Uncooled Infrared Photon Detection
Concepts and Devices
Viraj Jayaweera Piyankarage
Department of Physics & Astronomy
Georgia State University
Outline
•
Introduction
•
Infrared Detectors based on
1. Dye-Sensitization of Nanostructured Semiconductors
• Dye-sensitized NIR detector design, experimental results, and conclusion
• 1/f Noise on DS nano structures
2. Displacement Currents in Semiconductor Quantum Dots (QDs)
Embedded Dielectric Media
• Size quantization effects
• QD capacitor based detector design, experimental results, and conclusion
3. Split-off Band Transitions in GaAs/AlGaAs Heterojunctions
• High operating temperature split-off response observed from HEIWIP design for
17μm threshold wavelength
• Uncooled split-off band detector design Experimental results, and conclusion
4. Free Carrier Absorption in GaSb Homojunctions
• GaSb HIWIP detector design, experimental results, and conclusion
•
Future Work
2
Electromagnetic Spectrum
http://www.nasa.gov/centers/langley/science
Visible
Near-IR
Mid-IR
0.8 – 5 m
5 - 30 m
Wavelength
3
Far-IR
Micro Wave
30 - 300 m
IR Wavelength Range Classification
–
–
–
–
–
–
1-3 μm
3-5 μm
5-14 μm
14-30 μm
30-100 μm
100-1000 μm
Short Wavelength Infrared
Medium Wavelength Infrared
Long Wavelength Infrared
Very Long Wavelength Infrared
Far Infrared
Sub-millimeter
4
SWIR
MWIR
LWIR
VLWIR
FIR
SubMM
Applications
http://www.netcast.com.hk/Products.htm
Infrared Body
Temperature
Thermometer
Remote controller and receiver
Visible Light
Infrared
5
Applications
Blood Flow
brain imaging
www.medphys.ucl.ac.uk/research/borl/
Transverse, coronal, and sagittal views
across the 3D absorption image of the infant,
acquired at 780 nm.
Human suspect climbing
over a fence at 2:49 AM in
total darkness
Night vision
helmet
Infrared image of Orion
6
Applications
Thermal analysis of a
fluid tank level detection
www.x20.org
Close up image of a Intel Celeron chip
ºF
www.x20.org
Faulty connection at power station
7
Bad Insulation spots
Different Types of Infrared Detectors
IR Detectors
Photon
Photoconductive
Thermal
Bolometric
Photovoltaic
Thermoelectric
Pyroelectric
Photoemissive
8
Dye-Sensitized Near-Infrared Detectors
(DSNID)
9
Direct and Sensitized Photo-Injection
CB
CB
LUMO
HOMO
VB
VB
Semiconductor
Light induced charge
carrier generation in a
semiconductor
Dye
Dye-sensitized electron
injection to a semiconductor
LUMO = Lowest Unoccupied Molecular Orbital
HOMO = Highest Occupied Molecular Orbital
10
Dye-Sensitized Near-Infrared Detectors
(DSNID)
n-TiO2
p-CuSCN
nanoparticles
dye CuSCN
p-type
n-type
TiO2DyeIRDye
V
Solid State Device (No Liquid Electrolyte)
11
Structure of a dye-sensitized IR Detector
CTO
Transparent
Conducting Tin
Oxide (CTO)
TiO2 nanoparticles
Glass
n-TiO2
Dye
Glass
Platinum or
Gold layer
p-CuSCN
Appl. Phys. Lett., Vol. 85, No. 23, (2004)
12
Energy Level Diagram: n/D/p - Heterojunction
-1
Vacuum
Energy (eV)
CB
-2
-3
-4
S*
CB
-5
VB
S0
-6
-7
-8
VB
n-TiO2
Dye
p-CuSCN
Appl. Phys. Lett., Vol. 85, No. 23, (2004)
13
IR Absorbing Dyes
Anionic Dyes
Cationic Dyes
(readily anchor to the TiO2 surface)
(Not directly anchor to TiO2
surface)
Anionic compounds
used for cationic
Dyes
IR 783
IR 792
C38H46ClN2NaO6S2
C42H49ClN2O4S
Mercurochrome (MC)
2-[2-[3-[(1,3-Dihydro-3,3-dimethyl1-propyl-2H-indol-2ylidene)ethylidene]-2-(phenylthio)1-cyclohexen-1-yl]ethenyl]-3,3dimethyl-1-propylindolium
perchlorate
C20H8Br2HgNa2O6
2-[2-[2-Chloro-3-[2-[1,3-dihydro3,3-dimethyl-1-(4-sulfobutyl)-2Hindol-2-ylidene]-ethylidene]-1cyclohexen-1-yl]-ethenyl]-3,3dimethyl-1-(4-sulfobutyl)-3Hindolium hydroxide, inner salt
sodium salt
IR 820
IR 1040
C46H50ClN2NaO6S2
C40H38BCl3F4N2
2-[2-[2-Chloro-3-[[1,3-dihydro-1,1dimethyl-3-(4-sulfobutyl)-2Hbenzo[e]indol-2-ylidene]ethylidene]-1-cyclohexen-1-yl]ethenyl]-1,1-dimethyl-3-(4sulfobutyl)-1H-benzo[e]indolium
hydroxide inner salt, sodium salt
1-Butyl-2-[2-[3-[(1-butyl-6chlorobenz[cd]indol-2(1H)ylidene)ethylidene]-2-chloro-1cyclohexen-1-yl]ethenyl]-6chlorobenz[cd]indolium
tetrafluoroborate
2′,7′-Dibromo-5′-(hydroxymercurio)fluorescein
disodium salt
Bromopyrogallol Red
(BPR)
C19H10Br2O9S
5′,5′′-Dibromopyrogallolsulfonephthalein
The number indicates the peak absorption wavelength in nanometers
14
Spectral Responsivity
3
MC + IR792
Responsivity (mA/W)
BPR + IR820
IR820 + IR1040
BPR + IR1040
2
IR783
IR820
1
0
0.65
0.75
0.85
0.95
Wavelength (μm)
1.05
Peak Detectivity = (9.0 ± 0.3) ×1010 cm Hz½ W-1
Conversion Efficiency = 0.4 %
Appl. Phys. Lett., Vol. 85, No. 23, (2004)
15
Advantages and Disadvantages of DSNID
Advantages
Disadvantages
1. Low Cost
1. Slow Response
2. Fully Solid State
2. Poor long term stability
3. Detection wavelength can
be tailored using the
appropriate dye
3. Although wavelength can
be tailored, getting a
sufficiently high extinction
coefficient may not be easy.
4. Panchromatic sensitization
using several dyes
5. Readily applicable to large
area detectors
4. HOMO level should be
lower than p-type VB and
LUMO should be higher
than n-type CB
16
Colloidal Quantum Dot Detectors
17
Size Quantization Effects
CdSe/ZnS Colloidal Quantum Dots (QDs) Emission Spectra
http://www.nanopicoftheday.org/2003Pics/QDRainbow.htm
~4 nm
~15 nm
Colloidal QDs are synthesized from precursor
compounds dissolved in solutions.
18
Size Quantization Effects
(H. Q. Wang et al. Journal of Colloid and Interface Science, 316 (2007) 622-627)
TEM images of different size quantum dots (CdSe/ZnS) with emission wavelength at:
(A) 525; (B) 540; (C) 590; (D) 652; and (E) 691 nm. Average diameter: (A) 4.2 nm;
(B) 4.6 nm; (C) 6.7 nm; (D) 10.6 nm; (E) 20.1 nm. Scale bar: 20 nm.
19
PbS Colloidal QDs Bandgap vs. Particle size
Y. Wang et al. J. Chem. Phys. 87 (1987)
A. Margaret et al. Adv. Mater. 15 (2003)
Wavelength (nm)
Bulk PbS direct band gap = 0.41 eV
(λt = 3 μm)
4 nm PbS QD
(λt = 1 μm)
= 1.2 eV
20
QD Embedded Capacitor (QDEC) Type
IR Photodetectors
Optical Chopper Dielectric
Micro
Ammeter
Incoming IR
radiation
Quantum Dot
Appl. Phys. Lett., 91, 063114 2007
21
Battery
Schematics of the QDEC Type
Infrared Photodetector
PbS QD + Dielectric
medium
Glass
Top Electrical
Contact
Bottom Electrical
Contact
Glass
Glass can be replaced with IR transmitting
substrate such as Si, ZnSe, Sapphire, CaF2,
MgF2, KRS
Appl. Phys. Lett., 91, 063114 2007
22
Transparent
Conducting layer
(Fluorine-doped tin oxide)
Possible dielectric materials:
• Paraffin Wax
• Silicon Nitride
• Silicon Oxide
Responsivity (V/W)
Spectral Responsivity of the QDEC
IR Detector
300 K
200
8.7 V
20 V
30 V
40 V
150
PbS ~2 nm
100
50
0
600
800
Wavelength (nm)
Appl. Phys. Lett., 91, 063114 2007
23
1000
Summary
Advantages
Disadvantages
1. Low cost. (Fabrication does not
1. Optical chopper not practical
for some applications.
involve sophisticated epitaxial growth
techniques)
2. Density of QDs can not
increases arbitrarily. After a
threshold value it start to
conduct.
2. Can be fabricated on flexible
substrates.
3. No direct wire contact to QDs.
4. Sense only the variation of light.
Insensitive to the background.
5. Multi band capability using a
combination of QDs.
6. Spectral range can be extended
using different QD
materials
(PbSe, InSb, HgCdTe).
24
HEIWIP Free Carrier Detectors
(Heterounction Interfacial Workfunction Internal Photoemission)
25
HEIWIP Detectors
(Heterounction Interfacial Workfunction Internal Photoemission Detectors)
p+-GaAs AlxGa1-xAs
p+-GaAs AlxGa1-xAs
VB
EF
Δ
VB
Emitter
Δ
hν
h
Barrier
Biased
Zero Bias
Barrier formed by Heterojunction (p-type)
Internal workfunction Δ comes from Al fraction (x) and doping
Absorption is due to free carriers
Interface is sharp (no space charge)
APL 78, 2241 (2001)
APL 82, 139 (2003)
26
p+-GaAs
VB
EF
AlxGa1-xAs
Δd
Δx
Emitter
VB
Responsivity (a.u.)
Free Carrier Threshold of HEIWIP Detector
λt
Barrier
0
20
40
60
80 100 120 140
Wavelength (μm)
Al fraction x = 0.090
λt = Threshold Wavelength
NA = 3×1018 cm-3 Doped p+ GaAs Emitters
Δ = Δd + Δx
27
Split-off Band Detectors
28
Infrared Detector Mechanisms
E
E
Conduction
Band
Conduction
Band
Impurity
Band
E
Conduction k
Heavy Band
Light
Hole
Band
Split-off
Band
Hole
Band
E
Heavy
Hole
Band
Split-off
Band
Intersubband
levels
E
Split-off
Band
Light
Hole
Band
k Extrinsic
INTRINSIC
(InSb, HgCdTe)
Heavy
Hole
Band
k
Conduction
Band
Intersubband
levels
E
E
Conduction
Band
Impurity
Band
k
(Si:P)
Light
Hole
Band
Heavy
Hole
Band
Split-off
Band
EF
Heavy
Light
Hole
Hole
Band
Band
k
k
HH
Band
Split-off
Band
Light
Hole
Band
SO Band
LH
Band
k
HH
INTRINSIC
LH
Band
Band
(InSb, HgCdTe)
Extrinsic
(Si:P)
SO Band
QWIP
(GaAs/AlGaAs)
29
Split-Off QWIP
(GaAs/AlGaAs)
Split-off Detector Threshold Mechanisms
CB
E
p+-GaAs AlGaAs
k
L /H
Ef
HH Band
EBL/H
LH Band
EESO
SO
EBSO
SO Band
SPLIT-OFF
Intra-valence Transitions
Indirect absorption followed
by scattering and escape
Direct absorption followed
by scattering and escape
Indirect absorption followed
by escape without scattering
Threshold Energy EESO - Ef
Threshold Energy EESOf - Ef
Threshold Energy EBSO - Ef
IR Photon excites holes from the light/heavy hole bands to the split-off band (Solid Arrow)
Excited holes can scatter into the light/heavy hole bands (Dashed Arrow) and then escape,
escape
or escape directly from the split-off band
30
Appl. Phys. Lett., 89 131118 (2006)
Schematics of the Detector
RBias
Au contact
layers
Top Contact
p++ GaAs
p+ GaAs (emitter)
N
Periods
<2.5μm
AlGaAs (barrier)
Bottom Contact
p++ GaAs
Substrate
GaAs
31
Absorption and Conversion Efficiency
(Initial Sample 1332, λt = 17 μm)
0.04
Conversion Efficiency
0.02
Absorption
Split-off
0.02
0.00
2
3
4
Wavelength (m)
Split-off
0.01
Free Carrier
0.00
5
4
GaAs
Emitter
Al
Fraction
x
Δ
λt
(meV)
(μm)
Doping (cm-3)
0.15
73
17
3×1018
32
8
12
Wavelength (m)
16
Thickness (Å)
AlxGa1-xAs
Barrier
Thickness
(Å)
No of
Periods
N
188
1250
12
Different Free Carrier Threshold (λt)
Samples
Doping (cm-3)
Thickness (Å)
8
3×1018
188
600
30
207
6
3×1018
188
600
30
310
4
3×1018
188
600
30
Sample
#
Δ
λt
(meV)
(μm)
SP1
0.28
155
SP2
0.37
SP3
0.57
L /H
Band
155
meV
365
meV
365
meV
GaAs
Emitter
AlxGa1-xAs
Barrier
Thickness
(Å)
Al
Fraction
x
207
meV
365
meV
No of
Periods
310
meV
SO
Band
SP1
SP2
33
SP3
Appl. Phys. Lett., 93 021105 (2008)
Results of Different λt Samples
Δ
λt
(meV)
(μm)
SP1
155
SP2
207
Sample
#
SP3
310
Operating
Temperature
Dynamic
Resistance
@ 1V (Ω)
Dark Current
Density @ 1V
(A/cm2)
Responsivity
(mA / W)
D*
(Jones)
8
140
787 ± 1
0.663 ± 0.003
2.3 ± 0.1
(2.1 ± 0.1)×106
6
190
913 ± 1
0.875 ± 0.003
2.7 ± 0.1
(1.8 ± 0.1)×106
300
1138 ± 1
0.563 ± 0.003
0.29 ± 0.1
(6.8 ± 0.1)×105
150
(1.7±0.1) ×109
(3.4±0.1)×10-7
4
(2.1±0.1)×10-3 (2.2 ±0.1)×1010
1
Darkcurrent Density
-2
at 1V bias (A cm )
10
-1
10
SP1
SP1
SP2
SP3
Operating threshold dark current ~1 A/cm2
Design flexibility for higher D* or higher
operating temperature
-3
10
-5
10
-7
10
-9
10
20
80
140
200
260
320
Temperature (K)
34
Room Temperature Response
Responsivity (mA/W)
( SP3: 4 μm Free Carrier Threshold )
0.3
SP3
300 K
0.2
1V
2V
3V
4V
CB
k
Ef
L/H
HH
Band
0.1
LH Band
SO
0.0
2
3
4
Wavelength (m)
SO Band
SPLIT-OFF
Intra-valence Transitions
Appl. Phys. Lett., 93 021105 (2008)
35
ESO – Ef = 370 meV
3.4 μm
ESOf – Ef = 420 meV
2.9 μm
SP1 140 K
SP2 150 K
2
Responsivity (mA / W)
Responsivity (mA / W)
Responsivity Comparison for Different λt
Samples
1
0
2
3
4
Wavelength (m)
Sample
#
2
1
0
5
SP1 140 K
SP2 190 K
SP3 330 K
Free Carrier
Al Fraction
Threshold
x
(μm)
2
3
Δ
(meV)
SP1
8
0.28
155
SP2
6
0.37
207
SP3
4
0.57
310
36
4
Wavelength (m)
5
Responsivity (mA/W)
Above Room Temperature Operation
0.3
SP3
330 K
0.2
4V
Noise level
3V
2V
1V
0.1
0.0
2
3
Wavelength (m)
37
4
Different Material will Cover Different
Split-off Ranges
Material
ΔSO (meV)
λSO (μm)
InAs
GaAs
AlAs
InP
GaP
AlP
GaN
AlN
InN
410
340
300
110
80
70
20
19
3
3.2
3.6
4.1
11
16
18
62
65
410
Possibility of a room temperature dual band detector for atmospheric
windows 3-5 and 8-14 m using Arsenides & Phosphides
In1-xGaxAsyP1-y
In1-xGaxP
110 - 379
(0.11+0.421y-0.152y²)
93 - 101
0.101+0.042x-0.05x2
38
3.3 - 11
12.3 - 13.3
Summary
• High Operating Temperature (Uncooled or TE Cooled)
• Tunability (Wavelength, Detectivity, Operating
Temperature)
• Well Developed Materials, Readout Circuits, and
Integrated Circuits
• High Performance
39
GaSb Homojunction Far-IR (THz)
Detectors
40
HIWIP
(Homojunction Interfacial Workfunction Internal Photoemission Detectors)
p+-GaSb
VB
EF
p+-GaSb
Undoped
GaSb
Δ
Emitter
Δ
hν
VB
Undoped
GaSb
h
Barrier
Biased
Zero Bias
Barrier formed by Homo-junction (p-type)
Δ comes from doping
Absorption is due to free carriers
A.G.U. Perera et al., JAP (77) 915 (1995)
41
2×1018cm-3 p+ emitter
2 μm
Undoped-GaSb barrier
Δ
0.05 μm
GaSb
0.05 μm
ΔEV
5×1018cm-3 p++
p+ GaSb
0.1 μm
Top
Contact
2×1018cm-3 p+ emitter
5×1018cm-3 p++ GaSb Substrate
Appl. Phys. Lett. 90, 111109 (2007)
Grown by OMCVD
42
Bottom
Contact
Metal
contact
p+ GaSb
GaSb HIWIP Far-IR (THz) Detector
GaSb HIWIP Far-IR (THz) Response
10
Responsivity (A/W)
8
6
Frequency (THz)
10
15
7
T = 4.9 K
3.7
3.4
3.0
2.0
1.0
V
V
V
V
V
4
2
0
20
30
40
Wavelength (m)
Peak Detectivity at 36 μm = (5.7 ± 0.1)×1011 cm Hz½ W-1
Conversion Efficiency = 33 %
Appl. Phys. Lett. 90, 111109 (2007)
43
GaSb HIWIP Far-IR (THz) Response
10
15
1
Frequency (THz)
2
4
1.5
T = 4.9 K
0
Responsivity (A/W)
10
-1
3.0 V
2.0 V
1.0 V
97 μm
10
-2
10
-3
10
-4
10
20
80
140
Wavelength (m)
44
200
GaSb THz Absorption
Why GaSb ?
Wavelength (m)
5
10
4
10
3
20
40
60
80
100
-1
10
Absorption coefficient  (cm )
Absorption coefficient  cm
-1
Wavelength (m)
18
10
2
10
1
30
-3
3.4x10 cm
18
-3
1.8x10 cm
18
-3
1.2x10 cm
17
-3
5.0x10 cm
17
-3
1.6x10 cm
12
6
3
10
5
10
4
10
3
10
2
10
1
40
60
80
18
30
Frequency (THz)
20
12
6
GaAs
45
-3
3x10 cm
18
-3
5x10 cm
18
-3
8x10 cm
Frequency (THz)
GaSb
100
3
InGaSb/GaSb Heterojunctions
500
Much better for THz heterojunctions
400
Barrier is ~4 meV for 1 THz
Corresponds to 10% variation In fraction in Sb
material
< 1% Al fraction for As, N materials
Threshold wavelength
InGaSb/GaSb has a small valance band offset
300
200
100
0
0.00
0.05
0.10
x
Emitter
Barrier
Offset
GaAs
AlxGa1-xAs
530x meV
GaN
AlxGa1-xN
800x meV
InxGa1-xSb
GaSb
40x meV
46
0.15
0.20
Summary
• Higher absorption coefficient compared to GaAs
• High performance
Responsivity 9.7 A/W, Detectivity (5.7 ± 0.1)×1011 Jones at 36 μm
and 4.9 K.
• Wavelength tailorability
• Design with 14 μm threshold expected to be work at TE
cool temperatures.
• InGaSb/GaSb heterojunction has a small valance band
offset much better for THz designs
47
Future Works
48
Colloidal Quantum Dot Based UV-NIR
Dual-Band Detector
Photo Conductive
PbS QDs
ITO
ZnO
ITO
Glass Substrate
~10 μm
Responsivity
/ W)
Responsivity (kV
(kV/W)
5
16
ZnO ~ 3 nm PbS QD
4
12
0.2 V
0.5V
0.5 V
1V
1V
ZnO
3
300 K
300 K
8
2
4
1
0
200
400
600
800 1000 1200 1400
1400
Wavelength(nm)
Wavelength (nm)
In preparation to Appl. Phys. Lett.
49
Proposed dual band detector for 3-5 and 8-14 μm
atmospheric windows using Arsenides & Phosphides
TC
p++-GaAs
p+-GaAs
p++-GaAs contact
8-14 μm
Response
p++-GaAs contact
Al0.8Ga0.2As barrier
p+-In0.49Ga0.51P emitter
BC
Al0.8Ga0.2As barrier
p++-In0.49Ga0.51P contact
GaAs substrate
50
Al0.8Ga0.2As
MC
Al0.57Ga0.43As
++-InGaP emitter
p0.57
Al
Ga0.43As barrier
Al0.57Ga0.43As
p+-GaAs emitter
p++-In0.49Ga0.51P
p++-GaAs
Al0.8Ga0.2As
Al0.57Ga0.43As barrier
p+-In0.49Ga0.51P
3-5 μm
Response
List of Publications Relevant to Presented Results
1.
P. V. V. Jayaweera, S. G. Matsik, A. G. U. Perera, H. C. Liu, M. Buchanan and Z. R. Wasilewski "Uncooled
infrared detectors for 3-5 μm and beyond", Applied Physics Letters 93, 021105, (2008)
2.
P. V. V. Jayaweera, A.G.U. Perera and K. Tennakone "Why Gratzel′s cell works so well” Inorganica Chimica
Acta, 361, 707-711, (2008)
3.
A. G. U. Perera, P. V. V. Jayaweera, G. Ariyawansa, S. G. Matsik, M. Buchanan and H. C. Liu), "Room
Temperature Nano and Micro Structure Photon Detectors", Microelectronics Journal, In Press, (2008)
4.
P. V. V. Jayaweera, A. G. U. Perera, and K. Tennakone, "Displacement currents in semiconductor quantum dots
embedded dielectric media: A method for room temperature photon detection" Applied Physics Letters 91, 0631143, (2007)
5.
P. V. V. Jayaweera, S. G. Matsik, and A. G. U. Perera, Y. Paltiel, Ariel Sher and Arie Raizman, H. Luo, and H. C.
Liu, “GaSb homojunctions for Far-IR (THz) Detection” Applied Physics Letters, 90, 111109, (2007)
6.
P. V. V. Jayaweera, P.K.D.D.P. Pitigala, M.K.I. Seneviratne, A. G. U. Perera and K. Tennakone “1/f Noise in dyesensitized solar cells and NIR photon detectors” Infrared Physics & Technology, 50, 270-273 (2007)
7.
P. V. V. Jayaweera, S.G. Matsik, K. Tennakone, A.G.U. Perera, H.C. Liu and S. Krishna ) "Spin split-off transition
based IR detectors operating at high temperatures" Infrared Physics & Technology, 50, 279-283 (2007)
8.
A. G. U. Perera, S. G. Matsik, P. V. V. Jayaweera, K. Tennakone, H. C. Liu, M. Buchanan G. Von Winckel, A.
Stintz, and S. Krishna) “High Operating Temperature Split-off Band Infrared Detectors” Applied Physics Letters,
89, 131118, (2006)
9.
P. V. V. Jayaweera, P. K. D. D. P. Pitigala, A. G. U. Perera and K. Tennakone "1/f noise and dye-sensitized solar
cells", Semicond. Sci. Technol. 20, L40–L42, (2005)
10.
P. V. V. Jayaweera, A. G. U. Perera, M. K. I. Senevirathna, P. K. D. D. P. Pitigala, and K. Tennakone, “Dyesensitized near-infrared room-temperature photovoltaic photon detectors" Applied Physics Letters 85 (23), 57545756, (2004)
51
Acknowledgement
Advisor:
• Dr. Unil Perera
Department Staff:
Yvette Hilaire, Felicia Watts,
Carola Butler, Duke Windsor
Committee
• Dr. Vadym M. Apalkov
• Dr. Douglas Gies
Instrument Shop:
Charles Hopper, Peter Walker,
Dwayne Alan Torres
• Dr. Xiaochun He
• Dr. Kirthi Tennakone
Group Members
Dr. Steven Matsik, Dr. Gamini
Ariyawansa, Ranga Jayasinghe,
Dulipa Pitigala, Laura Byrum,
Jiafeng Shao, Dr. Manmohan
Singh, Greggory Rothmeier
• Dr. Brian D. Thoms
Department Chair:
• Dr. H. R. Miller
Associate Dean:
• Dr. William H. Nelson
52
Oct. 28 2008
The End
53
54
http://sales.hamamatsu.com/en/support/technical-notes.php
55
Results of Different λt Samples
Operating
Temperature
Dynamic
Resistance
@ 1V
(Ω)
Dark Current
Density @ 1V
(A/cm2)
Responsivity
(mA / W)
D*
(Jones)
8
140
787
0.663
2.3
2.1×106
6
190
913
0.875
2.7
1.8×106
300
1138
0.563
0.29
6.8×105
150
1.74×109
3.4×10-7
0.0021
2.2×1010
Δ
λt
(meV)
(μm)
SP1
155
SP2
207
Sample
#
SP3
310
4
1
Dark Current Density
-2
at 1V bias (A cm )
10
-1
10
SP1
SP2
SP3
Operating threshold dark current ~1 A/cm2
Design flexibility for higher D* or higher
operating temperature
-3
10
-5
10
-7
10
-9
10
20
80
140
200
260
320
Temperature (K)
67
PbS Colloidal QDs Absorption
A. Margaret et al. Adv. Mater. 15 (2003) 1844
Bulk PbS direct band gap = 0.41 eV
Wavelength (nm)
68
GaSb THz Absorption
Why GaSb ?
Wavelength (m)
5
10
4
10
3
20
40
60
80
100
-1
10
Absorption coefficient  (cm )
Absorption coefficient  cm
-1
Wavelength (m)
18
10
2
10
1
30
-3
3.4x10 cm
18
-3
1.8x10 cm
18
-3
1.2x10 cm
17
-3
5.0x10 cm
17
-3
1.6x10 cm
12
6
3
10
5
10
4
10
3
10
2
10
1
40
60
80
18
30
Frequency (THz)
20
12
6
GaAs
69
-3
3x10 cm
18
-3
5x10 cm
18
-3
8x10 cm
Frequency (THz)
GaSb
100
3
InGaSb/GaSb Heterojunctions
500
Much better for THz heterojunctions
400
Barrier is ~4 meV for 1 THz
Corresponds to 10% variation In fraction in Sb
material
< 1% Al fraction for As, N materials
Threshold wavelength
InGaSb/GaSb has a small valance band offset
300
200
100
0
0.00
0.05
0.10
x
Emitter
Barrier
Offset
GaAs
AlxGa1-xAs
530x meV
GaN
AlxGa1-xN
800x meV
InxGa1-xSb
GaSb
40x meV
70
0.15
0.20
Colloidal Quantum Dot based UV-NIR
Dual-band Detector
PbS QDs
ITO
ZnO
Glass Substrate
ITO
Responsivity (kV / W)
Photo Conductive
8
T=300 K
Bias =2 V
6
~3 nm PbS QD
4
2
0
200
~10 μm
ZnO
400
600
800 1000 1200 1400
Wavelength(nm)
71
Size Quantization Effects
(H. Q. Wang et al. Journal of Colloid and Interface Science, 316 (2007) 622-627)
UV–visible absorption and fluorescence spectra of different CdSe QDs synthesized by
changing the nucleation time (nucleation time from 10 to 360 s, emission from 514 to 680
nm), measured at room temperature.
72
Absorption and Conversion Efficiency
(Initial Sample HE0204, λt = 20 μm)
Quantum
Efficiency
(%)
Efficiency
Conversion
0.12
Absorption
Split-off
0.08
0.04
0.00
2
3
4
Wavelength (m)
Al
Fraction
x
Δ
λt
(meV)
(μm)
0.12
62
20
5
0.04
0.02
0.00
2
3
4
5
Wavelength (m)
GaAs
Emitter
Doping (cm-3)
Thickness (Å)
AlxGa1-xAs
Barrier
Thickness
(Å)
1×1018
188
1250
73
No of
Periods
16
Split-off Response for the 20 μm Free
Carrier Threshold Detector
E
CB
(mA / W)
Responsivity
Response (mA/W)
0.6
k
80 K
90 K
100 K
105 K
120 K
130 K
0.4
Ef
ΔL/H
HH Band
LH Band
ΔSO
SO Band
HE0204
0.2
SPLIT-OFF
Intra-valence Transitions
0.0
2
3
4
5
Wavelength (m)
Appl. Phys. Lett., 89, 131118 (2006)
74
ESO – Ef = 370 meV
3.4 μm
ESOf – Ef = 420 meV
2.9 μm
ΔSO – Ef = 420 meV
2.9 μm
Outline
•
Introduction
•
Infrared Detectors based on
1. Dye-Sensitization of Nanostructured Semiconductors
• Dye-sensitized NIR detector design, experimental results and summery
•
1/f Noise on DS nano structures
2. Displacement Currents in Semiconductor Quantum Dots (QDs)
Embedded Dielectric Media
• Size quantization effects
•
QD capacitor based detector design, experimental results and summery
3. Split-off Band Transitions in GaAs/AlGaAs Heterojunction
• High operating temperature split-off response observed from HEIWIP design for 17
μm threshold wavelength
• Uncooled split-off band detector design Experimental results and Summery
4. Free Carrier Absorption in GaSb Homojunction
• GaSb HIWIP detector design, experimental results and summery
•
Future Works
75
Advantages over other 3-5 µm Detectors
Arsenides will be used for 3 – 5 μm range
material, readout circuits, and Integrated electronics already developed
Detector
Advantage
Proposed Split-off Detector
InSb
D* =1x1011 Jones
77 K
Operating
Temperature
300 K
HgCdTe
D* =3x1010 Jones
77-240 K
~4% Bad Pixels
(256x256)
Operating
Temperature
Uniformity
300 K
~0.1% Bad Pixels (600x512)
PbSe
D* =3x1010 Jones
Threshold depends Better Stability
on Temperature
76
Threshold fixed by split-off
energy
-10
8
ln (I/T1.5)
Peak Responsivity (A/W)
10
6
4
-12
-14
2
-16
0.02
0
0
1
2
3
4
0.04
-1
1/T (K )
Bias (V)
77
0.06
Results of Different λt Samples
λt
Tmax
(μm) (K)
Δ/kTmax
Dynamic
Resistance @
1V
(Ω)
Dark Current
Density @ 1V
(A/cm2)
Responsivity
(mA / W)
D*
(Jones)
Sample
#
Δ
(meV)
SP1
155
8
140
12.8
787 ± 1
0.663 ± 0.003
2.3 ± 0.1
(2.1 ± 0.1)×106
SP2
207
6
190
12.6
913 ± 1
0.875 ± 0.003
2.7 ± 0.1
(1.8 ± 0.1)×106
SP3
310
4
300
12.0
1138 ± 1
0.563 ± 0.003
0.29 ± 0.01
(6.8 ± 0.1)×105
1
-1
10
600
SP1
SP2
SP3
Operating threshold dark current ~1 A/cm2
Maximum Operating
Temperature (K)
Dark Current Density
-2
at 1V bias (A cm )
10
-3
10
-5
10
-7
10
-9
10
20
500
Design flexibility for higher D* or higher
400 temperature
operating
300
200
100
0
80
140
200
260
Temperature (K)
Appl. Phys. Lett., 93 021105 (2008)
320
0
5
10
15
20
25
Threshold Wavelength (um)
78
30
Internal Photoemission Detectors
Type I - Nd < Nc ( ECn+ > EF )
Nd : Doping of Emitter
Nc : Mott’s Metal Insulator Transition
DEC : Band gap narrowing
Unbiased
Biased
DEc
n+
Ec
hn
Ec
D
EF
e
D = (ECn+ - EF) + DEC
A.G.U. Perera et al., JAP (77) 915 (1995)
79
i
Type II - Nc < Nd < N0 ( ECn+ < EF < ECi )
i (Barrier) i
EC
Nd : Doping density in the Emitter/Absorber
Nc : Mott’s Metal Insulator Transition
N0 : Critical concentration
hn
D
EF
D = Eci - EF
n+
EC
e

Fermi level is above the conduction band edge of the emitter

Emitter becomes semi-metallic

Infrared absorption is due to free carriers
A.G.U. Perera et al., JAP (77) 915 (1995)
80
Type III - Nd > N0 ( EF > ECi )
hn
e
Nd : Doping concentration of
the Emitter/ Absorber
E
F
N0 : Critical concentration
Bias
n ++
i (n- )
n-

Fermi level is above the conduction band edge of the barrier

Conduction band edge of the Emitter and the barrier become degenerate

Space charge region at the n++ - i interface forms the barrier

Barrier height depends on the concentration and the applied field
S. Tohyama et al., IEDM Tech. Dig. p.82 (1988)
81
p+-GaSb
CB
GaSb
GaSb
GaSb
CB
VB
EF
EF
VB
82