Applied Physics A (2023) 129:216
https://doi.org/10.1007/s00339-023-06483-7
S.I. : 50TH ANNIVERSARY OF APPLIED PHYSICS
Progress in group‑IV semiconductor nanowires based photonic
devices
Sudarshan Singh1 · Samaresh Das2 · Samit K. Ray1
Received: 18 November 2022 / Accepted: 2 February 2023 / Published online: 25 February 2023
© The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature 2023
Abstract
Despite the dominance in consumer electronics, the use of group-IV semiconductors and their heterostructures is still limited
for photonic devices, attributed to the poor emission quantum efficiency in Si and Ge due to their indirect bandgap nature.
This has posed serious bottlenecks towards the rapid progress of integrated silicon photonics. However, the recent advances
of low-dimensional Si-based heterostructures have shown enormous potential in this direction owing to the significant
modification of band structures, leading to improved optical and electronic properties over their bulk counterparts. In this
regard, one dimensional Si and Ge nanowires have witnessed an explosion of research interests because of their potential in
several promising applications for ultra-compact, silicon-compatible, and functional optoelectronic devices. Novel device
architectures integrated with single nanowires and nanowire array geometries have been actively studied and developed.
This review presents recent advances in the study of group-IV semiconductor nanowires and their heterostructure-based
photonic devices like photodetectors, solar cells and light-emitting diodes etc. Several novel but rational device designs are
presented and discussed here, from single nanowire for extraordinary performance to nanowire array heterostructures for
large area applications.
Keywords Si/Ge nanowires · Single nanowire devices · Nanowire heterostructures · Radial heterojunction · Photodetectors ·
Solar cells · Light emitting diodes
1 Introduction
There has been a progressive interest in developing new
materials and devices with reduced size and dimensionality over the last two decades for advanced electronic
and photonic applications. This has been driven by the
aggressively scaled semiconductor devices for achieving
ultra-large scale integration density (more than a billion
of transistors in a chip), high speed communication (in
GHz range) and computations with lower power dissipation. This has led to the development of an emerging area
of integrated photonics also known as “Silicon photonics”, where the optical components can be integrated on a
silicon (Si) complementary–metal–oxide–semiconductor
* Samit K. Ray
physkr@phy.iitkgp.ac.in
1
Department of Physics, Indian Institute of Technology
Kharagpur, Kharagpur 721302, India
2
Centre for Applied Research in Electronics (CARE), IIT
Delhi, Delhi 110016, India
(CMOS) platform. To achieve the goals, considerable progress has been made, particularly towards the use of Si and
germanium (Ge) nanostructures in electronic, photonic,
energy harvesting and quantum devices [1–5]. Reducing
the dimension of the material below a critical length scale
viz., exciton Bohr radius can modify the fundamental
properties such as recombination lifetime, phonon mean
free path, spin coherence length, electronic band structure
etc., compared to their bulk counterparts [6]. For instance,
quantum confinement, strain-induced band structure modification and impurity doping enabled optical emission
from Si/Ge nanostructures, which may lead to the integration of photonic components with mature Si CMOS
technology in near future [7–13]. In 1990, the report of
an intense room-temperature photoluminescence (PL)
emission from porous Si in the visible wavelength range
sparked significant research interests for using group-IV
semiconductor nanostructures for optical sources [14].
Owing to the high surface-to-volume ratio and ease of
device topology, one dimensional nanostructures such as
nanowires (NWs) or nanorods have been found to be very
13
Vol.:(0123456789)
216
Page 2 of 21
attractive for applications in photodetectors, photovoltaics, optical switches, optical interconnects, transceivers, and biological and chemical sensing etc. [15–17]. In
this regard, a combination of alloying and size variation
accompanied by the carrier confinement in one direction
in NWs results in unique transport properties of electrons,
phonons, and photons. For example, unlike pure Si or pure
Ge nanowires, SiGe alloy nanowires provide the possibility of modulating their electronic, optical, and transport
properties, not only by changing the size of the system but
also by altering the geometry of the Si/Ge interface and
the proportion of Si and Ge atoms [18]. Therefore, NWs of
group-IV materials (Si, Ge and α-Sn) and their alloys are
being widely investigated for Si optoelectronic devices, to
exploit the versatility and lower costs of Si technology to
create integrated photonic systems.
The scope of the present manuscript is to apprise recent
developments in the study of optoelectronic devices of
group-IV elemental as well as alloyed NWs and their heterostructures with other direct bandgap materials for their
potential applications in photonic devices. Indeed, one of
the key advantages of the nanowire heterostructures is the
ability to realise two different device geometries. In the first
case, the growing sections of different materials along the
wire axis form an axial heterostructure. In contrast, a radial
heterostructure is composed of two coaxial cylindrical elements: in which the core and shell are made from two different materials. In addition to NWs/nanorods [19, 20], several
geometries of one-dimensional (1D) structures such as nanocones (NCs) [21], nanodomes [22], and nanopyramids [23]
have been studied for use in nanoscale optoelectronic and
biosensing devices. Because of their excellent antireflection
properties, cone-like nanostructures are particularly promising for energy harvesting devices. On the other hand, a
higher exciton Bohr radius of Ge (~ 24.3 nm) compared to Si
(~ 4.9 nm) results in a stronger quantum confinement effect
with superior optical properties for photonic applications [9,
24–26]. Ge nanowires (Ge NWs) have therefore received a
lot of attention as promising platforms for developing optical
nanodevices such as photodetectors and light emitters that
operate in the optical communication wavelength range [17].
Fig. 1 Schematic illustration of
a an axial nanowire junction;
b a core–shell radial nanowire
junction; c a vertical nanowire
array template for growing
heterojunctions with a different
material. The regions with
different colours indicate either
different doping or different
materials for homo- and heterojunctions, respectively
13
S. Singh et al.
The recent progress in group-IV NWs-based photonic
devices, including the advances in device architecture is
reviewed in this manuscript. For single nanowire-based
devices, recently developed new strategies to improve the
performance with an extended wavelength range of operation, have been discussed. In addition to NWs homojunction, this manuscript highlights the recent developments on
several heterojunctions made-up with direct bandgap semiconductors on nanowire array templates for photodetection,
light emission, and energy harvesting applications.
2 Nanowires for photonic devices
Nanowires have been used extensively for prototype applications, such as high-efficiency solar cells [27, 28] aggressive
scaled field effect transistors (FETs), [29, 30] bio/chemical
sensors, [31, 32] low power light emitting diodes (LEDs),
[33, 34] wavelength selective photodetectors [35–37] etc.
There are a number of ways in which NWs can be used to
create 1-D photonic devices, including metal–semiconductor Schottky junctions and homo- or hetero-junction devices
which can be formed either axially along the nanowire
(Fig. 1a), or radially by the application of conformal coatings (core–shell junctions in Fig. 1b). There is also the possibility of directly growing vertical NW arrays on a variety of
substrates (Fig. 1c), which substantially broadens the scope
of device architectures and material combinations, which
can be used to realize NW photonic device arrays of large
area [38].
In addition to the advantages of the individual elements,
nanowire heterojunctions with multiple components possess
additional benefits due to combinatorial properties of different materials. Under light illumination, the built-in potential
at the junction effectively separates the electron–hole pairs
produced in the depletion region and within the diffusion
length of the axial nanowire junction in each side of Fig. 1a
[39]. The greater junction area along the surface of the
nanowires caused by the radial structure in Fig. 1b results
in a shorter carrier diffusion path for efficient carrier separation and transport. Since the dimension of both the core and
Progress in group‑IV semiconductor nanowires based photonic devices
shell can be made lower than the carriers' diffusion length
in radial junction, the bulk recombination of photogenerated
carriers is significantly reduced compared to the axial one,
giving rise to ultra-high responsivity and photoconductive
gain of the photodetector devices. In the following sections,
we will review the status and trends of recently investigated
group-IV nanowire-based photonic devices using the architectures discussed in Fig. 1.
2.1 Single nanowire photodetectors
Single nanowire-based devices are being used to create
tiny electronics with improved responsivity, low noise,
wide bandwidth, and quick response times. Due to its high
surface-to-volume ratio, nanowire devices have an inherent
photoconductive gain mechanism that allows them to sense
weak optical signals with a high sensitivity. Conventional
photodetector principles and architectures, such as semiconductor p–n or p–i–n photodiodes, are being reproduced
in NW structures in order to provide highly sensitive photodetectors with the potential for denser integration, better
specificity, and responsive to light polarisation. To realize
such devices homo- and hetero-junctions are either formed
directly during the NW growth (bottom-up approach) or
prior to the NW fabrication (top-down approach). The following provides a survey of some of the single NW and
nanowire array-based photodetectors that have been demonstrated in the literature.
2.1.1 Si nanowire devices
Due to their compatibility with CMOS processing, doping
controlled resistivity, and good thermal conductivity, silicon nanowires are among the most widely investigated onedimensional nanomaterials. However, the indirect bandgap
of Si featuring relatively poor light absorption close to the
band edge. Several approaches including leaky mode resonances [40–42], forming a metal nanoparticle/semiconductor NWs hybrid system [43, 44], engineering the size, geometry, orientation of NWs [45–49] etc. have been employed
to enhance the optical absorption in single nanowire. Single
nanowire-based detector devices are the subject of intensive research to create miniaturised devices with ultra-high
responsivity, high gain, and low noise with a large bandwidth and quick response time [35, 50, 51].
Das et al. have demonstrated a metal–semiconductor–metal (MSM) based single NW photodetector exhibiting an ultra-high responsivity over a wide wavelength range
of 400–1100 nm [52]. Si NWs of different diameters were
fabricated using metal (Ag)-assisted chemical etching of
p-type Si (100) wafers with a resistivity of ∼1.0 Ω cm. To
fabricate the device, single Si NW was connected to the
patterned electrodes (Cr/Au) on an oxidized Si substrate
Page 3 of 21 216
­(SiO2 thickness ∼300 nm) using a combination of photolithography and electron beam lithography (EBL). Figure 2a
illustrates the schematic of the fabricated single Si nanowire device. The devices fabricated with single nanowire are
capable to generate a significant photocurrent even with
zero bias. For instance, Fig. 2b depicts the typical pulsed
photocurrent response of a single nanowire photodetector
at a wavelength of 514 nm, fabricated with a NW of diameter ~ 80 nm. The data was recorded without any applied
bias, which are repeatable for several consecutive cycles.
The observation of zero-bias photoresponse indicates that
an axial built-in electric field can efficiently separate the
electron–hole pairs that are generated in the depletion region
[53–55]. Such reversible switching behaviour under optical
modulation signifies the potential of a single Si nanowire
device for optical switching applications. The fabricated
devices is also sensitive to the angle of incidence of a linearly polarized light. It has been reported that linearly polarized light incident in the direction parallel to the nanowire
axis is most effective in optically exciting the NWs [56].
The polarization dependent photoresponse of the fabricated
devices with different NW diameter, as shown in Fig. 2c,
reveal the potential use of single nanowire based devices for
polarization sensitive optical detection applications.
Moreover, the device exhibits a wideband spectral
photoresponse (Fig. 2d) ranging from visible to the nearIR region due to electronic transitions beyond the bandedges of Si. A very high value of zero-bias peak responsivity ~ 2 × ­104 ­AW−1 at a wavelength of around ~ 900 nm
for the device with ∼80 nm diameter was reported. The
responsivity value found for such a single NW based
device is much higher than those reported for most of the
photodetectors fabricated with bulk Si and nanostructured
Si surfaces [35, 36]. At a higher external bias, the depletion region width increases which leads to a higher photocurrent and results in the improved photoresponsivity
at larger applied bias. A higher responsivity of the single
NW photodetectors is attributed to their inherent photoconductive gain. Recently, Guan et al. reported numerical simulation based on the optoelectronic coupling of
the optical and electrical responses via the finite-element
method (FEM) and proposed that the radially configured
Schottky junction based devices exhibit higher responsivity in comparison to the axial one [57]. The study
revealed that radial junction in a single-nanowire design
leads to a strong light absorption along with very efficient and fast carrier transport. As shown in Fig. 2e, the
study was performed on a single nanowire based photodetector in two different Schottky junction configurations, namely radial (Device I) and axial (Device II).
In both the devices, indium tin oxide (ITO) and silver
(Ag) electrodes were used to form Schottky and Ohmic
contacts, respectively, to avoid a back-to-back Schottky
13
216
Page 4 of 21
S. Singh et al.
Fig. 2 a Schematic representation of a fabricated single Si nanowire
device. b Optical modulation characteristics of the fabricated device
at zero bias for a fixed illumination power density. c Polarization
angle dependent photocurrent for ~ 80 nm and ~ 100 nm diameter Si
nanowires. d Spectral responsivity of single nanowire photodetector
devices fabricated with a diameter ~ 80 nm for different applied bias.
[Figures a–d, reprinted from Ref. [52] with the permission of Royal
Society of Chemistry]. e Schematics of the radial (Device I) and axial
(Device II) device configurations on single Si nanowire. Device I:
ITO and Si shells enclose the Ag core, where ITO and Ag serve as
the positive and negative electrodes, respectively. Device II: single Si
nanowire is axially connected by ITO and Ag electrodes. f Typical
I–V curves of the radial and axial nanowire PDs in the dark and under
illumination (420 nm with a power density of 1 W/m2). g Photocurrent and responsivity of Device I as a function of incident light intensity at zero bias under 420 nm light illumination. h The wavelengthdependent responsivity and specific detectivity of radial Schottky
junction device at zero bias. [Figures e–h, reprinted from Ref. [57]
with the permission of AIP Publishing]
junction, which lowers the internal potential barrier and
weakens the internal electric field and carrier separation capability [57]. As show in Fig. 2f, Device I demonstrates remarkable photoresponse with a high Ion/I off
ratio ~ ­107 at zero bias, under uniform illumination condition with λ = 420 nm and a power density P 0 = 1 W/m 2.
Such enhancement in the radial structure is attributed to
the efficient separation and transport of photogenerated
carriers across larger junction area under the influence
of a built-in electric field. Moreover, the reflection of Ag
layer and the anti-reflection property of the ITO cladding result in the enhanced absorption in radial structures.
Device I exhibits an ultrahigh responsivity up to 1­ 07 A/W
(Fig. 2g), which is four orders magnitude higher than that
of an axial device, owing to the relatively short channel length of the radial structure. Moreover, as shown in
Fig. 2h, the Device I reveals a wide photocurrent spectral
response within 250 ≤ λ ≤ 950 nm with the peak response
observed at λ = 420 nm (radial) for zero applied voltage.
Thus single nanowire photodetectors fabricated in such
configurations open up a new avenue of fabricating highly
compact, self-powered devices with high responsivity,
faster response and high specific detectivity.
2.1.2 Ge nanowire devices
13
In a photoconductive detector, the responsivity of the
device is directly proportional to the carrier mobility. In
this context, the fabrication of photodetectors using Ge
nanowire is attractive not only because of its higher mobility compared to Si but also for the longer wavelength operation, extending well into the NIR region of the spectrum
due to the smaller bandgap. Single Ge NW based photodetectors have been studied to accomplish high photosensitivity [58–60]. Sett et al. reported the photoconductive
properties of vapour-liquid–solid (VLS) grown single Ge
nanowire of diameter < 100 nm in the spectral range of
300–1100 nm range [61]. The fabricated device with a
nanowire diameter of ~ 30 nm exhibits a broad band photoresponse showing peak responsivity ~ ­107 A/W at a minimal bias of 2 V with a very high photoconductive gain.
Such high gain and responsivity arise from the presence
of ­GeOx, layer at the surface of Ge nanowire, which gives
rise to a depletion layer that traps electrons of the photogenerated electron–hole pair, and leaves the hole free to
reach electrodes without recombination [61]. Our group
has also reported MSM photodetectors based on single
Progress in group‑IV semiconductor nanowires based photonic devices
Page 5 of 21 216
­G eO 2–Ge nanowire [62]. The devices show self-biased
photoresponse characteristics with a very high responsivity and polarization sensitivity. G
­ eO2–Ge nanowires were
grown by the metal catalyst assisted VLS method using
Au-coated p-Si (001) substrates in a horizontal alumina
tube furnace at 0.2 bar and 920 °C with a constant flow of
­N2 gas at a rate of 30 standard cubic centimetre per minute (sccm). The photodetection properties was studied by
fabricating a single NW based planar MSM photodetector.
For that, nanowires were coated on oxidized Si substrates
­(SiO2 thickness ∼300 nm) with pre-patterned electrodes
and an individual nanowire of a specific diameter was connected by using a combination of e-beam lithography and
focused electron beam assisted metal deposition. Typical
field-emission scanning electron microscopy (FESEM)
images of the fabricated single nanowire device at a
lower and higher magnification are presented in Fig. 3a,
b, respectively. The schematic illustration of the device
is depicted in Fig. 3c. The spectral photoresponse of the
­GeO2–Ge single nanowire MSM photodetector has been
characterized by measuring the responsivity in the spectral
range from 350 to 900 nm.
The device exhibits a peak responsivity greater than
5 × ­1 0 3 A/W with a broad spectral response cantered
on ~ 550 nm, at zero bias, as shown in Fig. 3d. A broad peak
around 550 nm arises from the large number of surface trap
states originating from the defect-induced space charge layer
in ­GeO2. The current is amplified due to the long lifetime
of trapped electrons in the single NW device. The responsivity increases sub-linearly with increasing applied bias
and nearly saturates to ∼1 × ­104 A/W above 2.0 V as the
photogenerated carriers get collected (Fig. 3d). Moreover,
a unique polarization anisotropy with parallel excitation
(TM mode) is observed in the device that generates a higher
photocurrent over that of the perpendicular excitation (TE
mode), as shown in Fig. 3e, with a polarization anisotropy
of ~ 0.62. Staudinger et al. has also reported an extraordinary
high photosensitivity of Ge based single NW photodetectors by reducing the channel lengths down to sizes at which
ballistic transport occurs, enabling the first demonstration
of an ultrahigh gain quantum Ge photodetector working in
Fig. 3 Typical FESEM image of a Ge–GeO2 core–shell single
nanowire device with a lower and b higher magnifications. c Schematic device diagram of a Ge–GeO2 core–shell single nanowire on a
­SiO2-coated Si substrate. d Room temperature bias-dependent spectral responsivity of the as-fabricated single NW device for a wavelength range of 350–900 nm. e Polarization-dependent photocurrent
of the single NW device exhibiting a cosine-function behaviour with
high anisotropy. [Figures a–e, reprinted from Ref. [62] with the permission of American Chemical Society]. f FESEM image of a single nanowire after etching step, to expose the Ge for metallization.
g Schematic illustration of a single nanowire photodetector. h SEM
image of a completed single nanowire photodetector from a 45° top
angle view. i Optical measurement setup for the nanowire photodetector, with a backside excitation of the device and confocal microscopy
setup for active area alignment. j I–V plot of single nanowire photodetector in dark and under laser excitation at 1.55 µm wavelength. k
The response of the photodetector, measured via a current amplifier,
to pulsed laser excitation at 10 kHz. [Figures f–k, reprinted from Ref.
[64] with the permission of AIP Publishing]
13
216
Page 6 of 21
ballistic mode at room temperature [63]. The epitaxially
grown Ge has also been studied for single nanowire based
photodetector exhibiting very high photoconductive gain
and low dark current with the process compatible to planar
Si-CMOS technology. Otuonye et al. investigated the photoresponse characteristics of a single Ge nanowire epitaxially grown on n-type Si (111) substrate using VLS method
[64]. The nanowire growth was achieved using low pressure
chemical vapor deposition (LPCVD). To fabricate single
nanowire devices, an e-beam lithography process was used.
Figure 3f depicts the FESEM image of a single NW after
etching steps to expose the Ge for metallization step. The
bottom contact of the nanowire was taken from the n-type
Si substrate (P-doped to 1­ 015 ­cm3), forming a Ge/Si P/N
junction. The schematic representation and FESEM image
(top view angle 45) of a fabricated single nanowire photodetector is presented in Fig. 3g, h, respectively. The nanowire
device at dark exhibits a typical PN diode behaviour with
a saturation current (dark current) of ~ 1 nA at reverse bias
(Fig. 3j) with an ideality factor of 1.9 at forward bias. The
device shows a significant enhancement in the device current
under laser excitation at a wavelength of 1.55 µm with an
internal quantum efficiency and responsivity value of 2000
and 22.6 A/W, respectively. Moreover, the fabricated single
NW photodetector showed excellent response to the pulsed
laser with frequencies above 10 kHz (Fig. 3k). However, the
speed was found to be limited due to the electrical parasitic
effects, including high output resistance of the photodetector and the large parasitic capacitance of the measurement
configuration [64].
2.1.3 SiGe nanowire devices
Silicon nanowire based photodetectors operate with a cut-off
wavelength only up to ~ 1100 nm, failing to cover the C-band
communication region. On the other hand, Ge being a preferable candidate for C-band communication, has issues of
higher dark current due to its lower bandgap and requires a
CMOS compatible fabrication process for integration into Si
photonic devices. To address these issues, new strategies to
fabricate one dimensional Si/Ge hetero-nanowires superlattice or the incorporation Ge quantum dots into silicon NW
channel appear to be a promising approach to exploit the
advantage of optical absorption characteristics of both Si
and Ge, especially for CMOS compatible infrared detection
applications [65–67]. Zhao et al. explored a new self-transformation strategy to produce one dimensional self-aligned
Ge QD islands embedded in Si nanowire with a precise location control [68]. A schematic diagram and FESEM image of
the Ge QDs embedded in Si nanowire are shown in Fig. 4a,
b, respectively. One dimensional nanostructure in the study
was grown via metal droplet assisted conversion of a bilayer
of a-Si/a-Ge thin film into hetero Ge/Si island-chain NWs
13
S. Singh et al.
(hiNWs) [66, 69], in a low temperature (< 300 °C) fabrication, as shown schematically in Fig. 4c.
The narrow Si NW is in contact with the Ge QDs through
a high quality threading-dislocation-free hetero-epitaxial
interface with a width < 50 nm. The thickness of the a-Ge
bottom layer plays an important role in defining the Ge QD/
Si NW diameter ratio and the compositional contrast in the
island-chain NW. For example, as shown in Fig. 4d, e, with
the increase of the bottom a-Ge layer thickness from 1.6
to 10 nm, the Ge QD islands in the hiNWs become more
prominent, with an increased diameter ratio from 1.1 to 3.4,
accompanied with a higher Ge content (as high as 90%) in
QD islands. To study the infrared photoresponse, two parallel hiNWs grown along the guiding edges were chosen
and connected by Au/Ti electrodes via e-beam lithography
process, with a separation of 800 nm between the source and
the drain electrodes. The device shows a stable photocurrent
response under modulated 808 nm illumination at 100 Hz as
shown in Fig. 4f. Infrared photoresponse at a wavelength of
1550 nm is shown in Fig. 4g with a calculated responsivity
value of 1.5 m ­AW−1 and a photoconductive gain > ­102. A
broad photoresponse indicates that, Ge QDs incorporated in
the Si NW channel can be used for high-density and highresolution photodetection applications in Si-based optoelectronics [68]. However the photoconductive gain of such
devices could be seriously limited by the high resistance in
the as-grown Si NWs due to low doping concentration.
We have reported the fabrication and characteristics of
a novel CMOS-compatible room-temperature IR photodetector based on Ge QDs decorated single Si nanowire
transistor integrated on Si-on-insulator (SOI) platform
[70]. Ge QDs have been grown using molecular beam
epitaxy (MBE) on a SOI substrate with top Si thickness
of 150 nm. Figure 4h depicts the typical atomic force
microscopy (AFM) topography of Ge QDs grown at a
substrate temperature of 500 °C. Figure 4i, j show the
schematic representation and an exemplary top-view
FESEM image of the fabricated back-gated single Si NW
field-effect transistor (FET) decorated with Ge QDs,
respectively. The device reveals a fairly low dark current of ~ 20 pA under a gate bias of − 4 V signifying the
off-state of the transistor with an on–off current ratio
of ∼10 3 in dark condition. The NW FET exhibits superior photoresponse for a drain bias of 0.5 V (Fig. 4k),
as the dark current ∼20 pA is enhanced up to ∼200 pA
upon irradiation at a wavelength of 1550 nm with a light
intensity of ∼5 mW/cm 2. The significantly high optical
response indicates the efficient generation and separation of photogenerated electron–hole pairs inside the single NW phototransistor, which are effectively controlled
by the gate bias. In the present device structure, the IR
spectral response is attributed to the transport of photogenerated carriers from Ge QDs to the Si channel, as
Page 7 of 21 216
Progress in group‑IV semiconductor nanowires based photonic devices
Fig. 4 a Schematic diagram of a Ge QD connected by two Si NW
electrodes on both sides and corresponding, b cross-sectional FESEM
image. c Illustration of the fabrication procedure of the hetero Ge/
Si island-chain NWs (hiNWs), led by indium (In) droplets with a
stacked a-Si/a-Ge bilayer feeding. d Dark field TEM micrograph and
EDS compositional analysis of a uniform hiNW, in the top and the
lower panels, respectively, which is grown with an initial a-Ge layer
thickness of 1.6 nm. A high-resolution TEM micrograph of the edge
region marked in d is provided in its inset to the right. Scale bars in
d and its inset measure 500 nm and 5 nm, respectively. e SEM and
EDS characteristics of other hiNWs grown with 10 nm a-Ge bottom
layer. Scale bars is 200 nm. f Photocurrent response of a multi Si NW
channel photodetector under modulated 808 nm laser incidence at
a frequency of 100 Hz. g Photocurrent signal under 1550 nm laser
beam as a function of the bias voltage. [Figures a–g, reprinted from
Ref. [68] with the permission of IOP Publishing]. h Typical AFM
images of the MBE grown Ge QDs on a SOI wafer at a substrate
temperature of 500 °C. i Schematic diagram of Ge QD-decorated
single Si NW phototransistor and j an exemplary plane-view FESEM
image of the fabricated device. k Id–Vg characteristics of the Ge QDdecorated Si NW phototransistor with different illumination powers
for λ = 1550 nm. l Schematic diagram showing the photogenerated
charge carrier transfer from Ge QDs to Si NW channel. m Drain biasdependent room-temperature spectral response for a gate bias of − 4 V
in the wavelength range ∼1200–1700 nm. (n) Polar plot of photocurrent with polarization angle of Ge QDs/Si NW device recorded
at ~ 1550 nm. [Figures h–n, reprinted from Ref. [70] with the permission of IOP Publishing]
schematically shown in Fig. 4l. The device reveals a broad
spectral response at different drain bias for a constant gate
voltage of − 4 V as presented in Fig. 4m. A peak responsivity of ∼5.5 ­AW−1 is recorded for ∼1500 nm at a drain
bias of 1 V, which is extremely high for Ge-based CMOS
compatible IR detector operating at room temperature
[19–21]. The infrared photoresponse has been found to
be polarization-selective with a polarization anisotropy
of ~ 0.34 at ~ 1550 nm as extracted from the polar photocurrent plot presented in Fig. 4n. The reported fabrication process of the IR detector is reproducible, scalable
to wafer scale, and most importantly compatible with Si
CMOS technology.
2.1.4 GeSn nanowire devices
On alloying germanium (Ge) with tin (Sn), the indirect (L)
and direct (Γ) valleys in the conduction bands of Ge are
predicted to be lower, and thus, a narrower bandgap can
be achieved [71, 72]. For a sufficient high Sn content (> 10
at.%), GeSn alloys becomes a direct bandgap semiconductor which strongly enhances the band edge absorption [73].
As a result, GeSn alloy or nanowires-based photodetectors
exhibit an extended detection range beyond 2.0 μm, with
an improved responsivity compared to Ge NW counterpart
owing to the reduced and direct bandgap of GeSn. Yang
et al. demonstrated a flexible GeSn/Ge dual-NW based
13
216
Page 8 of 21
S. Singh et al.
Fig. 5 a Schematic of the GeSn/Ge dual-NWs synthesis process.
Inset: Indium layer on graphene acts as a catalyst for Ge NW growth.
The corresponding EDX mappings of Ge, Sn and GeSn overlayer are
shown in b, Scale bar: 50 nm. c EDX line scan of the blue dashed line
in GeSn overlayer in b. d Typical Ids–Vds characteristics of the GeSn/
Ge dual-NW device in the dark and under different incident light
intensities for λ = 2.0 μm. Inset shows the SEM image of the GeSn/Ge
dual-NW device with a channel length of 5 μm, Scale bar: 10 μm. e
Spectral responsivity of GeSn/Ge dual-NW and Ge NW photodetector devices under illumination wavelengths from 1.0 to 2.2 μm with a
light intensity of 2.0 μW/μm2 at Vds = 1 mV. [Figures a–e, reprinted
from Ref. [74] with the permission of American Chemical Soci-
ety]. f Typical cross-sectional FESEM image of the Ge–Ge0.92Sn0.08
core–shell NW arrays grown using a Ge-core. g APT measurements
showing the Ge core and the inner portion of the G
­ e0.92Sn0.08 shell
[reprinted from Ref. [78] with the permission of American Chemical Society]. h Schematic illustration of a fabricated Ge–Ge0.92Sn0.08
core–shell single NW photodetector. i Responsivity and photoconductive gain at the optical communication wavelength (λ = 1.55 µm) of
the fabricated single NW photodetector as a function of applied bias
with a constant illumination power of 24 pW. Error bar represents the
maximum estimated propagating error in each measurement. [Figures
h–i, reprinted from Ref. [79], with the permission of AIP Publishing]
photodetector exhibiting a photoresponse above a wavelength of ~ 2.0 μm with a low dark current [74].
The dual NW structure consisting of a GeSn layer with
Sn content ∼10% was heteroepitaxially grown on the sidewall of a Ge NW by MBE. Figure 5a depicts the two step
growth process of GeSn/Ge dual-NWs. In the first step, Ge
NWs were synthesized on a graphene substrate using the
In layer as a catalyst at 570 °C. In the second step, a GeSn
overlayer was deposited on the sidewall of the Ge NW at
210 °C, thus forming a dual-layer GeSn/Ge NW heterostructure [74]. Compared to GeSn/Ge bulk quantum wells (QWs),
the lattice mismatch-induced compressive strain can be fully
relaxed in flexible GeSn/Ge dual-NW by the elastic deformation without forming dislocations and defects. The crosssectional EDX mapping images of Ge, Sn and overlaid scanning transmission electron microscopy (STEM) image of a
single NW, given in Fig. 5b, reveal a uniform Sn distribution
in the GeSn region, indicating that there is no Sn segregation
and precipitation in the GeSn alloy. Figure 5c is an EDX line
scan along the blue dashed line in GeSn overlayer (Fig. 5b).
Figure 5d shows the typical output characteristics (Ids–Vds)
of the GeSn/Ge dual-NW photodetector under dark and illumination without any additional gate voltage. The device
is sensitive when illuminated with a laser of wavelength
2.0 μm and the photocurrent rises at higher light intensity.
The spectral responses of two photodetectors fabricated
with bare Ge and GeSn/Ge dual-NW in the wavelength range
from 1.0 to 2.2 μm are shown in Fig. 5e. The fabricated
GeSn/Ge dual-NW detector shows improved responsivity in
comparison to the bare Ge NW with an appreciable photoresponse even at a wavelength of 2.2 μm. The photoresponse
at extended wavelength is attributed to the reduced bandgap
of GeSn in the GeSn/Ge dual-NW heterostructure in comparison to bare Ge NW [74]. However, the reduced bandgap
of GeSn also leads to undesirable increment of dark current
in the GeSn/Ge dual-NW device, which can be further suppressed due to the depletion effect from the ferroelectric
polymer side gate [74]. On the other hand, Ge–Ge1−xSnx
core–shell nanowires grown via chemical vapour deposition (CVD) process at a low temperature, exhibits enhanced
strain relaxation with high crystalline quality. The core–shell
geometry prevents the development of structural defects by
introducing some strain in the Ge-core, which lowers the
leakage current in the as-fabricated devices [73, 75–77].
Moreover, the tensile misfit strain in the Ge-core may assist
in lowering the Γ- to L-conduction valley energy that can
13
Progress in group‑IV semiconductor nanowires based photonic devices
constitute a dual direct bandgap material to improve the
device performance [72]. Lu et al. has reported a Ge/GeSn
(Sn content ~ 8.0%) core–shell single NW based p-type fieldeffect phototransistor exhibiting extended photodetection in
the short-wave infrared range up to wavelength of 2.1 μm
with superior optoelectronic properties including relatively
high mobility, high ON/OFF ratio, and high responsivity
[78].
Recently, we have reported the single Ge–Ge0.92Sn0.08
core–shell NW photodetector exhibiting superior roomtemperature responsivity with a high photo-conducting gain,
attributed to the high crystalline quality of nanowire and
shorter device length [79]. The Ge–Ge0.92Sn0.08 core–shell
NWs were grown on Si (111) in a CVD reactor using germane ­(GeH4) and tin-tetrachloride ­(SnCl4) as precursor
gases. Figure 5f depicts the cross-sectional FESEM micrograph of the as grown Ge–Ge0.92Sn0.08 core–shell NWs.
The average length of the NWs was found to be 2–3 µm.
Figure 5g depicts the atom probe tomography (APT) image
revealing the Ge core and the inner portion of the GeSn shell
with a Sn content of ~ 8.0% [78]. A single Ge–Ge0.92Sn0.08
core–shell NW photodetector was fabricated on a prepatterned oxidized Si substrate ­(SiO2 thickness ~ 300 nm)
using e-beam lithography process as schematically shown
in Fig. 5h.
The responsivity of the fabricated NW photodetector is
found to be as high as ~ 70.8 A/W at 1.0 V, which is much
superior to most of the GeSn thin film-based photodetectors. The bias-dependent responsivity and photoconductive
gain of the device at a wavelength of 1.55 µm are depicted
in Fig. 5i. Such high responsivity in NW device owing to
the reduced carrier transit time under the presence of an
external electric field and smaller effective channel length
of the device [62, 80] result in a high photoconductive gain
(more than unity). These recent progress of Ge–Ge1−xSnx
Fig. 6 Responsivity of single nanowire-based photodetectors fabricated using Si, Ge, SiGe and GeSn with different device geometries.
Outer shapes of the data points correspond to the device geometries,
which are as follows: O-metal–semiconductor-metal (MSM); □-phototransistor; ∆-junctionless MOSFET and ◊-p-n/Schottky junction
Page 9 of 21 216
core–shell nanowire photodetectors highlight their potential
for use in silicon-compatible building blocks for nanoscaleintegrated infrared photonics. Figure 6 depicts the comparison of responsivity values obtained from various single
nanowire based photodetectors fabricated using Si, Ge, SiGe
and GeSn with different device geometries.
2.2 Photodetectors of nanowire arrays
Directly grown NW arrays on a variety of substrates, schematically shown in Fig. 1c, can be employed to fabricate
large area device architectures using material combinations
available for the realization of photodetectors operating in
diverse wavelength region. Moreover, such vertical oriented
one-dimensional nanostructures exhibit an excellent light
trapping properties resulting in the enhancement of photoabsorption. We have estimated the effect of nanostructure
geometry on resultant optical properties, such as reflectance
and electric field distribution [81]. Figure 7a, b presents the
optical simulation results carried out with Si nanowires and
cone-like nanostructures, in comparison to planar Si substrate. The schematic structure and refractive index profiles
across the air-to-Si, air-to-Si NW and air-to-Si NC interfaces
are shown in Fig. 7a. Because the effective refractive index
(neff) of the medium varies smoothly from the value for the
air at the top surface (where light falls) to that for Si at the
base of the wafer, the cone-like geometry exhibits the lowest reflectivity (Fig. 7b) [81]. These Si-nanocone structures,
also known as black-Si because of their ultra-low reflectivity,
are attractive for fabricating high efficiency solar cells and
photodetectors.
Due to its large surface-to-volume ratio, 1D nanowires
can make core–shell p–n junctions, which can significantly
improve device performance when compared with thin films
and bulk counterparts [81]. Recently, a lot of interest has
arisen for photodetectors that utilize vertical NW arrays with
their growth substrates to form homo- and hetero-junctions.
Following the demonstration of Si nanostructure based photodetectors by Zheng et al., extensive efforts have been made
on Si nanowire-based junction photodetectors [82].
Several radial heterojunctions fabricated by coating a
direct bandgap compound semiconductor like ZnO [83, 84],
­TiO2 [85], CuO [86, 87], ­Cu2O [88], CdS [89, 90], ­AgInSe2
[91], molybdenum oxide ­(MoO3−x) [92], etc. on Si nanowires have been investigated. We have reported Si/CdS radial
heterojunction based high efficient photodetectors fabricated
by depositing a CdS layer on large-area, vertically aligned,
p-type Si nanowires templates [89]. Figure 7c depicts the
schematic diagram of the fabricated Si/CdS nanowire based
p–n junction revealing a peak responsivity of 1.37 ­AW−1
(Fig. 7d) and a detectivity of 4.39 × ­1011 cm ­Hz1/2 ­W−1 at
an applied bias of − 1 V. The observed responsivity corresponds to an external quantum efficiency (EQE) value of
13
216
Page 10 of 21
S. Singh et al.
Fig. 7 a Schematic illustrations of planar Si, Si nanowires, and Si
nanocones and their corresponding effective refractive index profiles
across air-to-Si wafer, air-to-Si nanowire, and air-to-Si nanocone. b
Calculated reflectance spectra of planar Si, Si nanowire, and Si nanocone arrays. [Figures a, b, reprinted from Ref [81]. with permission
of American Chemical Society]. c Schematic illustration of fabricated
Si/CdS nanowire heterojunction photodetectors. d Spectral responsivity of control planar-Si, Si nanowires, and Si/CdS core/shell nanowire photodetectors. [Figures c, d, reprinted from Ref [89]. with the
permission of American Chemical Society]. e Schematic diagram of
a conformal ­MoS2/Si NW heterojunction photodetector. f Temporal
response of the photocurrent generation at zero bias voltage under
808 nm laser illumination of the above device with weak incident
light power of 10 nW, 1 nW, and 100 pW, respectively. g Rise and fall
edges to identify response speed (time intervals between 10 and 90%
of peak signal intensity). [Figures e–g, reprinted from Ref. [95] with
the permission of John Wiley and Sons]. h Simulated (pink, blue,
and red solid lines) and measured (pink and blue dotted lines) reflection spectra of planar and black Ge at the wavelength range from 1
to 2 μm. i Cross-sectional SEM image of vertical Ge nanostructures
grown on a substrate and j a top view SEM image of the fabricated
black Ge photodetector. k Responsivity of non-passivated black and
planar Ge photodetectors at 0.5 V with illumination from 1.5 to 2 μm.
The dotted line represents responsivity corresponding to different
EQEs. [Figures h–k, reprinted from Ref. [104] with the permission of
John Wiley and Sons]
243% at − 1 V. An EQE more than 100% indicates the creation of additional charge carriers in the device due to high
photoconductive gain of the device. Recently, a self-biased
photodetector realized by directly coating earth-abundant
copper zinc tin sulphide (CZTS) nanocrystals on vertically
grown quasi one-dimensional Si templates [93]. The device
shows an extraordinary photo-to-dark ration of more than
­105 with a high-speed switching comparable to the commercial available Si/Ge photodetectors. In addition, two dimensional transition metal dichalcogenides [94, 95], carbon
based materials like carbon dots [96], graphene [97] and perovskite [98] have also been employed for the fabrication of
radial heterojunction photodetectors using Si nanowire templates. For instances, ­MoS2/Si nanowire array heterojunction
has been reported with ultrafast switching and broadband
photoresponse ranging from 300 to 1600 nm [95]. Figure 7e
depicts the schematic representation of the fabricated device
strategy of coating 2D ­MoS2 layer onto Si-NW arrays for
achieving wide-band absorption. To address the issue of
interface carrier recombination due to large surface area, an
ultrathin ­Al2O3 passivation layer was introduced to passivate
the heterojunction interface and suppress the dark current.
The device fabricated with a passivation layer decreases its
dark reverse saturation current by an order of magnitude
to 0.16 μA at the same bias [95]. The device is sensitive to
very weak optical signal in the order of pW (λ = 808 nm)
and shows a significant change in the device current above
the noise level. Figure 7f depicts the transient photoresponse
13
Page 11 of 21 216
Progress in group‑IV semiconductor nanowires based photonic devices
under laser illumination of 808 nm with different incident
power of 10 nW, 1 nW, and 100 pW showing an on–off
ratio of ~ 70, ~ 10 and ~ 3, respectively. The detector works in
self-powered mode with a responsivity and detectivity value
of 0.61/0.047 A/W−1 and 1.48 × ­1012/1.09 × ­1011 Jones at a
wavelength of 808/1550 nm, respectively. In addition, the
device shows a fast switching speed with rise/decay times
of 8.4/40.9 μs (Fig. 7g), which can meet the requirements of
high frequency optical modulation applications.
In comparison to Si, relatively fewer studies have been
done so far on Ge-nanowire-array based photodetectors. We
reported the growth and photoresponse characteristics of GeCdS core–shell nanowire radial heterojunctions photodiode
[107]. To achieve the core–shell geometry, CdS nanoparticles were coated on VLS grown Ge NW templates by a
chemical bath deposition process. The fabricated core–shell
nanowire devices exhibited an enhanced photoresponse
with broad spectral bandwidth in the wavelength range of
450–1000 nm. Recently, the improved performance in Gebased photodetectors has also been realized by growing vertical spike-like or quasi-one-dimensional nanostructures on
Ge surface, also referred to as black Ge. An et al. reported
a nanostructured Ge surface showing significant reduction
in reflectance (2%) at a wavelength range from 1 to 2 μm in
comparison to that of planar Ge (≈37%), as shown in Fig. 7h
[104]. A uniform spike-like Ge nanostructures (Fig. 7i) with
optimized dimension were obtained by C
­ l2-based room-temperature standard RIE process. The device performance has
been examined by fabricating metal–semiconductor–metal
detectors, as depicted in Fig. 7j. The responsivity of nanostructured Ge surface has been found to be enhanced significantly in the NIR range of 1.5–2.0 μm (Fig. 7k) and reveal
an EQE value exceeding 160% at 1550 nm, which is attributed to the existence of internal gain in Ge nanostructures.
The key figure-of-merit like responsivity, detectivity and
response time of group-IV semiconductor nanowire based
photodetectors fabricated with different device structures are
presented in Table 1.
3 Nanowire photovoltaic devices
Photovoltaic devices will continue to be dominated by silicon in near future following the trend of industry for decades. However, to reduce the cost of the modules, it will be
necessary to find new ways of making inexpensive Si cells
while maintaining high efficiency. [108–112]. To create solar
cells that are efficient and low-cost, semiconductor nanowires are currently being investigated. Since nanowires have
a larger surface-to-volume ratio, with dimensions comparable to minority carrier diffusion lengths and improved light
trapping, they offer promising prospects for enhancing light
absorption and charge collection efficiency in solar cells.
[5, 20]. In the following section, we will discuss the work
that has been conducted on both single as well as nanowire
array based solar cells based on Si/Ge p-n junctions and their
heterostructures.
3.1 Single nanowire solar cells
Study of a single nanowire based photovoltaic device reveals
essential properties of the material, including its optical and
electronic properties, and the efficiency of charge-separation
due to the built-in electric field at the junctions [113, 114].
In 2007, Tian et al. demonstrated the fabrication of single
Si-nanowire p–i–n homojunction solar cells, as schematically shown in Fig. 8a [27]. According to the study, the
junction's quality is critical due to its large junction area
and depletion volume. The schematic illustration and corresponding SEM image of a radial Si nanowire solar cell
are shown in Fig. 8b, c, respectively. The fabricated solar
cell exhibited an open-circuit voltage (Voc) of 260 mV and
short-circuit current (Isc) of 0.503 nA, (Fig. 8d), with a fillfactor (FF) and power conversion efficiency (PCE) of 55%
and ∼ 3.4%, respectively. Later in 2012, Thomas et al. from
the same group successfully fabricated four distinct coaxial
NW device structures exhibiting improved Voc and FF values
of 500 mV and 73%, respectively with a PCE of ∼6% in the
single nanowire device architecture [115]. Figure 8e presents
the current density (J) vs. voltage (V) curves of four distinct
diode geometries, viz., p/n, p/in, p/pn and p/pin fabricated
on a single NW with electrical contacts selectively defined
to the p-type core and n-type shell under irradiation of an
air mass 1.5 (AM 1.5) global 1-sun (100 mW/cm2) illumination [115]. The highest Voc observed for p/in geometry was
0.48 V, whereas p/pin geometry exhibited maximum short
circuit current density. On the other hand, the single NW
solar cells based on axial junction has also been investigated.
For example, an axial p-type/intrinsic/n-type single crystal
Si NWs was synthesized via Au-nanoparticle catalyzed VLS
growth method, where axial modulation was achieved by
switching dopant precursor gases at different times during
the elongation of the NW [116].
Figure 8f depicts a schematic illustration of an axial
single Si NW solar cell (top) with the corresponding SEM
image of an as grown Si NW (middle). To show the delineation of p–i–n structures, a wet etching in potassium hydroxide solution was used (bottom of Fig. 8f). The differential
etching rates for p-type, intrinsic and n-type c-Si lead to the
dissimilarities in nanowire diameter after etching. The electrical transport properties of the axial p–i–n Si NW devices
with i-region lengths of 0, 2, and 4 μm were recorded. Figure 8g shows the photovoltaic properties of the axial p-i-n Si
NW diodes under 1-sun AM 1.5 G illumination. The results
show a systematic improvement in both Voc and Isc with
increasing i-segment length, where the largest increase is
13
216
Page 12 of 21
S. Singh et al.
Table 1 Performance comparison of group-IV semiconductor based photodetectors fabricated with single as well as nanowire array and bulk/
thin films
Single Si NW
Single Ge NW
Single SiGe NW
Single GeSn NW
Si/Ge NW array
Commercial Si (Newport 818-SL)
Commercial Ge (Newport 818-IR)
GeSn (Sn ~ 12.5%)
Device geometry
Responsivity ­(AW−1)
Detectivity (cm Rise/fall time
√
HzW−1)
References
MSM
Back-gated phototransistor
Junctionless MOSFET
Bipolar phototransistors
Radial Schottky junction
Core–shell heterojunction
MSM
MSM
p–n junction
MSM
Back-gated phototransistor
MSM
MSM
Back-gated FET
MSM
MSM
Si NW array / ITO
Si NW array /CdS
Si NW array /AgInSe2
Si NW array /CuO
Si NW array /Carbon dots
Si NW array /MoS2
Si NW array /perovskite
Si NW array /CIGS
Black Si/ ­MoO3−x
Black Si/MoS2
Black Si/CZTS
Black Ge/metal
Bulk
Bulk
Thin film
2.56 × ­104 @ 0.1 V
~ 0.8 @ 5 V
~ 0.18 @
410 @ 1 V
~ ­107 @ 0 V
1.3 @ 5 V
~ 2.8 × ­107 @ 2 V
~ 0.6 × ­104 @ 0 V
~ 22.6 @
107 @
5.5 @ 1 V
3.46 × ­102 @ 2 V
1.5 × ­10–3 @ 5 V
~ 2.7 @ 1 V
70.8 @ 1 V
1.2 × ­10–3 @ 1 mV
0.55 @ 3 V
1.37 @ 1 V
11.0 × ­10–3 @ 5 V
13.05 × ­10–3 @ 2 V
0.35 @ 0 V
0.61 @ 0 V
~ 0.84 @ 0.9 V
0.33 @ 0 V
55 × ­10–3 @ 0 V
0.75 @ 2 V
0.411 @ 0 V
~3 @ 2 V
~ 0.6
~1
16.1@ 4 V
~ 1.4 × ­1013
~ ­1011
[52]
[51]
[99]
[100]
[57]
[101]
[61]
[62]
[64]
[63]
[70]
[102]
[68]
[78]
[79]
[74]
[53]
[89]
[91]
[88]
[96]
[95]
[98]
[103]
[92]
[94]
[93]
[104]
[105]
[105]
[106]
observed in moving from the p–n to p–i–n structural motif.
Such dependence suggest that the intrinsic part of the NW
is the main photoactive region [116]. The increase of Jsc can
be related to the increase of the absorber thickness.
3.2 Nanowire array solar cells
Though, single NW-based devices are useful to provide a
fundamental understanding of the photovoltaic characteristics but the power generated out of these devices is very
small for practical applications. However, as an indirect semiconductor, Si exhibits weak absorption for infrared photons,
while the efficient absorption of full above-bandgap solar
spectrum requires careful photon management. Recently,
Saive et al. discussed various approaches to improve light
13
120/100 μs
300/480 μs
9.3 × ­1014
~ 2.5 × ­1010
1.5 × ­1013
~ 4 × ­1012
22 μs
1.1/3.3 s
9.33 × ­1011
291/213 μs
88/122 μs
8.4 × ­109
4.39 × ­1011
3.79 × ­109
1.48 × ­1012
3.2 × ­1011
1.6 × ­1013
6.29 × ­1012
2.08 × ­1010
2 × ­1012
~ ­1013
~ 4.4 × ­1011
1.1 × ­1010
203/209 ms
4.3/10 μs
≤ 70/70 ms
20/40 μs
8.4/40.9 μs
4/8 μs
823/356 μs
1/51.4 μs
86/7 μs
≤ 2 μs
≤ 2 μs
–
trapping in Si solar cells [117]. Vertical nano/micro texturing is the most common method to enhance the path length
in silicon by randomizing the light direction. This is due to
their potential for industrial scale use through anisotropic
alkaline etching [118] and perfect randomization can be
achieved with such textures [23]. Therefore, large-area solar
cells made up of nanowire arrays are necessary to generate power levels useful for practical applications. A device
design composed of vertically aligned arrays of radial p–n
junction Si NW solar cells was theoretically presented by
Kayes et al. [39]. Later, Peng et al. demonstrated the fabrication of radial p–n junction solar cells on Si NWs, grown
by metal-assisted-chemical-etching (MACE), using conventional phosphorous dopant diffusion [119]. The photovoltaic
cell fabricated on a single-crystal Si substrate revealed a Voc
Progress in group‑IV semiconductor nanowires based photonic devices
Page 13 of 21 216
Fig. 8 a Schematic images of the p–i–n coaxial silicon nanowire
illustrating the core/shell nanowire junction (left); the cross-sectional
diagram showing the photogenerated electrons ­(e−) and holes ­(h+) are
swept into the n-shell and p-core, respectively, by the built-in electric field (right). b Schematic diagrams of the device fabrication.
Pink, yellow, cyan and green layers correspond to the p-core, i-shell,
n-shell and PECVD-coated ­SiO2, respectively (left); Selective etching
to expose the p-core (middle); Metal contacts deposited on the p-core
and n-shell (right). c Corresponding SEM images to the schematics
of b Scale bars; 100 nm (left), 200 nm (middle) and 1.5 µm (right).
d Dark and light I–V curves recorded from a radial p–i–n Si nanowire photovoltaic device. [Figures a–d, reprinted from Ref. [27] with
the permission of Springer Nature]. e Typical J–V characteristics of
single-NW solar cells composed of four distinct diode geometries
[reprinted from Ref. [115] with the permission of National Academy
of Sciences]. f Scheme and structural characterization of axial p–i–n
Si nanowire. Schematic of an axially modulated p–i–n Si nanowire
shown in the top. Growth is mediated with Au catalyst (gold-coloured
hemisphere) in a sequence beginning with p-, i-, and ending with
n-regions. SEM image of a uniform p–i–n axial Si NW with Au catalyst (d = 250 nm) visible on the right-end (middle), SEM images of
a p–i–n axial NW after selective wet etching (bottom). The p- and
i-type Si regions have faster etching rates than the n-type region.
Scale bars; 1 μm. g Light I–V characteristics for the i-length = 0, 2,
and 4 μm devices; the illumination intensity was 100 mW/cm2, AM
1.5G. [Figures f–g reprinted from Ref. [116] with permission of
American Chemical Society]
of ∼0.55 V and FF of 65%, resulting in a PCE of 9.31%,
which is lower than compared to a planar Si cell. The presence of surface or interfacial recombination, high series
resistance, and low current collection efficiency of the frontgrid electrodes result in the poor conversion efficiency [5].
On the other hand, solar cells based on slantingly aligned
Si NWs grown via MACE technique on a Si (111) wafer,
showed a much improved power conversion efficiency of
11.37% [120]. Such enhancement can be attributed to the
combined effects of superior antireflection properties and
improved electrical contacts in slanted nanowires, compared
to those of vertical ones. These optical properties create a
possibility for using thinner layers and thus lesser material in
Si solar cells [121]. Moreover, the photovoltaic performance
can be enhanced by developing the radial heterojunction via
depositing a thin direct bandgap semiconductor material as
an absorber layer over Si nanowire/nanocones templates.
In such device geometry, the maximum absorption occurs
in the direct bandgap material throughout the length of the
nanowire. On the other hand, the photogenerated minority carriers travel the radial distance, which is less than the
diffusion length of carriers. Inspired by the superior PCE
achieved in Si nanowire array based solar cells, several studies have been reported on crystalline Si nanowires based
p–n heterojunctions by depositing polycrystalline Si, amorphous Si and/or a direct bandgap compound semiconductor
material on nanowires by various techniques [81, 122–125].
Recently, there has been lot of interests in the development
of inorganic/organic hybrid heterojunction solar cells that
use Si nanowires coated with a polymer, which are suitable for mass production. However, the major bottleneck
to achieving greater efficiency in nanowire-based hybrid
solar cells is the limited surface coverage of spin-coated
polymer films on nanowires. In this regard, the utilization
of cone-like geometry of Si nanostructure offers a conformal
surface coverage of polymer film along with an ultra-low
reflectance in comparison to NW geometry. For instance,
Fig. 9a depicts the schematic illustration of a hybrid solar
cell composed of Si nanocones (NCs) and conductive polymer poly (3, 4-ethylenedioxythiophene)—poly (styrenesulfonate) (PEDOT:PSS) [21]. The uniform heterojunction
over the nanocones (inset of Fig. 9b), with enhanced light
13
216
Page 14 of 21
S. Singh et al.
Fig. 9 a Schematic illustration of the fabrication process for a Si
nanocone/polymer solar cell. b J–V characteristics of the Si nanocone/PEDOT:PSS solar cells, under AM 1.5 illumination, with a
back-surface doping. Inset shows the cross-sectional SEM images
of nanocones/PEDOT:PSS heterojunction solar cell with Au metal
electrode of 15 nm thickness. [Figures a, b, reprinted from Ref. [21]
with the permission of American Chemical Society]. c A schematic
diagram of Si NW/PEDOT:PSS hybrid solar cell with Au mesh electrode and d J–V characteristics of the hybrid solar cells with various
front electrodes under illumination with AM 1.5 G light at 100 mW/
cm2. [Figures c, d, reprinted from Ref. [126] with the permission of
Springer Nature]. e Photo induced open circuit voltage decay profile
for solar cells fabricated on ICP-RIE and MACE grown nanostruc-
tures along with planar Si. Red line at the initial portion of decay profile represents the best linear fit to determine the initial slope for the
calculation of recombination-limited carrier lifetime. f External quantum efficiency of Si/CdS heterojunction solar cell devices fabricated
on Si nanostructure templates grown via ICP-RIE, MACE and on planar Si. [Figures e, f, reprinted from Ref. [81] with the permission of
American Chemical Society]. g CZTS nanocrystals layer-dependent
J–V characteristics of the Si nanowire solar cells under an illumination of 100 mW/cm2 and h comparison plot of solar cell parameters
as a function of CZTS nanocrystal layer numbers on Si nanowires.
[Figures g, h, reprinted from Ref. [93] with the permission of American Chemical Society]
absorption exhibit a Jsc of ~ 29.6 mA/cm2, Voc of ~ 0.55
and FF of ~ 67.7% resulting in a PCE of ~ 11.1%. The carrier recombination at the Si nanowire/polymer interface
is a crucial concern of a hybrid heterojunction solar cell
because interface defect density significantly affects the final
device efficiency. Surface passivation of Si nanostructures
by depositing an ultra-thin layer of A
­ l2O3 using atomic layer
deposition can significantly improve the device performance.
Figure 9c depicts the schematic representation of the Si NW/
PEDOT:PSS hybrid solar cell with a passivation layer of
­Al2O3 and Au mesh as a front electrode [126].
The J–V characteristics of the hybrid solar cells with Au
mesh electrodes, recorded under an irradiation of simulated
AM 1.5 G light at an intensity of 100 mW/cm2 are depicted
in Fig. 9d. For comparison, the characteristics of a similar
device with an ITO front electrode is also displayed. Results
show the Au mesh cells exhibit a significantly enhanced
Jsc in compared to the ITO cell, which is attributed to the
enhanced optical absorbance and carrier collection of the Au
mesh cells. The best photovoltaic properties were obtained
from the 200 μm pitch cell exhibiting a PCE of 13.2%,
along with Voc = 0.539 V, Jsc = 36 mA/cm2, and FF = 67.8%.
Extensive studies have also been made on Si nanowirebased, hybrid solar cells with various other polymer like
polymers like poly—(3-hexylthiophene) (P3HT) [127, 128],
PEDOT:PSS etc. [129–132]. These studies are primarily
concerned with examining the impact of nanowire length,
surface functionalization, and polymer layer thickness that
results in a PCE of 5–10%. We have fabricated the p-n heterojunction solar cells by depositing inorganic direct bandgap
n-CdS films on p-Si nanowire synthesized via chemical and
inductively coupled plasma—reactive ion etching (ICP-RIE)
method and studied the effect of nanowire morphology on
device performance [81].
The minority carrier life time of the device has been
extracted using open-circuit voltage decay profiles as shown
in Fig. 9e. The minority carrier life times for planar Si,
MACE and ICP-RIE grown Si NCs are found to be 57.2,
4.6 and 68.6 μs, respectively [81]. Si nanocones grown via
MACE technique exhibit large defect density at the rough
surface, which lead to very high surface recombination
velocity and diode ideality factor. Similarly, the surface degradation of chemically etched Si nanostructures also affects
the EQE of the solar cell device, as depicted in Fig. 9f. An
efficient carrier extraction and collection in the device fabricated with ICP-RIE grown Si NCs result in a peak EQE
of ∼65%, whereas the cell fabricated on MACE grown NCs
shows a peak value of only ∼20%. A poor EQE in MACE
13
Progress in group‑IV semiconductor nanowires based photonic devices
grown samples is attributed to the higher recombination rate
of photo generated carriers at nanowire interfacial defect
states. On the other hand, core–shell based p–n heterojunctions fabricated by direct coating of the semiconductor
nanocrystals has also been studied [96]. We have reported
the fabrication of solution processed heterojunction solar
cells for large area application using earth abundant, nontoxic p-CZTS nanocrystals directly coated on n-Si nanowires [93]. A comprehensive study on the effect of NCs layer
thickness on key parameters of the solar cell have been
reported. Figure 9g depicts the illuminated J–V characteristics of solar cells fabricated with different nanocrystals layer
numbers. The observed PCE and other key parameters such
as Voc, Jsc, and FF of the devices fabricated with different
CZTS NC layer numbers are plotted in Fig. 9h. The PCE of
the fabricated photovoltaic devices increases almost linearly
with the layer number and is found to be maximum for four
layers, which is approximately 46% higher than the device
with one layer. The performance degradation of the device
above a critical thickness (> 4 layers) of CZTS nanocrystal
layer has been observed, which could be associated with
the activation of bulk recombination in nanocrystals and
Fig. 10 a Transport characteristics of a p–n core–shell Si-NW-CdS
junction revealing a rectified I–V curve and the inset shows a SEM
image of the fabricated device. Scale bar; 2 µm. b Room-temperature
EL spectrum of the core–shell nanowire based nano LED. [Figures
a, b, reprinted from Ref. [34] with the permission of John Wiley and
Sons]. c Fabricated well-separated radial heterojunction arrays by
depositing ZnS and AZO on KOH-treated Si nanowires. d Cross-sectional image of a single device showing the Si core and ZnS shell. e
Bottom part of the radial heterojunction showing ∼ 50 nm AZO and
Page 15 of 21 216
increased series resistance [96, 127] for the undoped CZTS
layer, resulting in a decreased short circuit current density.
4 Nanowire light emitting diodes
Being an indirect bandgap semiconductor, the implementation of Si-and Ge-based devices as light sources is hampered
because of their poor light emission efficiencies. Ge and Si
nanowires have emerged as potential building blocks having unique 1D geometry that can improve the emission efficiency owing to the quantum confinement effect. Both single
nanowire and nanowire array based light emitting diodes
have been studied by forming heterostructures with a direct
bandgap compound semiconductor. The first work on Sinanowire-based light emitting diode (LED) was reported
by Hayden et al. in 2005 [34]. They demonstrated a core/
shell p-Si/n-CdS single nanowire heterojunction fabricated
by depositing polycrystalline CdS layer of thickness ∼60 nm
on VLS grown Si NWs of ∼80 nm diameter via pulsed laser
deposition (PLD).
∼ 400 nm ZnS films. f EL spectra of the Si NW/ZnS heterojunction
at different temperatures from 10 to 400 K under a forward bias of
10 V. [Figures c–f, reprinted from Ref. [136] with the permission
of American Chemical Society]. g Schematic diagram illustrating
coaxial AZO/n-CdS/p + -black Si conical-heterojunction-based LED.
h The chromaticity diagram plotted in the CIE 1931 (x, y) for the
n-CdS/p + -black Si conical-heterojunction. [Figures g, h, reprinted
from Ref. [137] with permission of American Chemical Society]
13
216
Page 16 of 21
Figure 10a shows the transport properties of the fabricated core–shell junction showing the rectifying behaviour
of p–n diode, with the p-Si core acting as an anode. The
fabricated heterojunction exhibited room temperature electroluminescence (EL) centred at ~ 528 nm with a full-widthat-half-maximum of 20 nm under a 4 V forward bias as
shown in Fig. 10b. The observed emission originated from
the recombination of injected carriers in the polycrystalline
CdS film without any contribution from Si [34]. However,
the quantum yield of device has been found to be very low
(only ∼0.01%) necessitating further engineering of heterostructures to achieve improved properties. Thereafter, wide
research has been directed towards nanowire-array-based
LEDs [133–135]. Hsieh et al. reported electroluminescence
from ZnO/Si heterojunction nano-tips array, by combining
reactive ion etched Si nano-tips and pulsed laser deposited
ZnO [133]. We have reported the electroluminescence by
fabricating p-Si nanowire/n-ZnS core–shell type radial heterojunction nano-architecture arrays over a large area using
PLD-deposited ZnS on metal-assisted chemical etched Si
NWs [136]. Under a low forward bias condition of 2 V,
electrically driven white light emission from radial heterojunction arrays utilising an aluminium doped ZnO (AZO)
electrode has been accomplished. Figure 10c–e depict a
typical cross-sectional FESEM micrograph of the fabricated
well-separated radial heterojunction arrays showing conformal coverage of n-ZnS on Si nanowires with a thin layer of
AZO. The thickness of AZO and ZnS films were found to
be ∼50 nm and ∼400 nm, respectively. The fabricated Si
NWs/ZnS radial heterojunction arrays exhibit a broadband
emission attributed to the radiative transition in both ZnS
and the porous surface of the Si nanowire core [134, 135].
The devices have been tested in the temperature ranges from
10 to 400 K as show in Fig. 10f. It is worth noting that fabricated heterojunction exhibits a significant and stable emission even at 400 K revealing that as-fabricated Si NWs/ZnS
heterojunction arrays may function effectively at a high temperature. We have reported the black–Si based light emitting
diodes with an enhanced light extraction capability due to
nanocone geometry [137]. As a proof of concept, n-CdS/p+black Si conical-heterojunction arrays has been fabricated by
depositing n-CdS films on vertically standing Si NCs using
PLD process. The fabricated device exhibits a broadband
optical emission covering a wavelength range from 450 to
860 nm on applying a forward bias as low as 5 V. The results
are presented in Fig. 10g, h. The black dot in Fig. 10h with
coordinates (0.35, 0.41) plotted in the CIE 1931 (x, y) chromaticity diagram reveal the white light emission from the
n-CdS/p+-black Si conical-heterojunction arrays.
On the other hand, owing to the phonon-assisted indirect
and direct bandgap of 0.67 eV and ∼0.8 eV, respectively,
Ge NWs based heterojunction devices have the ability to
emit light at a wavelength of 1.54 μm, which is close to the
13
S. Singh et al.
wavelength of optical communication. Ge nanowire-based
light emitters have received much less attention than Si to
date. Recently, Fadaly et al. demonstrated an efficient light
emission from direct-bandgap hexagonal Ge and SiGe alloys
[138]. In this study, hexagonal Ge and ­Si1−xGex alloys were
grown on wurtzite GaAs nanowire templates, showing a
widely tuneable emission wavelength with a high emission
yield comparable to those of direct-bandgap III–V semiconductors. This novel approach of direct-bandgap hexagonal
­Si1−xGex opens a pathway towards the monolithic integration
of ­Si1−xGex light sources with passive Si photonics circuitry
on the same chip. We have demonstrated electrically driven
direct bandgap emission from a metal–insulator–semiconductor (MIS) structure fabricated using VLS-grown
Ge nanowires [139]. The schematic representation of the
fabricated p-Si/SiO2/Ge NW/Al2O3/Au MIS device using
core–shell Ge–GeO2 nanowires is shown in Fig. 11a. The
emission has been observed from Ge nanowire MIS LED
only under the accumulation biasing of the device (Fig. 11b)
with an onset voltage of around 10 V (current density ~ 3.7
A/cm2), which corresponds to an estimated electric field of
around 1 MV/cm1 for the fabricated device geometry. Such
a high field lead to the Fowler–Nordheim tunnelling and the
energetic injected electrons create electron–hole pairs within
the Ge nanowires by impact ionization. The light emission
characteristics as a function of operating temperature have
been investigated and presented in Fig. 11c.
The results reveal a direct gap emission, Γ-valley to
valence band (V.B.) transition, with the intensity being
maximum at ~ 1500 nm for a sample temperature ~ 10 K. A
negligible contribution from the indirect (L-valley to V.B.)
transition is detected at low temperature. With increasing
temperature, EL spectra is found to be red shifted with
decreased peak intensity for direct transition. Increasing
temperature, however, triggers emission at longer wavelengths, which gradually intensifies with the increase in
temperature. [139].
This can be explained by the dominance of phononactivated and defect-induced recombination at higher temperatures, while direct bandgap-related emission is only
prominent at lower temperatures. [139]. The observed
electroluminescence from Ge-GeO2 core–shell nanowires
in optical communication wavelength range shows the possibility to accomplish Ge-based light emitters working at
room temperature. Greil et al. demonstrated room temperature direct bandgap electroluminescence from a single Ge
nanowire by fabricating an axial p–n junction nanowire
device [140]. An axial p–n junction NWs was achieved by
VLS growth mechanism with Au colloids catalyzing particles [141]. To fabricate the devices, the p–n junction NWs
were removed from the growth substrate and deposited via
mechanical transfer on a highly doped substrate covered by
silicon oxide. Electrical contacts to individual NWs were
Progress in group‑IV semiconductor nanowires based photonic devices
Page 17 of 21 216
Fig. 11 a Schematic diagram of the p-Si/SiO2/Ge NW/Al2O3/Au MIS
LED device and b energy band diagram of the device at an accumulation (forward biased) condition showing the electron injection into
Ge from the Au electrode. c Temperature dependent electroluminescence spectra at an injected current density of ~ 5.7 A/cm2 through the
above MIS LED device. [Figures a–c, reprinted from Ref. [139] with
the permission of IOP Publishing]. d Typical SEM images of a Ge
p–n NW junction device, together with a sketch of the p- and n-type
regions of the device and the schematic equivalent circuits before and
after etching of the parasitic n-doped Ge layer. e Room temperature
EL spectra of the Ge NW p-n diode biased in the forward direction
with increasing current density. [Figures d, e, reprinted from Ref.
[140] with the permission of AIP Publishing]. f Dark-field HAADF
image and EDX mapping for Ge and Sn in a G
­ e1−xSnx nanowire with
9.4 at. % of Sn. g Photoluminescence spectra of G
­ e1−xSnx nanowires
(x = 0.06 and 0.092) recorded at 7 K. [Figures f–g, reprinted from
Ref. [75] with the permission of Springer Nature]
established by electron beam lithography, Ni/Au sputter deposition, and lift-off techniques. Figure 11d shows the SEM
image of the single NW Ge based light emitting diode. The
room-temperature EL spectra from the axial p–n junction Ge
nanowire device obtained under forward bias as a function
of injected current density are presented in Fig. 11e. The
device exhibits direct bandgap emission with EL peak centred near ~ 0.8 eV. This study demonstrated the potential of
nanowire based light source for on-chip group-IV photonics
applications at the nanoscale.
Furthermore, germanium-tin alloy nanowires are promising as silicon-compatible optical sources [142, 143]. They
have the capability of achieving a direct bandgap transition, which is critical for light emission in the shortwave
infrared (SWIR) range (0.9–2.5 μm) for a variety of photonics applications, including communication and sensing.
[71, 142–149]. A GeSn alloy-based Si photonics device
would help to resolve the “capacity crunch” currently faced
by current telecommunication technologies in the C-band
(1530–1565 nm) and L-band (1565–1625 nm) [143]. However, the indirect-to-direct bandgap crossover of unstrained
GeSn alloy occurs at a Sn content in the range of ~ 6.5 to 11
at.%, [71, 150, 151], which is much higher compared to the
equilibrium solubility of Sn in Ge (< 1.0 at.%) [150, 152].
Through a conventional bottom-up catalytic growth paradigm using noble metal and metal alloy catalysts, Biswas
et al. fabricated G
­ e1−xSnx alloy nanowires with Sn incorporation of 9.2 at.% [75]. Figure 11f depicts an energy dispersive X-ray (EDX) image and dark field high-angle annular
dark field image of G
­ e1−xSnx nanowire (Sn 9.4%) revealing
a uniform distribution of Sn in VLS nanowire growth. The
as-grown ­Ge1−xSnx nanowire exhibits a direct bandgap PL
emission at a wavelength of ~ 2.2 μm (Fig. 11g) observed
at a temperature of ~ 7 K. Few more promising results have
been reported to achieve the direct bandgap PL emission in
GeSn one dimensional structures even at room temperature
[73, 77]. A core–shell nanowire geometry has been successfully grown to achieve the direct bandgap PL emission
13
216
Page 18 of 21
even at room temperature in which a GeSn shell was grown
onto a thin Ge-core in order to promote strain relaxation by
shifting the strain into a thin Ge-core that is compliant and
prevents structural defects caused by strain [72, 153]. Electrically induced optical emission in such nanostructures is,
however, yet to be demonstrated for practical applications.
5 Conclusions and outlook
One dimensional semiconductor nanostructures have been
investigated extensively as potential building blocks for nanophotonic and nanoelectronic devices. Particular attention
has been paid to Si and Ge nanowires, due to their compatibility with current Si CMOS integrated circuit technology
and their superior scalability, performance, and leakage
control. Here, in this work, we reviewed the progress of
research on group-IV semiconductor nanowires for different photonic and photovoltaic devices. Si and Ge NWs-based
axial and core–shell p–n junctions have been discussed with
their capability to fabricate in both horizontal and vertical
topologies. The results show that, compared to their bulk or
thin-film counterparts, 1D or quasi-1D nanostructures offer
several advantages, from simple photoconductive devices to
more sophisticated NW photodetector designs. The recent
developments on single nanowire-based devices, which
exhibited ultrahigh photosensitivity due to colossal internal
photoconductive gain, discrimination of light polarization,
and broad as well as narrow band spectral sensitivity by
forming Si/Ge heterostructures or alloying have been discussed. The core–shell geometry of the p–n homo- or heterojunctions enable enhanced response and faster speed of the
photonic devices. In radial heterojunction, photogenerated
carriers are transported across the depletion layer within
their diffusion length, resulting in an efficient carrier collection. Extensive studies have also been made on vertically
oriented Si nanowires. These architectures reduce the optical
losses due to enhanced light scattering and provide superior
light absorption to realize high-performance photodetectors and solar cells. The reduced material consumption and
flexibility of NW-based solar cells will undoubtedly lead to
their increased applications in near future. In recent years,
the focus has also been made to overcome the main hurdle
of the indirect bandgap nature of group-IV semiconductors
by employing nanowire geometry including hexagonal SiGe
and Ge–GeSn core–shell structures to achieve efficient optical sources. However, the emission efficiency of Si/Ge-based
optical sources at room temperature is still in its infancy
and necessitates more investigation into band modulation
by quantum confinement, alloying, strain, and dopant engineering employing nanowire platforms. Group-IV semiconductor nanowire embodies an ideal material system in
which the electronic and optoelectronic functionalities can
13
S. Singh et al.
be combined on a single chip, opening the pathway towards
integrated device concepts and information-processing technologies. We believe that a complete set of high performance
nanophotonic components based on group-IV nanowires
can be realized in near future. However, to succeed, further
theoretical and experimental investigations on the defects
and interfaces are needed by using advanced computational,
fabrication and device characterization techniques with high
resolution and efficiency.
Acknowledgements We are very grateful to Dr. K. Das, S. Manna,
A. K. Katiyar, S. Mukherjee, A. Sarkar, J. W. John, Prof. A. K. Raychaudhuri and Prof. O. Moutanabbir and his research group for their
research results which are used in this manuscript. We also would like
to acknowledge the partial financial support from Department of Science & Technology (DST)—Ministry of Electronics and Information
Technology (MeitY) supported NNetRA “SWI” Project (Grant no. IIT/
SRIC/NT/SWI/2018-19/189), Government of India.
Author contributions SKR had the idea for the article. SS performed
the literature search and data analysis. SS and SKR prepared the draft.
SD and SKR critically revised the work.
Data availability The datasets generated during and/or analysed during the current study are available from the corresponding authors on
reasonable request.
Declarations
Conflict of interest The authors declare that there is no conflict of interest.
References
1. G. Conibeer, Mater. Today 10, 42 (2007)
2. N. Daldosso, L. Pavesi, Laser Photonics Rev. 3, 508 (2009)
3. R. Rurali, Rev. Mod. Phys. 82, 427 (2010)
4. M. Amato, M. Palummo, R. Rurali, S. Ossicini, Chem. Rev. 114,
1371 (2014)
5. S.K. Ray, A.K. Katiyar, A.K. Raychaudhuri, Nanotechnology 28,
1 (2017)
6. S.K. Ray, S. Maikap, W. Banerjee, S. Das, J. Phys. D. Appl. Phys.
46, 153001 (2013)
7. A. Sarkar, R. Bar, S. Singh, R.K. Chowdhury, S. Bhattacharya,
A.K. Das, S.K. Ray, Appl. Phys. Lett. 116, 231105 (2020)
8. X. Sun, J. Liu, L.C. Kimerling, J. Michel, Appl. Phys. Lett. 95,
1 (2009)
9. S. Das, K. Das, R.K. Singha, S. Manna, A. Dhar, S.K. Ray, A.K.
Raychaudhuri, Nanoscale Res. Lett. 6, 1 (2011)
10. R.K. Singha, S. Manna, S. Das, A. Dhar, S.K. Ray, Appl. Phys.
Lett. 96, 233113 (2010)
11. S. Manna, R. Aluguri, S. Das, R. Singha, S.K. Ray, Opt. Express
21, 28219 (2013)
12. R. Aluguri, S. Das, S. Manna, R.K. Singha, S.K. Ray, Opt. Mater.
(Amst). 34, 1430 (2012)
13. S. Manna, N. Prtljaga, S. Das, N. Daldosso, S.K. Ray, L. Pavesi,
Nanotechnology 23, 0 (2012)
14. L.T. Canham, Appl. Phys. Lett. 57, 1046 (1990)
15. F. Priolo, T. Gregorkiewicz, M. Galli, T.F. Krauss, Nat. Nanotechnol. 9, 19 (2014)
Progress in group‑IV semiconductor nanowires based photonic devices
16. M. Akbari-Saatlu, M. Procek, C. Mattsson, G. Thungström, H.-E.
Nilsson, W. Xiong, B. Xu, Y. Li, H.H. Radamson, Nanomaterials
10, 2215 (2020)
17. Z. Qi, H. Sun, M. Luo, Y. Jung, D. Nam, J. Phys. Condens. Matter 30, 334004 (2018)
18. J.N. Aqua, I. Berbezier, L. Favre, T. Frisch, A. Ronda, Phys. Rep.
522, 59 (2013)
19. Y. Yu, X. Wang, Semicond. Semimetals 94, 297–368 (2016)
20. W. Chen, P.R.I. Cabarrocas, Nanotechnology 30, 194002 (2019)
21. S. Jeong, E.C. Garnett, S. Wang, Z. Yu, S. Fan, M.L. Brongersma, M.D. McGehee, Y. Cui, Nano Lett. 12, 2971 (2012)
22. J. Zhu, C.M. Hsu, Z. Yu, S. Fan, Y. Cui, Nano Lett. 10, 1979
(2010)
23. P. Campbell, M.A. Green, J. Appl. Phys. 62, 243 (1987)
24. S. Das, R.K. Singha, A. Dhar, S.K. Ray, A. Anopchenko, N.
Daldosso, L. Pavesi, J. Appl. Phys. 110, 024310 (2011)
25. A.K. Katiyar, A. Grimm, R. Bar, J. Schmidt, T. Wietler, H.J.
Osten, S.K. Ray, Nanotechnology 27, 435204 (2016)
26. S. Singh, A.K. Katiyar, A. Sarkar, P.K. Shihabudeen, A.R.
Chaudhuri, D.K. Goswami, S.K. Ray, Nanotechnology 31,
115206 (2020)
27. B. Tian, X. Zheng, T.J. Kempa, Y. Fang, N. Yu, G. Yu, J. Huang,
C.M. Lieber, Nature 449, 885 (2007)
28. L. Hu, G. Chen, A.S.M.E. Int, Mech. Eng. Congr. Expo. Proc. 8,
1285 (2007)
29. X. Duan, Y. Huang, Y. Cui, J. Wang, C.M. Lieber, Nature 409,
66 (2001)
30. Y. Cui, Z. Zhong, D. Wang, W.U. Wang, C.M. Lieber, Nano Lett.
3, 149 (2003)
31. J.H. Chua, R.E. Chee, A. Agarwal, M.W. She, G.J. Zhang, Anal.
Chem. 81, 6266 (2009)
32. F. Patolsky, G. Zheng, C.M. Lieber, Nat. Protoc. 1, 1711 (2006)
33. F. Qian, S. Gradečak, Y. Li, C.Y. Wen, C.M. Lieber, Nano Lett.
5, 2287 (2005)
34. O. Hayden, A.B. Greytak, D.C. Bell, Adv. Mater. 17, 701 (2005)
35. E. Mulazimoglu, S. Coskun, M. Gunoven, B. Butun, E. Ozbay,
R. Turan, H.E. Unalan, Appl. Phys. Lett. 103, 083114 (2013)
36. M. Ahmad, K. Rasool, M.A. Rafiq, M.M. Hasan, Appl. Phys.
Lett. 101, 223103 (2012)
37. S.J. Choi, Y.C. Lee, M.L. Seol, J.H. Ahn, S. Kim, D. Il Moon,
J.W. Han, S. Mann, J.W. Yang, Y.K. Choi, Adv. Mater. 23, 3979
(2011)
38. R. Agarwal, Small 4, 1872 (2008)
39. B.M. Kayes, H.A. Atwater, N.S. Lewis, J. Appl. Phys. 97, 114302
(2005)
40. G. Brönstrup, N. Jahr, C. Leiterer, A. Csäki, W. Fritzsche, S.
Christiansen, ACS Nano 4, 7113 (2010)
41. L. Cao, P. Fan, A.P. Vasudev, J.S. White, Z. Yu, W. Cai, J.A.
Schuller, S. Fan, M.L. Brongersma, Nano Lett. 10, 439 (2010)
42. L. Cao, J.S. White, J.S. Park, J.A. Schuller, B.M. Clemens, M.L.
Brongersma, Nat. Mater. 8, 643 (2009)
43. J.K. Hyun, L.J. Lauhon, Nano Lett. 11, 2731 (2011)
44. K.Q. Peng, X. Wang, X.L. Wu, S.T. Lee, Nano Lett. 9, 3704
(2009)
45. S. Kim, J.F. Cahoon, Acc. Chem. Res. 52, 3511 (2019)
46. C. Zhang, Z. Yang, K. Wu, X. Li, Nano Energy 27, 611 (2016)
47. W. Liu, Y. Wang, X. Guo, J. Song, X. Wang, Y. Yi, Nanomaterials 10, 1 (2020)
48. S.K. Kim, R.W. Day, J.F. Cahoon, T.J. Kempa, K.D. Song, H.G.
Park, C.M. Lieber, Nano Lett. 12, 4971 (2012)
49. S.K. Kim, K.D. Song, T.J. Kempa, R.W. Day, C.M. Lieber, H.G.
Park, ACS Nano 8, 3707 (2014)
50. S. Samanta, K. Das, A.K. Raychaudhuri, Nanoscale Res. Lett. 8,
1 (2013)
51. V. Dhyani, A. Jakhar, J. Wellington, S. Das, J. Phys. D. Appl.
Phys. 52, 425103 (2019)
Page 19 of 21 216
52. K. Das, S. Mukherjee, S. Manna, S.K. Ray, A.K. Raychaudhuri, Nanoscale 6, 11232 (2014)
53. J. Bae, H. Kim, X.M. Zhang, C.H. Dang, Y. Zhang, Y. Jin
Choi, A. Nurmikko, Z. Lin Wang, Nanotechnology 21, 095502
(2010)
54. Y. Yang, W. Guo, J. Qi, J. Zhao, Y. Zhang, Appl. Phys. Lett. 97,
98 (2010)
55. Y. Ahn, J. Dunning, J. Park, Nano Lett. 5, 1367 (2005)
56. M.H.M. Van Weert, N. Akopian, F. Kelkensberg, U. Perinetti,
M.P. Van Kouwen, J.G. Rivas, M.T. Borgström, R.E. Algra, M.A.
Verheijen, E.P.A.M. Bakkers, L.P. Kouwenhoven, V. Zwiller,
Small 5, 2134 (2009)
57. Y. Guan, G. Cao, X. Li, Appl. Phys. Lett. 118, 153904 (2021)
58. C.J. Kim, H.S. Lee, Y.J. Cho, K. Kang, M.H. Jo, Nano Lett. 10,
2043 (2010)
59. L. Cao, J.S. Park, P. Fan, B. Clemens, M.L. Brongersma, Nano
Lett. 10, 1229 (2010)
60. C. Yan, N. Singh, H. Cai, C.L. Gan, P.S. Lee, A.C.S. Appl, Mater.
Interfaces 2, 1794 (2010)
61. S. Sett, A. Ghatak, D. Sharma, G.V.P. Kumar, A.K. Raychaudhuri, J. Phys. Chem. C 122, 8564 (2018)
62. S. Mukherjee, K. Das, S. Das, S.K. Ray, ACS Photonics 5, 4170
(2018)
63. P. Staudinger, M. Sistani, J. Greil, E. Bertagnolli, A. Lugstein,
Nano Lett. 18, 5030 (2018)
64. U. Otuonye, H.W. Kim, W.D. Lu, Appl. Phys. Lett. 110, 173104
(2017)
65. H.Y. Hui, M. De La Mata, J. Arbiol, M.A. Filler, Chem. Mater.
29, 3397 (2017)
66. Y. Zhao, H. Ma, T. Dong, J. Wang, L. Yu, J. Xu, Y. Shi, K. Chen,
P. Roca I Cabarrocas, Nano Lett. 18, 6931 (2018)
67. C. Yu, Z. Huang, G. Lin, Y. Mao, H. Hong, L. Zhang, Y. Zhao,
J. Wang, W. Huang, S. Chen, C. Li, J. Phys. D. Appl. Phys. 53,
125103 (2020)
68. Y. Zhao, L. Li, S. Liu, J. Wang, J. Xu, Y. Shi, K. Chen, P. Roca
Cabarrocas, L. Yu, Nanotechnology 31, 145602 (2020)
69. L. Yu, P.J. Alet, G. Picardi, P. Roca I Cabarrocas, Phys. Rev. Lett.
102, 2 (2009)
70. J.W. John, V. Dhyani, S. Singh, A. Jakhar, A. Sarkar, S. Das, S.K.
Ray, Nanotechnology 32, 315205 (2021)
71. S. Wirths, R. Geiger, N. Von Den Driesch, G. Mussler, T. Stoica,
S. Mantl, Z. Ikonic, M. Luysberg, S. Chiussi, J.M. Hartmann, H.
Sigg, J. Faist, D. Buca, D. Grützmacher, Nat. Photonics 9, 88
(2015)
72. A.C. Meng, M.R. Braun, Y. Wang, S. Peng, W. Tan, J.Z. Lentz,
M. Xue, A. Pakzad, A.F. Marshall, J.S. Harris, W. Cai, P.C. McIntyre, Mater. Today 40, 101 (2020)
73. S. Assali, A. Dijkstra, A. Li, S. Koelling, M.A. Verheijen, L.
Gagliano, N. Von Den Driesch, D. Buca, P.M. Koenraad, J.E.M.
Haverkort, E.P.A.M. Bakkers, Nano Lett. 17, 1538 (2017)
74. Y. Yang, X. Wang, C. Wang, Y. Song, M. Zhang, Z. Xue, S.
Wang, Z. Zhu, G. Liu, P. Li, L. Dong, Y. Mei, P.K. Chu, W. Hu,
J. Wang, Z. Di, Nano Lett. 20, 3872 (2020)
75. S. Biswas, J. Doherty, D. Saladukha, Q. Ramasse, D. Majumdar,
M. Upmanyu, A. Singha, T. Ochalski, M.A. Morris, J.D. Holmes,
Nat. Commun. 7, 11405 (2016)
76. M.S. Seifner, A. Dijkstra, J. Bernardi, A. Steiger-Thirsfeld, M.
Sistani, A. Lugstein, J.E.M. Haverkort, S. Barth, ACS Nano 13,
8047 (2019)
77. A.C. Meng, C.S. Fenrich, M.R. Braun, J.P. McVittie, A.F. Marshall, J.S. Harris, P.C. McIntyre, Nano Lett. 16, 7521 (2016)
78. L. Luo, S. Assali, M.R.M. Atalla, S. Koelling, A. Attiaoui, G.
Daligou, S. Martí, J. Arbiol, O. Moutanabbir, ACS Photonics 9,
914 (2022)
79. S. Singh, S. Mukherjee, S. Mukherjee, S. Assali, L. Luo, S. Das,
O. Moutanabbir, S.K. Ray, Appl. Phys. Lett. 120, 0 (2022)
13
216
Page 20 of 21
80. C. Soci, A. Zhang, X.Y. Bao, H. Kim, Y. Lo, D. Wang, J.
Nanosci. Nanotechnol. 10, 1430 (2010)
81. A.K. Katiyar, S. Mukherjee, M. Zeeshan, S.K. Ray, A.K. Raychaudhuri, A.C.S. Appl, Mater. Interfaces 7, 23445 (2015)
82. J.P. Zheng, K.L. Jiao, W.P. Shen, W.A. Anderson, H.S. Kwok,
Appl. Phys. Lett. 61, 459 (1992)
83. H.D. Um, S.A. Moiz, K.T. Park, J.Y. Jung, S.W. Jee, C.H. Ahn,
D.C. Kim, H.K. Cho, D.W. Kim, J.H. Lee, Appl. Phys. Lett. 98,
2009 (2011)
84. H. Kang, J. Park, T. Choi, H. Jung, K.H. Lee, S. Im, H. Kim,
Appl. Phys. Lett. 100, 041117 (2012)
85. A. Mondal, K. Bhowmik, J.C. Dhar, N.K. Singh, T. Goswami, J.
Nanosci. Nanotechnol. 14, 5390 (2014)
86. G. Akgul, F.A. Akgul, E. Mulazimoglu, H.E. Unalan, R. Turan,
J. Phys. D. Appl. Phys. 47, 065106 (2014)
87. Q. Hong, Y. Cao, J. Xu, H. Lu, J. He, J.L. Sun, A.C.S. Appl,
Mater. Interfaces 6, 20887 (2014)
88. J. Xu, Y. Cao, J. Wei, J.-L. Sun, J. Xu, J. He, Mater. Res. Express
1, 015002 (2013)
89. S. Manna, S. Das, S.P. Mondal, R. Singha, S.K. Ray, J. Phys.
Chem. C 116, 7126 (2012)
90. Y. Jiang, C. Li, W. Cao, Y. Jiang, S. Shang, C. Xia, Phys. Chem.
Chem. Phys. 17, 16784 (2015)
91. M. Kulakci, T. Colakoglu, B. Ozdemir, M. Parlak, H.E. Unalan,
R. Turan, Nanotechnology 24, 375203 (2013)
92. C. Zhao, Z. Liang, M. Su, P. Liu, W. Mai, W. Xie, A.C.S. Appl,
Mater. Interfaces 7, 25981 (2015)
93. S. Singh, A. Sarkar, D.K. Goswami, S.K. Ray, A.C.S. Appl,
Energy Mater. 4, 4090 (2021)
94. A. Sarkar, S. Mukherjee, A.K. Das, S.K. Ray, Nanotechnology
30, 485202 (2019)
95. J. Mao, B. Zhang, Y. Shi, X. Wu, Y. He, D. Wu, J. Jie, C.S. Lee,
X. Zhang, Adv. Funct. Mater. 32, 1 (2022)
96. C. Xie, B. Nie, L. Zeng, F.-X. Liang, M.-Z. Wang, L. Luo, M.
Feng, Y. Yu, C.-Y. Wu, Y. Wu, S.-H. Yu, ACS Nano 8, 4015
(2014)
97. L.B. Luo, L.H. Zeng, C. Xie, Y.Q. Yu, F.X. Liang, C.Y. Wu, L.
Wang, J.G. Hu, Sci. Rep. (2014). https://​doi.​org/​10.​1038/​srep0​
3914
98. J.-Q. Liu, Y. Gao, G.-A. Wu, X.-W. Tong, C. Xie, L.-B. Luo,
L. Liang, Y.-C. Wu, A.C.S. Appl, Mater. Interfaces 10, 27850
(2018)
99. S. Das, V. Dhyani, Y.M. Georgiev, D.A. Williams, Appl. Phys.
Lett. 108, 063113 (2016)
100. S.L. Tan, X. Zhao, K. Chen, K.B. Crozier, Y. Dan, Appl. Phys.
Lett. 109, 033505 (2016)
101. Z. Sun, Z. Shao, X. Wu, T. Jiang, N. Zheng, J. Jie, Cryst. Eng.
Commun. 18, 3919 (2016)
102. G. Lin, D. Liang, C. Yu, H. Hong, Y. Mao, C. Li, S. Chen, Opt.
Express 27, 32801 (2019)
103. L. Chen, W. Tian, L. Min, F. Cao, L. Li, Adv. Opt. Mater. 7,
1900023 (2019)
104. S. An, Y. Liao, S. Shin, M. Kim, Adv. Mater. Technol. 7, 1 (2022)
105. https://​www.​Newpo​rt.​Com/p/​818-​SL-L-​FC--​DB (2022).
106. H. Tran, T. Pham, J. Margetis, Y. Zhou, W. Dou, P.C. Grant, J.M.
Grant, S. Al-Kabi, G. Sun, R.A. Soref, J. Tolle, Y.H. Zhang, W.
Du, B. Li, M. Mortazavi, S.Q. Yu, ACS Photonics 6, 2807 (2019)
107. S.P. Mondal, S.K. Ray, Appl. Phys. Lett. 94, 223119 (2009)
108. C. Battaglia, A. Cuevas, S. De Wolf, Energy Environ. Sci. 9,
1552 (2016)
109. R. Ghosh, P.K. Giri, Sci. Adv. Today 2, 25230 (2016)
110. L.C. Andreani, A. Bozzola, P. Kowalczewski, M. Liscidini, L.
Redorici, Adv. Phys. X 4, 1548305 (2019)
111. M.A. Green, E.D. Dunlop, J. Hohl-Ebinger, M. Yoshita, N. Kopidakis, K. Bothe, D. Hinken, M. Rauer, X. Hao, Prog. Photovoltaics Res. Appl. 30, 687 (2022)
13
S. Singh et al.
112. S. Singh, A.K. Katiyar, A. Midya, A. Ghorai, S.K. Ray, Nanotechnology 28, 435704 (2017)
113. M.D. Kelzenberg, D.B. Turner-Evans, B.M. Kayes, M.A. Filier,
M.C. Putnam, N.S. Lewis, H.A. Atwater, Nano Lett. 8, 710
(2008)
114. J.H. Yun, Y.C. Park, J. Kim, H.J. Lee, W.A. Anderson, J. Park,
Nanoscale Res. Lett. 6, 1 (2011)
115. T.J. Kempa, J.F. Cahoon, S.K. Kim, R.W. Day, D.C. Bell, H.G.
Park, C.M. Lieber, Proc. Natl. Acad. Sci. U. S. A. 109, 1407
(2012)
116. T.J. Kempa, B. Tian, D.R. Kim, H. Jinsong, Z. Xiaolin, C.M.
Lieber, Nano Lett. 8, 3456 (2008)
117. R. Saive, Prog. Photovoltaics Res. Appl. 29, 1125 (2021)
118. K.E. Bean, IEEE Trans. Electron Devices 25, 1185 (1978)
119. K. Peng, Y. Xu, Y. Wu, Y. Yan, S.T. Lee, J. Zhu, Small 1, 1062
(2005)
120. H. Fang, X. Li, S. Song, Y. Xu, J. Zhu, Nanotechnology 19,
225703 (2008)
121. J. He, M.A. Hossain, H. Lin, W. Wang, S.K. Karuturi, B. Hoex,
J. Ye, P. Gao, J. Bullock, Y. Wan, ACS Nano 13, 6356 (2019)
122. E. Garnett, P. Yang, Nano Lett. 10, 1082 (2010)
123. D.R. Kim, C.H. Lee, P.M. Rao, I.S. Cho, X. Zheng, Nano Lett.
11, 2704 (2011)
124. M. Gharghi, E. Fathi, B. Kante, S. Sivoththaman, X. Zhang,
Nano Lett. 12, 6278 (2012)
125. M.M. Adachi, M.P. Anantram, K.S. Karim, Sci. Rep. 3, 1546
(2013)
126. K.T. Park, H.J. Kim, M.J. Park, J.H. Jeong, J. Lee, D.G. Choi,
J.H. Lee, J.H. Choi, Sci. Rep. 5, 1 (2015)
127. F. Zhang, B. Sun, T. Song, X. Zhu, S. Lee, Chem. Mater. 23,
2084 (2011)
128. S.-H. Tsai, H.-C. Chang, H.-H. Wang, S.-Y. Chen, C.-A. Lin,
S.-A. Chen, Y.-L. Chueh, J.-H. He, ACS Nano 5, 9501 (2011)
129. S.C. Shiu, J.J. Chao, S.C. Hung, C.L. Yeh, C.F. Lin, Chem.
Mater. 22, 3108 (2010)
130. B. Ozdemir, M. Kulakci, R. Turan, H. EmrahUnalan, Appl.
Phys. Lett. 99, 3 (2011)
131. W. Lu, C. Wang, W. Yue, L. Chen, Nanoscale 3, 3631 (2011)
132. X. Gong, Y. Jiang, M. Li, H. Liu, H. Ma, RSC Adv. 5, 10310
(2015)
133. Y.P. Hsieh, H.Y. Chen, M.Z. Lin, S.C. Shiu, M. Hofmann, M.Y.
Chern, X. Jia, Y.J. Yang, H.J. Chang, H.M. Huang, S.C. Tseng,
L.C. Chen, K.H. Chen, C.F. Lin, C. Te Liang, Y.F. Chen, Nano
Lett. 9, 1839 (2009)
134. Y.F. Chan, W. Su, C.X. Zhang, Z.L. Wu, Y. Tang, X.Q. Sun,
H.J. Xu, Opt. Express 20, 24280 (2012)
135. A. Irrera, P. Artoni, F. Iacona, E.F. Pecora, G. Franzò, M. Galli,
B. Fazio, S. Boninelli, F. Priolo, Nanotechnology 23, 075204
(2012)
136. A.K. Katiyar, A.K. Sinha, S. Manna, S.K. Ray, A.C.S. Appl,
Mater. Interfaces 6, 15007 (2014)
137. A. Sarkar, A.K. Katiyar, S. Mukherjee, S. Singh, S.K. Singh,
A.K. Das, S.K. Ray, A.C.S. Appl, Electron. Mater. 1, 25 (2019)
138. E.M.T. Fadaly, A. Dijkstra, J.R. Suckert, D. Ziss, M.A.J.
van Tilburg, C. Mao, Y. Ren, V.T. van Lange, K. Korzun, S.
Kölling, M.A. Verheijen, D. Busse, C. Rödl, J. Furthmüller,
F. Bechstedt, J. Stangl, J.J. Finley, S. Botti, J.E.M. Haverkort,
E.P.A.M. Bakkers, Nature 580, 205 (2020)
139. S. Manna, A. Katiyar, R. Aluguri, S.K. Ray, J. Phys. D. Appl.
Phys. 48, 215103 (2015)
140. J. Greil, E. Bertagnolli, B. Salem, T. Baron, P. Gentile, A.
Lugstein, Appl. Phys. Lett. 111, 223103 (2017)
141. R.S. Wagner, W.C. Ellis, Appl. Phys. Lett. 4, 89 (1964)
142. R. Soref, D. Buca, S.-Q. Yu, Opt. Photonics News 27, 32
(2016)
Progress in group‑IV semiconductor nanowires based photonic devices
143. O. Moutanabbir, S. Assali, X. Gong, E. O’Reilly, C.A. Broderick,
B. Marzban, J. Witzens, W. Du, S.Q. Yu, A. Chelnokov, D. Buca,
D. Nam, Appl. Phys. Lett. 118, 110502 (2021)
144. D. Zhang, C. Xue, B. Cheng, S. Su, Z. Liu, X. Zhang, G. Zhang,
C. Li, Q. Wang, Appl. Phys. Lett. 102, 141111 (2013)
145. S. Xu, W. Wang, Y.-C. Huang, Y. Dong, S. Masudy-Panah, H.
Wang, X. Gong, Y.-C. Yeo, Opt. Express 27, 5798 (2019)
146. S. Xu, K. Han, Y.-C. Huang, Y. Kang, S. Masudy-Panah, Y. Wu,
D. Lei, Y. Zhao, X. Gong, and Y.-C. Yeo, in 2019 Symp. VLSI
Technol. (IEEE, 2019), pp. T176–T177.
147. H. Wang, Y. Chen, J. Zhang, G. Zhang, Y. Huang, and X. Gong,
in 2021 Symp. VLSI Circuits (IEEE, 2021), pp. 1–2.
148. S. Mahato, A. Ghorai, S.K. Srivastava, M. Modak, S. Singh, S.K.
Ray, Adv. Energy Mater. 10, 2001305 (2020)
149. S. Ghose, S. Singh, T.S. Bhattacharya, A.C.S. Appl, Mater. Interfaces 12, 7727 (2020)
150. S. Gupta, B. Magyari-Köpe, Y. Nishi, K.C. Saraswat, J. Appl.
Phys. 113, 073707 (2013)
Page 21 of 21 216
151. T.R. Harris, M.-Y. Ryu, Y.K. Yeo, B. Wang, C.L. Senaratne, J.
Kouvetakis, J. Appl. Phys. 120, 085706 (2016)
152. S. Wirths, D. Buca, S. Mantl, Prog. Cryst. Growth Charact.
Mater. 62, 1 (2016)
153. S. Assali, M. Albani, R. Bergamaschini, M.A. Verheijen, A. Li,
S. Kölling, L. Gagliano, E.P.A.M. Bakkers, L. Miglio, Appl.
Phys. Lett. 115, 113102 (2019)
Publisher's Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional affiliations.
Springer Nature or its licensor (e.g. a society or other partner) holds
exclusive rights to this article under a publishing agreement with the
author(s) or other rightsholder(s); author self-archiving of the accepted
manuscript version of this article is solely governed by the terms of
such publishing agreement and applicable law.
13