reprinted from
[39]).
The The
photocurrent
responses
lightwavelengths
wavelengths
intensities
photocurrent
responsesunder
underdifferent
different incident
incident light
andand
intensities
are are
measured
for the
The The
dark
currents
forincident
all
are below
20 nA
with
a ´2-V
reverse
measured
forfour
the junctions.
four junctions.
dark
currents
forjunctions
all light
junctions
are below
20
nA with
The
photocurrent
responses
under
different
wavelengths
and
intensities
area −2-V
bias.
With
light
thedark
center
of
individual
device
through
a the
lensed
fiber, the for
bias. reverse
With measured
light
shined
on
theshined
centeron
ofThe
individual
device
aare
lensed
fiber,
responsivities
for the
four
junctions.
currents
for allthrough
junctions
below
20 nA
with
a −2-V
for IR
blue,
green,
red and
IR
wavelengths
(4.5
532980
nm,
632and
nm,
980
nm
andare
1550
nm)A/W,
reverse
bias.
With
light shined
on
thenm,
center
individual
device
through
a 1550
lensed
fiber,
the0.09
blue, responsivities
green,
red and
wavelengths
(4.5
532ofnm,
632nm,
nm,
nm
nm)
responsivities
for blue,
green,
red
and
IR wavelengths
(4.5respectively,
nm, 532 nm, 632
nm,
980 nm
and 1550
nm)
are
0.09
A/W,
0.1
A/W,
0.15
A/W,
0.5
A/W
and
0.8
A/W,
as
shown
in
Figure
11.
0.1 A/W, 0.15 A/W, 0.5 A/W and 0.8 A/W, respectively, as shown in Figure 11.
are 0.09 A/W, 0.1 A/W, 0.15 A/W, 0.5 A/W and 0.8 A/W, respectively, as shown in Figure 11.
Figure 11. Simulated (solid lines) and measured (symbols) responsivity for (a) silicon (405 nm, 532 nm,
Figure
11.632
Simulated
(solid
lines)
andmeasured
measured
(symbols)
responsivity
(a) (a)
silicon
(405(405
nm, nm,
532 nm,
Figure
11. and
Simulated
(solid
lines)
and
(symbols)
responsivity
silicon
532 nm,
nm) and
(b)
InGaAs
(IR–980
nm, 1550 nm)
(reprinted
from [39]). forfor
and
632
nm)
and
(b)
InGaAs
(IR–980
nm,
1550
nm)
(reprinted
from
[39]).
and 632 nm) and (b) InGaAs (IR–980 nm, 1550 nm) (reprinted from [39]).
This work demonstrates the capability of integrating a variety of materials with different optical
properties
to make one the
photodetector
more versatile
and of
multi-functional,
This
work demonstrates
capability unit
of integrating
a variety
materials with enabled
differentbyoptical
This
work
demonstrates
capability of
integrating
a variety
materials with different
optical
membrane
transfer-printing.
properties
to make
one the
photodetector
unit
more versatile
andofmulti-functional,
enabled by
properties
to make
one photodetector unit more versatile and multi-functional, enabled by membrane
membrane
transfer-printing.
3.2. Germanium Photodetector with Enhanced Quantum Efficiency
transfer-printing.
Recently,
we reported
resonant
cavity
(RC) metal-semiconductor-metal
(MSM) germanium
3.2. Germanium
Photodetector
with
Enhanced
Quantum
Efficiency
nanomembrane
(Ge NM)
photodetectors
via stacked single-crystalline
NMs by transfer printing. The
3.2. Germanium
Photodetector
with
Enhanced Quantum
Efficiency
Recently,
we released
reported
resonant
cavity
(RC)germanium-on-insulator
metal-semiconductor-metal
(MSM)
germanium
Ge NM layer,
from
smart-cut
processed
wafer [55],
was directly
nanomembrane
(Ge
NM)
photodetectors
via
stacked
single-crystalline
NMs
by
transfer
printing.
The
transferred
onto the Si NM/SiO
2 distributed
(DBR). Therefore, a high quality
Ge NM,
Recently,
we reported
resonant
cavity Bragg
(RC) reflector
metal-semiconductor-metal
(MSM)
germanium
free
from
misfit/threading
dislocations,
was
obtained.
The
two
pairs
of
Si
NM/SiO
2 DBR were
realized
Ge
NM
layer,
released
from
smart-cut
processed
germanium-on-insulator
wafer
[55],
was
directly
nanomembrane (Ge NM) photodetectors via stacked single-crystalline NMs by transfer printing.
by repeating
the Si
single
crystal
Si NM transfer
and partially
wet
oxidization
process
twice,
as shown
transferred
onto
the
NM/SiO
2 distributed
Bragg
reflector
(DBR).
Therefore,
a high
quality
The Ge
NM layer,
released
from smart-cut
processed
germanium-on-insulator
wafer
[55], Ge
wasNM,
directly
in Figure
12a–e. The thicknesses
of SiO
2 and Si NM after oxidation were 270 and 110 nm, which are
free from
misfit/threading
dislocations,
was
obtained. The two pairs of Si NM/SiO2 DBR were realized
transferreddesigned
onto the
NM/SiO
Bragg areflector
Therefore,
a high
quality Ge NM,
2 distributed
to Si
have
high and
reflectivity
1.55-µ m (DBR).
wavelength
range. After
the second
by repeating the
single
crystal Siflat
NM
transfer over
and partially
wet
oxidization
process twice,
as shown
oxidation, 570 nm-thick
Ge NM was was
transferred
onto the
two-pair
DBR (Figure
12f). In the2 end,
free from misfit/threading
dislocations,
obtained.
The
two pairs
of Si NM/SiO
DBRTi/Au
were realized
in Figure 12a–e. The thicknesses of SiO2 and Si NM after oxidation were 270 and 110 nm, which are
by repeating
the
single
crystal
Si
NM
transfer
and
partially
wet
oxidization
process
twice,
as shown
designed to have high and flat reflectivity over a 1.55-µ m wavelength range. After the second
in Figure
12a–e.
thicknesses
of SiO
NMtheafter
oxidation
were 12f).
270 In
and
which
2 and Sionto
oxidation,
570The
nm-thick
Ge NM was
transferred
two-pair
DBR (Figure
the110
end,nm,
Ti/Au
are designed to have high and flat reflectivity over a 1.55-µm wavelength range. After the second
Photonics 2016, 3, 40
11 of 19
oxidation, 570 nm-thick Ge NM was transferred onto the two-pair DBR (Figure 12f). In the end, Ti/Au
Photonics 2016, 3, 40
11 of 18
(10 nm/500 nm) was deposited as the anode and cathode contact metals, as shown in Figure 12g.
Figure 12h(10shows
microscope
image
the completed
device.
The
and spacing
nm/500the
nm)optical
was deposited
as the anode
andof
cathode
contact metals,
as shown
in width
Figure 12g.
Figure electrodes
12h shows the
optical
microscope
image of the completed
device. The
width and
spacing structure
between metal
are
5 and
2 µm, respectively.
As a reference
sample,
a similar
between metal electrodes are 5 and 2 µ m, respectively. As a reference sample, a similar structure
without DBR
is fabricated, as well.
Photonics 2016, 3, 40
11 of 18
without DBR is fabricated, as well.
(10 nm/500 nm) was deposited as the anode and cathode contact metals, as shown in Figure 12g.
Figure 12h shows the optical microscope image of the completed device. The width and spacing
between metal electrodes are 5 and 2 µ m, respectively. As a reference sample, a similar structure
without DBR is fabricated, as well.
Figure 12. Schematic illustrations of the fabrication process for the resonant cavity (RC)
Figure 12.metal-semiconductor-metal
Schematic illustrations
fabrication
processSi for
cavity (RC)
(MSM) of
Ge the
photodetectors.
(a) Transfer
NM the
with resonant
PDMS stamp.
metal-semiconductor-metal
(MSM)
Ge
photodetectors.
(a) Transfer
with
PDMS
stamp.
(b) Transferred Si NM on
a quartz
substrate.
(c) Thermal oxidation
after firstSiSi NM
NM. (d)
Second
Si
NM transfer
afteron
oneapair
of Si/SiO
2 distributed
Bragg
reflectoroxidation
(DBR). (e) Second
(b) Transferred
Si NM
quartz
substrate.
(c)
Thermal
after thermal
first Sioxidation.
NM. (d) Second
(f) Transferred Ge NM on two pairs of Si/SiO2 DBR. (g) Complete device after Ti/Au electrode
Si NM transfer after one pair of Si/SiO2 distributed Bragg reflector (DBR). (e) Second thermal oxidation.
Figure
12. and
Schematic
illustrations
of the image
fabrication
the resonant The
cavity
deposition
lift-off. (h)
Optical microscope
of the process
RC MSMfor
Ge photodetector.
scale(RC)
bar
(f) Transferred
Ge
NM onfrom
two
pairs
Complete
device
2 DBR. (g)
metal-semiconductor-metal
(MSM)ofGeSi/SiO
photodetectors.
(a) Transfer
Si NM
with after
PDMSTi/Au
stamp. electrode
is 50 µ m
(reprinted
[40]).
deposition(b)
and
lift-off. (h)
Optical
microscope
image
of theoxidation
RC MSM
Gefirst
photodetector.
TheSiscale bar is
Transferred
Si NM
on a quartz
substrate.
(c) Thermal
after
Si NM. (d) Second
NM
transfer
after
one
pair
of
Si/SiO
2
distributed
Bragg
reflector
(DBR).
(e)
Second
thermal
oxidation.
To
compare
the
photo
responsivity
of
the
two
type
of
devices,
a
tunable
laser
source
is
connected
50 µm (reprinted from [40]).
(f) Transferred
NM the
on two
2 DBR. (g) Complete
device after Ti/Au
electrode The
to a lensed
fiber to Ge
couple
lightpairs
into of
theSi/SiO
photodetectors
for the photocurrent
measurement.
and lift-off.
microscope image
the RC MSM
Ge photodetector.
The scale
darkdeposition
and photocurrent
of (h)
theOptical
Ge photodetectors
wereof
measured,
as shown
in Figure 13a,b.
As bar
a result,
is 50the
µ m (reprinted
from
[40]).
To compare
photo
of the
two type
ofµdevices,
laser
source is connected
responsivities
of 0.18responsivity
and
0.09
A/W were
measured
at 1.55
m under 1aVtunable
for the MSM
photodetector
DBRto
and
the onethe
on light
quartz,into
respectively.
The quantum efficiency
of the RC Ge photodetector
with The dark
to a lensedon
fiber
couple
the photodetectors
for the photocurrent
measurement.
compare
the photo
responsivity
of the
two
of devices,
a tunable
laser source is connected
DBRTo
(17.3%)
is about
two-times
larger than
the
onetype
on quartz
substrate
(8.3%).
and photocurrent
thetoGe
photodetectors
measured,
as photocurrent
shown in Figure
13a,b.The
As a result,
to a lensedof
fiber
couple
the light into thewere
photodetectors
for the
measurement.
responsivities
of 0.18
and 0.09
were measured
1.55 µmasunder
1 Figure
V for 13a,b.
the MSM
photodetector
dark and
photocurrent
of A/W
the Ge photodetectors
wereat
measured,
shown in
As a result,
responsivities
of quartz,
0.18 and 0.09
A/W were measured
at 1.55 µ efficiency
m under 1 Vof
forthe
the MSM
photodetector
on DBR and
the one on
respectively.
The quantum
RC Ge
photodetector with
on DBR and the one on quartz, respectively. The quantum efficiency of the RC Ge photodetector with
DBR (17.3%) is about two-times larger than the one on quartz substrate (8.3%).
DBR (17.3%) is about two-times larger than the one on quartz substrate (8.3%).
Figure 13. Measured photo/dark current of (a) the RC MSM Ge photodetector and (b) the MSM Ge
photodetector on quartz substrate (reprinted from [40]).
3.3. Large-Area InP NM-Based Flexible Photodetectors
The flexible optoelectronic device has a variety of applications, such as flexible imaging,
Figure 13. Measured photo/dark current of (a) the RC MSM Ge photodetector and (b) the MSM Ge
photonic
systems and
bio-photonics.
Due
toMSM
the rigidity
and fragility ofand
bulk(b)
crystalline
Figureconformal
13.photodetector
Measured
photo/dark
current
of (a)from
the
RC
Ge photodetector
the MSM Ge
on quartz substrate
(reprinted
[40]).
semiconductor materials, conventional flexible devices are mostly based on organic or amorphous
photodetector on quartz substrate (reprinted from [40]).
material.
The transfer
printingFlexible
technique
allows one to combine the advantages of high performance
3.3.
Large-Area
InP NM-Based
Photodetectors
inorganic crystalline material and mechanical flexibility of thin NM at the nanometer scale. While for
optoelectronic
device has a variety of applications, such as flexible imaging,
3.3. Large-AreaThe
InPflexible
NM-Based
Flexible Photodetectors
conformal photonic systems and bio-photonics. Due to the rigidity and fragility of bulk crystalline
The flexible
optoelectronic
device has
a variety
ofmostly
applications,
suchorasamorphous
flexible imaging,
semiconductor
materials, conventional
flexible
devices are
based on organic
material.
The
transfer
printing
technique
allows
one
to
combine
the
advantages
of
high
performance
conformal photonic systems and bio-photonics. Due to the rigidity and fragility of bulk crystalline
inorganic crystalline material and mechanical flexibility of thin NM at the nanometer scale. While for
semiconductor materials, conventional flexible devices are mostly based on organic or amorphous
material. The transfer printing technique allows one to combine the advantages of high performance
inorganic crystalline material and mechanical flexibility of thin NM at the nanometer scale. While
Photonics 2016, 3, 40
12 of 19
Photonics 2016, 3, 40
12 of 18
for particularly fragile InP material, large-area release and transfer still is challenging, we came up
with aparticularly
frame-assisted
transfer
(FAMT)
process
to dealstill
with
the large-area
fragilemembrane
InP material,
large-area
release
and transfer
is challenging,
we and
cameeasy-to-break
up with
Photonics 2016, 3, 40
12 of 18
2
membrane
material.membrane
In this report,
a 3(FAMT)
ˆ 3 mm
InP to
NM
is with
released
from the and
native
substrate
and
a frame-assisted
transfer
process
deal
the large-area
easy-to-break
2 InP NM
transferred
to PET
substrate.
InP structure
consists
of is
a p-i-n
photodetecting
diode
and aand
InGaAs
membrane
material.
In thisThe
report,
a 3 × 3 mm
released
from the native
substrate
particularly fragile InP material, large-area release and transfer still is challenging, we came up with
transferred
to PET substrate.
The
InP structure
consists of a p-i-n
photodetecting
andBefore
a InGaAs
sacrificial
layer underneath
[56],transfer
which
will
be etched
during
etchingdiode
release.
the etch
a frame-assisted
membrane
(FAMT)
processaway
to deal
with wet
the large-area
and easy-to-break
sacrificial
layer
underneath
[56],
which
will
be
etched
away
during
wet
etching
release.
Before
the
and release
process,
two In
frame
finger-shaped
metals
top the
of InP
NMs,
actingand
both as
2 InPare
membrane
material.
this report,
a 3 × 3 mm
NMdeposited
is releasedon
from
native
substrate
etch and
release
process,
frame finger-shaped
metals
are deposited
on top
ofNM.
InP NMs,
acting
the anode
metal
andtwo
mechanical
support
for
the
large-area
InPdiode
AsaFigure
transferred
tocontact
PET substrate.
The InP structure
consists
of afragile
p-i-n photodetecting
and
InGaAs14a,b
both as the anode metal contact and mechanical support for the fragile large-area InP NM. As
sacrificial
[56],on
which
will be
during substrate,
wet etchingand
release.
the as a
depicts,
the InPlayer
NMunderneath
is transferred
indium
tinetched
oxide away
(ITO)/PET
ITO Before
functions
Figure 14a,b depicts, the InP NM is transferred on indium tin oxide (ITO)/PET substrate, and ITO
etch and
release metal.
process, two frame finger-shaped metals are deposited on top of InP NMs, acting
transparent
cathode
functions as a transparent cathode metal.
both as the anode metal contact and mechanical support for the fragile large-area InP NM. As
Figure 14a,b depicts, the InP NM is transferred on indium tin oxide (ITO)/PET substrate, and ITO
functions as a transparent cathode metal.
Figure 14. (a) Cross-sectional and (b) three-dimensional views of flexible InP p-i-n NM photodetecting
Figure 14. (a) Cross-sectional and (b) three-dimensional views of flexible InP p-i-n NM photodetecting
(PD) on ITO/PET substrate. (c) A micrograph of fabricated flexible InP PD under test. (d–f) Zoom-in
(PD) views
on ITO/PET
substrate.
A (3
micrograph
ofPD
fabricated
flexible
InP PD(reprinted
under test.
(d–f)
Zoom-in
of a fabricated
large(c)
area
× 3 mm2) InP
on flexible
PET substrate
from
[41]).
Figure
14.
(a)
Cross-sectional
and
(b)
three-dimensional
views
of
flexible
InP
p-i-n
NM
photodetecting
2
views of a fabricated large area (3 ˆ 3 mm ) InP PD on flexible PET substrate (reprinted from [41]).
(PD) on ITO/PET substrate. (c) A micrograph of fabricated flexible InP PD under test. (d–f) Zoom-in
The photodetecting performances are2 measured, as shown in Figure 15; the dark current is as
views of a fabricated large area (3 × 3 mm ) InP PD on flexible PET substrate (reprinted from [41]).
low as
1 µ A at a reverse
bias of −0.5 V.
at a 533-nm
wavelength
is incident
devices
with is as
The
photodetecting
performances
areLight
measured,
as shown
in Figure
15; theondark
current
different power; the photocurrent shows a nearly linear trend versus the light intensity (Figure 15b).
Theat
photodetecting
performances
measured,
as shown
in Figure is
15;incident
the dark on
current
is aswith
low as 1 µA
a reverse bias
of ´0.5 V. are
Light
at a 533-nm
wavelength
devices
The measured responsivity for 533 nm is 0.12 A/W and agrees with the theoretical calculation for the
low
as
1
µ
A
at
a
reverse
bias
of
−0.5
V.
Light
at
a
533-nm
wavelength
is
incident
on
devices
with
different power; the photocurrent shows a nearly linear trend versus the light intensity (Figure 15b).
1 µ m-thick InP. To investigate the effect of bending on the device characteristics, the photo
different power;
the photocurrent
shows
a nearly linear
trend versus
the
intensity
(Figure 15b).
The measured
responsivity
for 533bending
nm
is 0.12
and agrees
with
the light
theoretical
calculation
for the
responsivities
under different
radiiA/W
are compared.
No
obvious
degradation
shows with
The measured responsivity for 533 nm is 0.12 A/W and agrees with the theoretical calculation for the
1 µm-thick
InP.
To
investigate
the
effect
of
bending
on
the
device
characteristics,
the
photo
responsivities
bending radii up to 38.1 mm, both for dark current and responsivity.
1 µ m-thick InP. To investigate the effect of bending on the device characteristics, the photo
under different bending radii are compared. No obvious degradation shows with bending radii up to
responsivities under different bending radii are compared. No obvious degradation shows with
38.1 mm,
both for dark current and responsivity.
bending radii up to 38.1 mm, both for dark current and responsivity.
(a)
(b)
Figure 15. Measured flexible InP p-i-n PD characteristics. (a) Measured dark current-voltage
characteristics. (b) Measured
(a) photocurrents at different incident optical
(b) powers for a 533-nm
wavelength light source (reprinted from [41]).
Figure 15. Measured flexible InP p-i-n PD characteristics. (a) Measured dark current-voltage
Figure 15. Measured flexible InP p-i-n PD characteristics. (a) Measured dark current-voltage
characteristics. (b) Measured photocurrents at different incident optical powers for a 533-nm
characteristics. (b) Measured photocurrents at different incident optical powers for a 533-nm
wavelength light source (reprinted from [41]).
wavelength light source (reprinted from [41]).
Photonics 2016, 3, 40
13 of 19
Photonics 2016, 3, 40
13 of 18
3.4. Silicon
Silicon NM-Based
NM-Based Flexible
Flexible Phototransistors
Phototransistors
3.4.
Compared to
the common
common p-n
p-n junction-based
junction-based photodetectors,
photodetectors, phototransistors
phototransistors have
have advantages
advantages
Compared
to the
in
terms
of
responsivity
and
quantum
efficiency.
It
has
been
reported
that
the
metal
in terms of responsivity and quantum efficiency. It has been reported that the metal oxide
oxide
semiconductor field-effect
field-effect transistors
transistors (MOSFETs)
(MOSFETs) show
in photosensitivity
photosensitivity
semiconductor
show outstanding
outstanding characteristics
characteristics in
and responsivity
Recently,
we demonstrated
a flexible
phototransistor
based onbased
single crystalline
and
responsivity[57].
[57].
Recently,
we demonstrated
a flexible
phototransistor
on single
silicon
NMs.
The
Si
NM
is
flip-transferred
on
flexible
substrate;
thus,
the
absorbing
Si areaSiisarea
not
crystalline silicon NMs. The Si NM is flip-transferred on flexible substrate; thus, the absorbing
limited
by the channel
dimension,
since the since
light is
notlight
as blocked
by blocked
the gate metal
the conventional
is
not limited
by the channel
dimension,
the
is not as
by theasgate
metal as the
phototransistors.
On
the
other
hand,
the
gate
electrode
beneath
the
detecting
Si
after
flip
transfer
acts
conventional phototransistors. On the other hand, the gate electrode beneath the detecting
Si after
as
a
high
reflection
mirror.
As
a
result,
our
proposed
structure
not
only
takes
advantage
of
the
higher
flip transfer acts as a high reflection mirror. As a result, our proposed structure not only takes
photo-sensing
ability,
butphoto-sensing
also further improves
thealso
light
absorption
due the
to more
area
and
advantage of the
higher
ability, but
further
improves
lightexposure
absorption
due
to
the
half
cavity
enhancement
effect.
more exposure area and the half cavity enhancement effect.
As shown
shown in
in Figure
Figure 16a,
16a, the
the device
device fabrication
fabrication process
process flow
flow starts
starts from
from partially
partially heavy
heavy n
n doping
doping
As
on aa p-type-doped
which
is later
deposited
withwith
metalmetal
to form
contacts
for source,
on
p-type-dopedSOI
SOIsubstrate,
substrate,
which
is later
deposited
to ohmic
form ohmic
contacts
for
drain
and
gate,
respectively
(Figure
16c).
Before
the
metal
e-beam
evaporation,
a
typical
NM
release
source, drain and gate, respectively (Figure 16c). Before the metal e-beam evaporation, a typical NM
process
is employed
to maketo
the
Si NM
to ready
be picked
by PET
with an adhesive
release process
is employed
make
theready
Si NM
to beup
picked
upsubstrate
by PET substrate
with an
layer
(Figure
16d).
Furthermore,
an
anti-reflection
layer
(SU-8
2002)
is
coated
on
top
of
flipped
adhesive layer (Figure 16d). Furthermore, an anti-reflection layer (SU-8 2002) is coated on Si
topNM
of
to
improve
the
light
absorption
efficiency.
The
finished
phototransistor
on
flexible
PET
substrate
is
flipped Si NM to improve the light absorption efficiency. The finished phototransistor on flexible PET
shown in is
theshown
microscopic
image as Figure
16f.
substrate
in the microscopic
image
as Figure 16f.
Figure 16. The schematic illustration of the device fabrication process flow. (a) Beginning with
Figure 16. The schematic illustration of the device fabrication process flow. (a) Beginning with forming
forming n+ regions by ion implantation of source/drain regions to achieve an ohmic contact.
n+ regions by ion implantation of source/drain regions to achieve an ohmic contact. (b) Releasing Si
(b) Releasing Si NM by selective etching of a buried oxide layer. (c) Metallization by e-beam
NM by selective etching of a buried oxide layer. (c) Metallization by e-beam evaporation to deposit
evaporation
deposit source/drain
electrodes
and adielectric.
stack of gate/gate
dielectric.
(d) Transfer
printing
source/draintoelectrodes
and a stack
of gate/gate
(d) Transfer
printing
fully-fabricated
fully-fabricated
devices
to
adhesive
layer-coated
PET
substrate.
(e)
Spin-coating
a
protection
on
devices to adhesive layer-coated PET substrate. (e) Spin-coating a protection layer on top of thelayer
surface.
topMicroscopic
of the surface.
(f) Microscopic
of phototransistor.
a finished flexible
phototransistor.
Insets
in (c,e) depict
(f)
image
of a finishedimage
flexible
Insets
in (c,e) depict
the cross-sectional
the
cross-sectional
view
of
device
(reprinted
from
[25]).
view of device (reprinted from [25]).
The gate channel is 50 µ m wide and 2 µ m long, and the thickness of Si NM is 270 nm. Dark
The gate channel is 50 µm wide and 2 µm long, and the thickness of Si NM is 270 nm. Dark
current and photocurrent with red (632 nm), green (532 nm) and blue (473 nm) laser illuminations
current and photocurrent with red (632 nm), green (532 nm) and blue (473 nm) laser illuminations are
are measured under two scenarios; one is under low gate bias to obtain a high photo-to-dark current
measured under two scenarios; one is under low gate bias to obtain a high photo-to-dark current ratio,
ratio, and the other is under relatively high gate voltage to achieve high responsivity. For the first
and the other is under relatively high gate voltage to achieve high responsivity. For the first operation
operation condition, the phototransistor yields5 up to a 105 photo-to-dark ratio under 0.5 V for VGS and
condition, the phototransistor yields up to a 10 photo-to-dark ratio under 0.5 V for VGS and 0.05 V for
0.05 V for VDS, while the responsivity only shows 0.04 A/W due to the very thin Si NM
used for the
V DS , while the responsivity only shows 0.04 A/W due to the very thin Si NM used for the absorption
absorption gating layer. As gate bias increased to 1 V, the photo-to-dark ratio drops to 11, but the
gating layer. As gate bias increased to 1 V, the photo-to-dark ratio drops to 11, but the drain current
drain current increase significantly, as shown in Figure 17b. The responsivity at a voltage bias of
increase significantly, as shown in Figure 17b. The responsivity at a voltage bias of V GS = 1 V and
VGS = 1 V and VDS = 3 V is calculated to be 51, 41 and 18 A/W under red, green and blue
incident
V DS = 3 V is calculated to be 51, 41 and 18 A/W under red, green and blue incident light, respectively.
light, respectively.
To investigate the effects of metal reflector and anti-reflection coating on the light absorption
enhancement, three cases shown as in Figure 17c are simulated with regard to the optical properties
in the 400–700-nm visible wavelength range. The simulation shows that the average absorption
percentage
Si NM with the reflector and anti-reflection layer is increased more than twice14from
Photonics 2016,in
3, 40
of 19
20.2%–48%, compared to Si NM directly on PET substrate.
Figure
Drain current-gate
current-gate voltage
voltage characteristics
characteristics (I
(IDS
DS-V
) at VDS = 0 V. The inset shows the
Figure 17.
17. (a)
(a) Drain
-VGS
GS ) at V DS = 0 V. The inset shows the
magnified
(b) Drain
Drain current-drain
current-drain voltage
voltagecharacteristics
characteristics(I(IDS
DS-V
-VGS
) under dark
magnified plot
plot of
of photo
photo currents.
currents. (b)
GS ) under dark
and
illumination
with
various
light
sources
(red,
green
and
blue)
onto
flexible
phototransistors.
and illumination with various light sources (red, green and blue) onto flexible phototransistors. The
The
IDS
-Vcurve
GS curve
under
= for
1 Vthe
forphoto-to-dark
the photo-to-dark
ratio as
shows
as «1
high
as5 .≈1
105.
IDS -V
under
V GS V
=GS1 V
currentcurrent
ratio shows
high as
ˆ 10
(c)×(Left)
GS
(c)
(Left)
Three
layer structures
used to
the lightofabsorption
of Siand
NM,
(right)
and their
Three
layer
structures
used to simulate
thesimulate
light absorption
Si NM, (right)
their
corresponding
corresponding
simulated
absorption
of Si NM:
without
any layers;
(ii) reflector
with the underneath
metal reflector
simulated absorption
of Si
NM: (i) without
any(i)
layers;
(ii) with
the metal
the
underneath
NM;
(iii) with
the metal
reflector
Si NM
SU-8
layer
onNM,
the
Si NM; (iii) the
withSithe
metal
reflector
underneath
theunderneath
Si NM andthe
SU-8
ARCand
layer
on ARC
the top
of Si
top
of Si NM, The
respectively.
Thedenotes
dashedblue
line (473
denotes
(473
nm),
green
nm) and
(632 nm)
respectively.
dashed line
nm),blue
green
(532
nm)
and(532
red (632
nm) red
wavelengths
wavelengths
(reprinted
(reprinted from
[25]). from [25]).
Devices
with different
Si NM
channel
active and
areaanti-reflection
dimensions arecoating
also fabricated
andabsorption
measured
To investigate
the effects
of metal
reflector
on the light
to
explore
the
influences;
the
larger
width/length
ratio
shows
higher
photo
responsivity.
Under
enhancement, three cases shown as in Figure 17c are simulated with regard to the optical properties
bending
at curvaturevisible
radii ofwavelength
15 mm, the range.
device isThe
proven
to be stable
in terms
of responsivity,
which
in the 400–700-nm
simulation
shows
that the
average absorption
provides
great
promises
for
flexible
photodetecting
applications.
percentage in Si NM with the reflector and anti-reflection layer is increased more than twice from
20.2%–48%, compared to Si NM directly on PET substrate.
3.5. Flexible Photodetecting P-N Diode between Pentacene and Si NM
Devices with different Si NM channel active area dimensions are also fabricated and measured to
Besides
stack between
various
inorganicratio
semiconductor
the heterogeneous
p-n
explore
the influences;
the larger
width/length
shows highermaterials,
photo responsivity.
Under bending
junction
between
andthe
inorganic
has
been
by transfer
printing.
It
at curvature
radii organic
of 15 mm,
device ismaterial
proven to
bealso
stable
in demonstrated
terms of responsivity,
which
provides
is
reported
in [42]
that anphotodetecting
n-doped single
crystal Si NM, which is transfer printed on a plastic
great
promises
for flexible
applications.
substrate, forms a heterogeneous p-n diode with a p-doped pentacene. Figure 18a is the microscopic
3.5. Flexible
Photodetecting
Diode between
Pentacene
Si NM
picture
of the
Si NM with aP-N
hexagonal
meshed
pattern and
on PET
substrate, partly covered by Au metal.
The pentacene
is
on
the
right
side
of
the
Si
NM,
as
shown
in
Figurethe
18b.
The verticalp-n
p-njunction
diode
Besides stack between various inorganic semiconductor materials,
heterogeneous
structure
can be clearly
seen in the
inset schematic
drawing.
The scanning
electron
microscopy
(SEM)
between organic
and inorganic
material
has also been
demonstrated
by transfer
printing.
It is reported
image
of
the
device
is
shown
in
Figure
18c,
and
atomic
force
microscopy
(AFM)
shows
the
pentacene
in [42] that an n-doped single crystal Si NM, which is transfer printed on a plastic substrate, forms a
surface
with anp-n
average
of 180 pentacene.
nm.
heterogeneous
diodegrain
with size
a p-doped
Figure 18a is the microscopic picture of the Si NM
with a hexagonal meshed pattern on PET substrate, partly covered by Au metal. The pentacene is on
the right side of the Si NM, as shown in Figure 18b. The vertical p-n diode structure can be clearly seen
in the inset schematic drawing. The scanning electron microscopy (SEM) image of the device is shown
in Figure 18c, and atomic force microscopy (AFM) shows the pentacene surface with an average grain
size of 180 nm.
Photonics 2016, 3, 40
15 of 19
Photonics 2016, 3, 40
15 of 18
Figure 18. (a) Microscopic image of transferred Si NM grid on PET substrate. (b) Microscopic images
of Si NM (left)/pentacene (right) heterojunction. The inset shows the cross-section of the
heterostructure. (c) SEM image of Si NM and deposited pentacene layer sitting on SU-8-coated PET
substrate. The inset shows the detailed layer structure. (d) AFM image of deposited pentacene on Si
NM. The average pentacene grain size is 180 nm (reprinted from [42]).
The I-V characteristics of the Si-pentacene p-n diode are measured, showing a good rectifying
Figure 18. (a) Microscopic image of transferred Si NM grid on PET substrate. (b) Microscopic images
Figurewith
18. (a)
Microscopic
image
transferred
Si NM grid
on PET
substrate.
(b) Microscopic
of hole
behavior
ideality
factor
n = of
1.89.
The relatively
high
series
resistance
is due to images
the low
of Si NM (left)/pentacene (right) heterojunction. The inset shows the cross-section of the
Si
NM
(left)/pentacene
(right)
heterojunction.
The
inset
shows
the
cross-section
of
the
heterostructure.
mobility for pentacene and the possible presence of native oxide. The photodetecting characteristics
heterostructure.
SEMand
image
of Si NM
and deposited
pentacene
layer sitting
SU-8-coated
PET
SEM image
of (c)
Si NM
deposited
pentacene
layermeasured,
sitting
on SU-8-coated
PETon
substrate.
The inset
with(c)different
incident
light wavelengths
are also
and it shows
photo responsivity
of
substrate.
The
inset
shows
the
detailed
layer
structure.
(d)
AFM
image
of
deposited
pentacene
on
Si
showsfor
the532-nm
detailedillumination.
layer structure.The
(d) external
AFM image
of deposited
pentacene
on Si NM. to
Thebeaverage
0.7 A/W
quantum
efficiency
is calculated
21.9% at a
NM. The average
pentacene
grain
size is 180
nm
(reprinted from [42]).
pentacene
grain size
is 180
nm
(reprinted
from
[42]).
632-nm
laser illumination,
which
is the highest
over 473–905 nm. The effects of mechanical flexibility
on device
performances
are also
examined.
Figure
19diode
showsare
themeasured,
I-V characteristics
Si-pentacene
The I-V
characteristics
of the
Si-pentacene
p-n
showingofa the
good
rectifying
The
I-V
characteristics
of
the
Si-pentacene
p-n
diode
are
measured,
showing
a
good
rectifying
diode under
different
77.5 mm
to resistance
15 mm, which
indicates
behavior
with
idealityconvex
factor bending
n = 1.89.radii
The from
relatively
highdown
series
is due
to the not
lowmuch
hole
behavior
withThe
ideality
factor n versus
= 1.89.bending
The relatively
high
seriesasresistance
is due19b,
to the
low hole
degradation.
photocurrent
strain
is
depicted,
well,
in
Figure
showing
that
mobility for pentacene and the possible presence of native oxide. The photodetecting characteristics
mobility
for pentacene
and the possible
presence
offrom
native
oxide.
The aphotodetecting
characteristics
the
external
quantum
efficiency
increases
to
25.1%
21.9%
under
bending
strain
of
1.08%.
with different incident light wavelengths are also measured, and it shows photo responsivity of
with To
different incident
light
are also measured, and
and external
it showsquantum
photo responsivity
of
causewavelengths
for this
efficiency,
0.7 A/Winvestigate
for 532-nmthe
illumination.
Theimproved
external photocurrent
quantum efficiency
is calculated to be
21.9% atthe
a
0.7
A/Wconfocal
for 532-nm
illumination.
The
external quantum
efficiency
is calculated
toisbefound
21.9%
at a
Raman
microscope
is used
to reflect
strain
effect
of the
materials.
It
under
632-nm
laser illumination,
which
is the
highestthe
over
473–905
nm.
Thetwo
effects
of mechanical
flexibility
632-nm
laser illumination,
which
is the highest
over 473–905
nm. The
effects
of mechanical
tensile
strain
that the three
vibration
mode
peaks
of pentacene
have
shifted
under
theflexibility
bending
on
device
performances
are also
examined.
Figure
19 shows
the I-V characteristics
of the Si-pentacene
on
device
performances
are
also
examined.
Figure
19
shows
the
I-V
characteristics
of
the
Si-pentacene
condition.
According
to the study
thatradii
the Raman
peak
is related
to the
mobility
improvement
diode
under
different convex
bending
from 77.5
mmshift
down
to 15 mm,
which
indicates
not much
diode
under different
convex
bending radii
from 77.5under
mm down
to 15 mm,
which indicates
much
of
pentacene
[58,59],
this
photocurrent
enhancement
the
bending
condition
could
be not
explained
degradation. The photocurrent versus bending strain is depicted, as well, in Figure 19b, showing
that
degradation.
The
photocurrent
versus
bending
strain
is
depicted,
as
well,
in
Figure
19b,
showing
that
by the
mobility
improvement,
given
that tensile
strain
on21.9%
the crystal
lattice
could strain
increase
carriers’
the
external
quantum
efficiency
increases
to 25.1%
from
under
a bending
of the
1.08%.
the
external
quantum
efficiency
increases to 25.1% from 21.9% under a bending strain of 1.08%.
mobility
of Si
NM, as
[6,60].
To investigate
thewell
cause
for this improved photocurrent and external quantum efficiency, the
Raman confocal microscope is used to reflect the strain effect of the two materials. It is found under
tensile strain that the three vibration mode peaks of pentacene have shifted under the bending
condition. According to the study that the Raman peak shift is related to the mobility improvement
of pentacene [58,59], this photocurrent enhancement under the bending condition could be explained
by the mobility improvement, given that tensile strain on the crystal lattice could increase the carriers’
mobility of Si NM, as well [6,60].
Figure 19. Characterizations Si NM-pentacene diode under mechanical bending. (a) Measured
Figure 19. Characterizations Si NM-pentacene diode under mechanical bending. (a) Measured
photocurrent of the diode under different bending strains. (b) Plot of photocurrent change as a
photocurrent of the diode under different bending strains. (b) Plot of photocurrent change as a
function of
of strain.
strain. (c)
(c) An
An optical
optical image
image of
of the
the diode
diode under
underbending
bending(reprinted
(reprintedfrom
from[42]).
[42]).
function
To investigate the cause for this improved photocurrent and external quantum efficiency, the
Raman confocal microscope is used to reflect the strain effect of the two materials. It is found under
Figure
19.that
Characterizations
Si NM-pentacene
diode
under mechanical
bending.
(a) Measured
tensile
strain
the three vibration
mode peaks
of pentacene
have shifted
under
the bending
photocurrent of the diode under different bending strains. (b) Plot of photocurrent change as a
function of strain. (c) An optical image of the diode under bending (reprinted from [42]).
Photonics 2016, 3, 40
16 of 19
condition. According to the study that the Raman peak shift is related to the mobility improvement of
pentacene [58,59], this photocurrent enhancement under the bending condition could be explained by
the mobility improvement, given that tensile strain on the crystal lattice could increase the carriers’
mobility of Si NM, as well [6,60].
Due to thickness of only 340 nm and meshed hexagonal pattern, the Si NM and pentacene
heterojunction structure on PET is highly transparent for visible light, as Figure 8c shows. Thus, an
optically-transparent, photosensitive and flexible heterogeneous p-n diode between organic pentacene
and inorganic Si NM is demonstrated based on transfer printing, extending the boundary of the
transfer printing technique to even broader material choices.
4. Conclusions and Outlooks
In summary, transfer printing has provided a practical approach to hybrid integration of a
large variety of materials with different electrical and optical characteristics to achieve versatile
and high performance optoelectronic systems. The III-V group gain material and photon sensing
Ge on Si substrate by transfer printing approach offers tremendous application potentials on a
CMOS-compatible silicon photonics platform. Moreover, the bendable inorganic single-crystal
semiconductor NM has also been enabled, which makes possible the integrated optoelectronics
in flexibility-required applications, such as wearable devices and second skin. At the same time,
the heterogeneous p-n diode formed by transfer printing with good electronic behavior also indicates
that this technique is not limited to the applications just in mechanical bonding between different
materials, but also provides infinite possibilities to form arbitrary heterojunctions with various
combinations of materials.
Acknowledgments: The work was supported by AFOSR under grants: FA9550-11-C-0026, FA9550-09-1-0482,
FA9550-09-C-0200, FA9550-08-1-0337, by ARO under Grant W911NF-09-1-0505 and by NSF under Grant
ECCS-1308520.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
Rogers, J.A.; Lagally, M.G.; Nuzzo, R.G. Synthesis, assembly and applications of semiconductor
nanomembranes. Nature 2011, 477, 45–53. [CrossRef] [PubMed]
Hwang, S.W.; Tao, H.; Kim, D.H.; Cheng, H.; Song, J.K.; Rill, E.; Brenckle, M.A.; Panilaitis, B.; Won, S.M.;
Kim, Y.S.; et al. A physically transient form of silicon electronics. Science 2012, 337, 1640–1644. [CrossRef]
[PubMed]
Schmidt, O.G.; Eberl, K. Nanotechnology: Thin solid films roll up into nanotubes. Nature 2001, 410, 168.
[CrossRef] [PubMed]
Trotta, R.; Atkinson, P.; Plumhof, J.; Zallo, E.; Rezaev, R.; Kumar, S.; Baunack, S.; Schröter, J.; Rastelli, A.;
Schmidt, O. Nanomembrane quantum light emitting diodes integrated onto piezoelectric actuators.
Adv. Mater. 2012, 24, 2668–2672. [CrossRef] [PubMed]
Li, X. Self-rolled-up microtube ring resonators: A review of geometrical and resonant properties.
Adv. Opt. Photonic 2011, 3, 366–387. [CrossRef]
Scott, S.A.; Lagally, M.G. Elastically strain-sharing nanomembranes: Flexible and transferable strained silicon
and silicon-germanium alloys. J. Phys. D Appl. Phys. 2007, 40, R75–R92. [CrossRef]
Yuan, H.C.; Ma, Z.; Roberts, M.M.; Savage, D.E.; Lagally, M.G. High-speed strained-single-crystal-silicon
thin-film transistors on flexible polymers. J. Appl. Phys. 2006, 100. [CrossRef]
Sun, L.; Qin, G.; Seo, J.H.; Celler, G.K.; Zhou, W.; Ma, Z. 12 GHz thin film transistors on transferrable silicon
nanomembranes for high performance flexible electronics (cover story). Small 2010, 6, 2553–2557. [CrossRef]
[PubMed]
Zhang, K.; Seo, J.H.; Zhou, W.; Ma, Z. Fast flexible electronics using transferrable silicon nanomembranes
(topical review). J. Phys. D Appl. Phys. 2012, 45. [CrossRef]
Photonics 2016, 3, 40
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
17 of 19
Zhou, W.; Ma, Z.; Yang, H.; Qiang, Z.; Qin, G.; Pang, H.; Chen, L.; Yang, W.; Chuwongin, S.; Zhao, D. Flexible
photonic-crystal fano filters based on transferred semiconductor nanomembranes. J. Phys. D Appl. Phys.
2009, 42. [CrossRef]
Zhou, W.; Ma, Z.; Yang, H.; Chen, L.; Yang, W.; Qiang, Z.; Qin, G.; Pang, H.; Chuwongin, S.; Zhao, D.
Semiconductor nanomembranes for stacked and flexible photonics. In Proceedings of the International
Society for Optics and Photonics, San Francisco, CA, USA, 23 January 2010; p. 76060U.
Yang, H.; Zhao, D.; Chuwongin, S.; Seo, J.H.; Yang, W.; Shuai, Y.; Berggren, J.; Hammar, M.; Ma, Z.; Zhou, W.
Transfer-printed stacked nanomembrane lasers on silicon. Nat. Photonic 2012, 6, 615–620. [CrossRef]
Zhou, H.; Seo, J.-H.; Paskiewicz, D.M.; Zhu, Y.; Celler, G.K.; Voyles, P.M.; Zhou, W.; Lagally, M.G.; Ma, Z.
Fast flexible electronics with strained silicon nanomembranes. Sci. Rep. 2013, 3. [CrossRef] [PubMed]
Meitl, M.A.; Zhu, Z.T.; Kumar, V.; Lee, K.J.; Feng, X.; Huang, Y.Y.; Adesida, I.; Nuzzo, R.G.; Rogers, J.A.
Transfer printing by kinetic control of adhesion to an elastomeric stamp. Nat. Mater. 2006, 5, 33–38. [CrossRef]
Harazim, S.M.; Quinones, V.A.B.; Kiravittaya, S.; Sanchez, S.; Schmidt, O. Lab-in-a-tube: On-chip integration
of glass Optofluidic Ring Resonators for label-free Sensing Applications. Lab Chip 2012, 12, 2649–2655.
[CrossRef] [PubMed]
Song, Y.M.; Xie, Y.; Malyarchuk, V.; Xiao, J.; Jung, I.; Choi, K.-J.; Liu, Z.; Park, H.; Lu, C.; Kim, R.-H. Digital
cameras with designs inspired by the arthropod eye. Nature 2013, 497, 95–99. [CrossRef] [PubMed]
Zhou, W.; Ma, Z. Breakthroughs in nanomembranes and nanomembrane lasers. IEEE Photonic J. 2013, 5.
[CrossRef]
Zhou, W.; Zhao, D.; Shuai, Y.-C.; Yang, H.; Chuwongin, S.; Chadha, A.; Seo, J.-H.; Wang, K.X.; Liu, V.; Ma, Z.
Progress in 2D photonic crystal Fano resonance photonics. Prog. Quantum Electron. 2014, 38, 1–74. [CrossRef]
Hu, J.; Li, L.; Lin, H.; Zhang, P.; Zhou, W.; Ma, Z. Flexible integrated photonics: Where materials, mechanics
and optics meet (invited). Opt. Mater. Express 2013, 3, 1313–1331. [CrossRef]
Roberts, M.M.; Klein, L.J.; Savage, D.E.; Slinker, K.A.; Friesen, M.; Celler, G.; Eriksson, M.A.; Lagally, M.G.
Elastically relaxed free-standing strained-silicon nanomembranes. Nat. Mater. 2006, 5, 388–393. [CrossRef]
[PubMed]
Rogers, J.A.; Someya, T.; Huang, Y. Materials and mechanics for stretchable electronics. Science 2010, 327,
1603–1607. [CrossRef] [PubMed]
Janglin, C.; Liu, C.T. Technology advances in flexible displays and substrates. IEEE Access 2013, 1, 150–158.
[CrossRef]
Ko, H.; Takei, K.; Kapadia, R.; Chuang, S.; Fang, H.; Leu, P.W.; Ganapathi, K.; Plis, E.; Kim, H.S.; Chen, S.-Y.
Ultrathin compound semiconductor on insulator layers for high-performance nanoscale transistors. Nature
2010, 468, 286–289. [CrossRef] [PubMed]
Chen, Y.; Li, H.; Li, M. Flexible and tunable silicon photonic circuits on plastic substrates. Sci. Rep. 2012, 2.
[CrossRef] [PubMed]
Seo, J.H.; Zhang, K.; Kim, M.; Zhao, D.; Yang, H.; Zhou, W.; Ma, Z. Flexible phototransistors based on
single-crystalline silicon nanomembranes. Adv. Opt. Mater. 2015, 4. [CrossRef]
Seo, J.-H.; Zhang, Y.; Yuan, H.-C.; Wang, Y.; Zhou, W.; Ma, J.; Ma, Z.; Qin, G. Investigation of various
mechanical bending strains on characteristics of flexible monocrystalline silicon nanomembrane diodes on a
plastic substrate. Microelectron. Eng. 2013, 110, 40–43. [CrossRef]
Gao, L.; Zhang, Y.; Malyarchuk, V.; Jia, L.; Jang, K.-I.; Webb, R.C.; Fu, H.; Shi, Y.; Zhou, G.; Shi, L. Epidermal
photonic devices for quantitative imaging of temperature and thermal transport characteristics of the skin.
Nat. Commun. 2014, 5. [CrossRef] [PubMed]
Huang, C.C.; Wu, X.; Liu, H.; Aldalali, B.; Rogers, J.A.; Jiang, H. Large-field-of-view wide-spectrum artificial
reflecting superposition compound eyes. Small 2014, 10, 3050–3057. [CrossRef] [PubMed]
Xu, X.; Subbaraman, H.; Kwong, D.; Hosseini, A.; Zhang, Y.; Chen, R.T. Large area silicon nanomembrane
photonic devices on unconventional substrates. IEEE Photonic Technol. Lett. 2013, 25, 1601–1604. [CrossRef]
Zhao, D.; Liu, S.-C.; Yang, H.; Ma, Z.; Carl, R.-H.; Mattias, H.; Zhou, W. Printed Large-Area Single-Mode
Photonic Crystal Bandedge Surface-Emitting Lasers on Silicon. Sci. Rep. 2016, 6, 18860. [CrossRef] [PubMed]
Yang, H.; Zhao, D.; Liu, S.; Liu, Y.; Seo, J.-H.; Ma, Z.; Zhou, W. Transfer Printed Nanomembranes for
Heterogeneously Integrated Membrane Photonics. Photonics 2015, 2, 1081–1100. [CrossRef]
Photonics 2016, 3, 40
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
18 of 19
Xu, X.; Subbaraman, H.; Chakravarty, S.; Hosseini, A.; Lin, C.-Y.; Kwong, D.; Chen, R.T. Stamp printing
of silicon-nanomembrane-based photonic devices onto flexible substrates with a suspended configuration.
Opt. Lett. 2012, 37, 1020–1022. [CrossRef] [PubMed]
Xu, X.; Subbaraman, H.; Chakravarty, S.; Hosseini, A.; Covey, J.; Yu, Y.; Chen, R.T. Flexible single-crystal
silicon nanomembrane photonic crystal cavity. ACS Nano 2014, 8, 12265–12271. [CrossRef] [PubMed]
Yang, H.; Zhao, D.; Seo, J.-H.; Chuwongin, S.; Kim, S.; Rogers, J.A.; Ma, Z.; Zhou, W. Broadband membrane
reflectors on glass. IEEE Photonic Technol. Lett. 2012, 24, 476–478. [CrossRef]
Yang, H.; Pang, H.; Qiang, Z.; Ma, Z.; Zhou, W. Surface-normal fano filters based on transferred silicon
nanomembranes on glass substrates. Electron. Lett. 2008, 44, 858–859. [CrossRef]
Qiang, Z.; Yang, H.; Chen, L.; Pang, H.; Ma, Z.; Zhou, W. Fano filters based on transferred silicon
nanomembranes on unconventional substrates. IEEE Photonic Technol. Lett. 2013, 25, 1601–1604.
Jung, Y.; Chang, T.-H.; Zhang, H.; Yao, C.; Zheng, Q.; Yang, V.; Mi, H.; Kim, M.; Cho, S.-J.; Park, D.-W.; et al.
High-performance green flexible electronics based on biodegradable cellulose nanofibril paper. Nat. Commun.
2015, 6, 7170. [CrossRef] [PubMed]
Justice, J.; Bower, C.; Meitl, M.; Mooney, M.; Gubbins, M.; Corbett, B. Wafer-scale integration of group III-V
lasers on silicon using transfer printing of epitaxial layers. Nat. Photonic 2012, 6, 610–614. [CrossRef]
Menon, L.; Yang, H.; Cho, S.-J.; Mikael, S.; Ma, Z.; Carl, R.-H.; Mattias, H.; Zhou, W. Heterogeneously
Integrated InGaAs and Si Membrane Four-Color Photodetector Arrays. IEEE Photonics J. 2016, 8, 1–7.
[CrossRef]
Cho, M.; Seo, J.-H.; Kim, M.; Lee, J.; Liu, D.; Zhou, W.; Yu, Z.; Ma, Z. Resonant cavity germanium
photodetector via stacked single-crystalline nanomembranes. JVSTB 2016, 34. [CrossRef]
Yang, W.; Yang, H.; Qin, G.; Ma, Z.; Berggren, J.; Hammar, M.; Soref, R.; Zhou, W. Large-area InP-based
crystalline nanomembrane flexible photodetectors. Appl. Phys. Lett. 2010, 96. [CrossRef]
Seo, J.-H.; Oh, T.-Y.; Park, J.; Zhou, W.; Ju, B.-K.; Ma, Z. A Multifunction Heterojunction Formed between
Pentacene and a Single-Crystal Silicon Nanomembrane. Adv. Funct. Mater. 2013, 23, 3398–3403. [CrossRef]
Xia, Z.; Song, H.; Kim, M.; Zhou, M.; Chang, T.; Liu, D.; Xiong, K.; Yu, Z.; Ma, Z.; Gan, Q. Photodetecting
MOSFET based on ultrathin single-crystal germanium nanomembrane. In Proceedings of Conference on
Lasers and Electro-Optics: Science and Innovations 2016, San Jose, CA, USA, 5–10 June 2016.
Seo, J.-H.; Li, J.; Lee, J.; Lin, J.; Jiang, H.; Ma, Z. A simplified method of making flexible blue LEDs on a
plastic substrate. IEEE Photonic 2015, 7. [CrossRef]
Chen, R.; Tran, T.-T.D.; Ng, K.; Ko, W.; Chuang, L.; Sedgwick, F.; Chang-Hasnain, C. Nanolasers grown on
silicon. Nat. Photonic 2011, 5, 170–175. [CrossRef]
Fang, A.W.; Cohen, O.; Jones, R.; Paniccia, M.J.; Bowers, J.E. Design and fabrication of optically pumped
hybrid silicon-AlGaInAs evanescent lasers. IEEE J. Sel. Top. Quantum Electron. 2006, 12, 1657–1663.
Fang, A.W.; Park, H.; Cohen, O.; Jones, R.; Paniccia, M.J.; Bowers, J.E. Electrically pumped hybrid
AlGaInAs-silicon evanescent laser. Opt. Express 2006, 14, 9203–9210. [CrossRef] [PubMed]
Vecchi, G.; Raineri, F.; Sagnes, I.; Yacomotti, A.; Monnier, P.; Karle, T.J.; Lee, K.-H.; Braive, R.; Gratiet, L.;
Guilet, S.; et al. Continuous-wave operation of photonic band-edge laser near 1.55 µm on silicon wafer.
Opt. Express 2007, 15, 7551–7556. [CrossRef] [PubMed]
Hirose, K.; Liang, Y.; Kurosak, Y.; Watanabe, A.; Sugiyama, T.; Noda, S. Watt-class high-power,
high-beam-quality photonic-crystal lasers. Nat. Photonic 2014, 8, 406–411. [CrossRef]
Noda, S.; Yokoyama, M.; Imada, M.; Chutinan, A.; Mochizuki, M. Polarization mode control of
two-dimensional photonic crystal laser by unit cell structure design. Science 2001, 293, 1123–1125. [CrossRef]
[PubMed]
Miyai, E.; Sakai, K.; Okano, T.; Kunishi, W.; Ohnishi, D.; Noda, S. Photonics: Lasers producing tailored
beams. Nature 2006, 441, 946–946. [CrossRef] [PubMed]
Dosunmu, O.I.; Cannon, D.D.; Emsley, M.K.; Ghyselen, B.; Liu, J.; Kimerling, L.C.; Unlu, M. Resonant
Cavity Enhanced Ge Photodetectors for 1550 nm Operation on Reflecting Si Substrates. IEEE J. Sel. Top.
Quantum Electron. 2004, 10, 694–701. [CrossRef]
Tsagaris, V.; Anastassopoulos, V. Fusion of visible and infrared imagery for night color vision. Displays 2005,
26, 191–196. [CrossRef]
Menon, L.; Yang, H.; Cho, S.; Mikael, S.; Ma, Z.; Zhou, W. Transferred flexible three-color silicon membrane
photodetector arrays. IEEE Photonic J. 2015, 7, 1–6. [CrossRef]
Photonics 2016, 3, 40
55.
56.
57.
58.
59.
60.
19 of 19
Michel, B.; Bernard, A.; Andre-Jacques, A.-H. Smart-Cut: A New Silicon on Insulator Material Technology
Based on Hydrogen Implantation and Wafer Bonding. Jpn. J. Appl. Phys. 1997, 36, 1636–1641.
Chen, L.; Qiang, Z.; Yang, H.; Pang, H.; Ma, Z.; Zhou, W. Polarization and angular dependent transmissions
on transferred nanomembrane Fano filters. Opt. Express 2009, 17, 8396–8406. [CrossRef] [PubMed]
Hamilton, M.C.; Martin, S.; Kanicki, J. Thin-Film Organic Polymer Phototransistors. IEEE Trans.
Electron. Devices 2004, 51, 877–885. [CrossRef]
Cheng, H.L.; Liang, X.W.; Chou, W.Y.; Mai, Y.S.; Yang, C.Y.; Chang, L.R.; Tang, F.C. Raman spectroscopy
applied to reveal polycrystalline grain structures and carrier transport properties of organic semiconductor
films: Application to pentacene-based organic transistors. Org. Electron. 2009, 10, 289–298. [CrossRef]
Cheng, H.L.; Chou, W.Y.; Kuo, C.W.; Tang, F.C.; Wang, Y.W. Electric field-induced structural changes in
pentacene-based organic thin-film transistors studied by in situ micro-Raman spectroscopy. Appl. Phys. Lett.
2006, 88. [CrossRef]
Peng, C.-Y.; Huang, C.-F.; Fu, Y.-C.; Yang, Y.-H.; Lai, C.-Y.; Chang, S.-T.; Liu, C.W. Comprehensive study of
the Raman shifts of strained silicon and germanium. J. Appl. Phys. 2009, 105. [CrossRef]
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