InAs on GaAs Photodetectors Using Thin InAlAs Graded Buffers and Their Application to Exceeding Short-Wave Infrared Imaging at 300 K

Abstract

Short-wave infrared (SWIR) detectors and emitters have a high potential value in several fields of applications, including the internet of things (IoT) and advanced driver assistance systems (ADAS), gas sensing. Indium Gallium Arsenide (InGaAs) photodetectors are widely used in the SWIR region of 1–3 μm; however, they only capture a part of the region due to a cut-off wavelength of 1.7 μm. This study presents an InAs p-i-n photodetector grown on a GaAs substrate (001) by inserting 730-nm thick InxAl1−xAs graded and AlAs buffer layers between the InAs layer and the GaAs substrate. At room temperature, the fabricated InAs photodetector operated in an infrared range of approximately 1.5–4 μm and its detectivity (D*) was 1.65 × 108 cm · Hz1/2 · W−1 at 3.3 μm. To demonstrate performance, the Sherlock Holmes mapping images were obtained using the photodetector at room temperature.

Full text

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InAs on GaAs Photodetectors Using
Thin InAlAs Graded Buers and
Their Application to Exceeding
Short-Wave Infrared Imaging at
300 K
Soo Seok Kang1,2, Dae-Myeong Geum
1, Kisung Kwak1, Ji-Hoon Kang1,
Cheol-Hwee Shim
3, HyeYoung Hyun3, Sang Hyeon Kim
1, Won Jun Choi1,
Suk-Ho Choi2, Min-Chul Park1 & Jin Dong Song
1
Short-wave infrared (SWIR) detectors and emitters have a high potential value in several elds of
applications, including the internet of things (IoT) and advanced driver assistance systems (ADAS), gas
sensing. Indium Gallium Arsenide (InGaAs) photodetectors are widely used in the SWIR region of 1–3
μm; however, they only capture a part of the region due to a cut-o wavelength of 1.7 μm. This study
presents an InAs p-i-n photodetector grown on a GaAs substrate (001) by inserting 730-nm thick
InxAl1−xAs graded and AlAs buer layers between the InAs layer and the GaAs substrate. At room
temperature, the fabricated InAs photodetector operated in an infrared range of approximately 1.5–4
μm and its detectivity (D*) was 1.65 × 108 cm · Hz1/2 · W−1 at 3.3 μm. To demonstrate performance, the
Sherlock Holmes mapping images were obtained using the photodetector at room temperature.
Indium Gallium Arsenide (InGaAs) photodetectors on Indium Phosphide (InP) substrates are commonly used to
detect the ‘classic’ short-wave infrared (SWIR) range of 1–1.7 μm. Such devices are widely used in spectroscopy,
night vision, gas sensing and telecommunications applications1–5.
Recently, a ‘capacity crunch’ in this wavelength range was predicted based on the explosive increase in network
trac that is being driven by the development of the internet of things (IoT). Systems such as ber optics, wave-
guides, emitters, and detectors are undergoing extensive research to nd ways to extend performance from 1.7 μm
to longer wavelengths in the SWIR range6–11. Such extensions could support a variety of applications, including
pedestrian detection for advanced driver assistance systems (ADAS), and the identication of particulate matter
in the air12.
HgCdTe (MCT) detectors are currently in widespread use in the SWIR range, but detectors are subject to
high price and require an integrated cooling system13. Also, the extended InGaAs and InGaAs/GaAsSb type-II
quantum well photodetectors have been intensively studied, but so far cannot detect the full SWIR region14–17.
Detectors that are of low-cost and fully cover the SWIR region are required.
Indium arsenide (InAs), one of the III-V materials, has a high electron mobility of 30,000 cm2/V·s and a direct
band gap of 0.417 eV. Due to the narrow band gap, InAs-based detectors can sense SWIR light that is longer than
the cut-o wavelength of a conventional InGaAs photodetector. However, although the physical properties of
InAs constitute a photodetector that is advantageous, manufacturing the detectors is dicult due to the cost of
InAs wafers, which are more expensive than InP wafers.
GaAs substrates are cheaper than InAs and InP substrates; however, the lattice mismatch between GaAs and
InAs is 7.2%, which leads to inevitable defects such as mist dislocations (MDs) and threading dislocations (TDs).
1Center for Opto-Electronic materials and devices, Korea Institute of Science and Technology, Seoul, 136-791, Republic
of Korea. 2Department of Applied Physics and Institute of Natural Sciences, Kyung Hee University, Yongin, 17104,
Republic of Korea. 3Advanced Analysis Center, Korea Institute of Science and Technology, Seoul, 136-791, Republic of
Korea. Correspondence and requests for materials should be addressed to M.-C.P. (email: minchul@kist.re.kr) or J.D.S.
(email: jdsong@kist.re.kr)
Received: 20 May 2019
Accepted: 22 August 2019
Published: xx xx xxxx
OPEN
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e dislocations have a negative impact on the physical properties of InAs due to electron-defect scattering. In
order to minimize defects caused by lattice mismatch, it is essential to employ a metamorphic growth technique.
For example, these include the low and high growth temperature (LT-HT) InxGa1−xAs step graded buer and
InxAl1−xAs step graded buer layer methods18–20.
In the LT-HT growth method, the InAs lm is grown at LT and then the InAs lm is grown at HT. e initial
high density InAs nucleation covers the GaAs substrate at LT, and the strain induced by lattice mismatch between
the GaAs and InAs relaxes by generating high density dislocations. Subsequently, the LT InAs is reconstructed
into a continuous lm by heating to HT. en, the reconstructed LT InAs lm acts as a pseudo substrate for the
growth of high-quality InAs lms18. In LT GaAs lms grown on an InP substrate, the dislocations generated by
stress-induced lattice mismatch are immobilized and the dislocations slide towards a symmetric orientation. As
the lm thickness increases, the dislocation density decreases by symmetrically oriented dislocation scattering in
two dimensions21.
In the graded buer layer method, the stress induced by lattice mismatch can be relaxed through stepwise or
linearly constant lattice change, and the dislocation density is decreased due to the hardening of the alloy for an
In composition of 0.5 for InxGa1−x(Al1−x)As20.
Recently, Loke et al.22–24 have reported an InAs photodetector grown on a GaAs substrate using the InxAl1−xAs
graded buer layer and LT-GaAs. e composition x was continuously changed from 0 to 1. e InAs layer was
the surface of the graded buer layer, and was not an insulating layer for the InAs lm. is conductive layer pre-
vented the precise electronic characterization of the InAs layer. Moreover, the motion of dislocations, which leads
to the degradation of the devices due to carrier-defect scattering, is not directly shown in this report.
In our previous work, a high-quality InSb lm was grown on a GaAs substrate using an InxAl1−xSb continuous
graded buer layer25. Unlike other reports, the growth temperature of the continuous graded buer layer grad-
ually decreased because the growth temperature of InSb is lower than that of AlSb. Proper control of the growth
temperature can minimize slippage and generation of dislocations by increasing yield strength.
In the aforementioned two references, the thickness of the continuous buer layer was above 1.4 μm. e
dislocation density is well known to be inversely proportional to lm thickness. However, a thick buer layer is
not desirable for real applications.
In this work, a high-quality InAs lm was obtained using an InxAl1−xAs graded buer layer, with x = 0 to
x = 0.87 for the insulating surface of the graded buer layer. e composition x was gradually changed by varying
the growth rate of In and Al, while gradually decreasing the growth temperature. e In0.87Al0.13As layer closest
to the InAs lm showed sucient insulating property to allow precise electronic measurement of the InAs lms,
and has proper Al composition to be used as sacricial layer for future integration. In our study, the eect of the
InxAl1−xAs graded buer layer for fabricating high-quality InAs lm is better than that of LT-HT buer layers.
To fabricate a SWIR imaging operating at room temperature, the p-i-n InAs was grown on a semi-insulating (SI)
GaAs substrate by inserting the InxAl1−xAs graded buer layer.
Results and Discussion
ree samples of InAs were grown on SI-GaAs (001) using In0.87Al0.13As - In0.87Al0.13As (LH1), InAs - In0.87Al0.13As
(LH2), and InxAl1−xAs graded (G1) buer layers in a Riber compact 21E solid source molecular beam epitaxy
(MBE) system, as shown in Fig.1a.
In the LH1 and LH2 samples, the GaAs substrate was degassed at 400 °C and then the removal of the native
oxide from the substrate was carried out in an As2 atmosphere supported by a valved-cracker As cell at the sub-
strate temperature (Ts) of 620 °C for 10 min. Subsequently, a 100-nm thick GaAs buer layer having a Ga growth
rate of 1.82 Å/s was deposited on a at surface at 580 °C. An InAs layer of 300 nm thickness was grown in a GaAs
buer layer at the LT of 270 °C and then an In0.87Al0.13As layer of 300 nm thickness was cultured at an HT of 470 °C
in the LH1. Subsequently, an InAs lm having a thickness of 500 nm was grown at 470 °C. e growth procedure
of LH2 is the same as that of LH1, but with a 300-nm thick In0.87Al0.13As layer, instead of an InAs lm grown at
LT. e In growth rate of In0.87Al0.13As and InAs was 2.62 Å/s, while the Al growth rate of the LT-HT samples was
0.4 Å/s.
During the growth procedure of the G1 samples, the degassed, deoxy, and GaAs buer layer deposition pro-
cesses were similar to those mentioned above. en, a 100 nm thick AlAs layer was deposited with an Al growth
rate of 2.7 Å/s at a Ts of 580 °C. At that point, an InxAl1−xAs graded buer layer was grown while gradually chang-
ing the growth rate of In from 0 Å/s to 2.62 Å/s, and the Al from 2.7 Å/s to 0.4 Å/s, while the Ts was gradually
decreased from 530 to 470 °C. Finally, a 500-nm InAs lm was grown at a Ts of 470 °C.
e structure of the In0.87Al0.13As terminated (GT) sample is shown in Fig.1a, and the sample demonstrated
an insulating property.
Figure1b shows the electron mobilities and surface roughness of four samples. e electron mobilities of LH1,
LH2, G1, and GT were 4,375, 4,749, 9,275 and 617 cm2/V·s, respectively. Apart from the GT sample, the other
samples showed the electron mobilities of a 500-nm thick InAs lm, and the G1 sample had the highest electron
mobility. is implies that the graded buer layer can overcome the lattice mismatch between GaAs and InAs,
and that it is a more ecient approach than the LT-HT growth method for obtaining a high quality InAs lm on
a GaAs substrate.
e surface roughness of LH1, LH2, G1, and GT was 1.1, 1.5, 2.1, and 7.2 nm, respectively, and obtained
images of 10 μm × 10 μm, as shown in Fig.1c. Although the surface roughness of G1 was higher than that of
LH1 and LH2, the electron mobility of G1 was also higher than that of LH1 and LH2. is means that surface
scattering does not have a major inuence in the degradation of carrier transport, taking into account the electron
mobilities and surface roughness.
e degradation of electron mobility ascribes to electron-defect scattering, and several hillocks and pits in
LH1 and LH2 are slightly higher than that in G1, as shown in Fig.1c. e high density of hillocks and pits has
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a negative impact on electron transport. e surface morphology of GT is the roughest among the samples,
and the pyramidal surface morphology implies that the graded buer layer could grow at low growth tempera-
ture. Interestingly, the high surface roughness of the graded buer layer reduced from 7.2 nm to 2.1 nm aer the
500 nm thick InAs grew in the GT. e electron mobility of the GT was 617 cm2/V·s, and its resistivity of 18 /
cm was also higher than the G1 resistivity of 0.015 /cm (data not shown). erefore, the electron mobility of the
500-nm thick InAs lm was precisely achieved due to the insulating property of the GT layer.
e 2θ/ω spectra of samples are shown in Fig.1d. e In0.87Al0.13As 2θ/ω peaks in LH1 and LH2 were at
61.71° and 61.94°, respectively, while the GaAs (004) peak was 66.05°. e 2θ/ω angle dierence of In0.87Al0.13As
between LH1 and LH2 is attributed to the In and Al growth rates, which was measured at high temperature. e
growth rate varied at low temperature. In particular, the In growth rate rapidly increased due to a reduction in the
re-evaporation of In at low temperature.
For G1, the peak of the InxAl1−xAs graded buer layer was widely obtained in the range of 65.5° to 61.85°. e
InAs (004) peak and its full width at half maximum (FWHM) are shown in Fig.1e. e InAs (004) peaks of LH1,
LH2, and G1 were positioned at 61.08°, 61.04°, and 61.05° and the lattice constant from the peaks was 6.064 Å,
6.067 Å, and 6.066 Å, respectively. e lattice constants are slightly larger than those of InAs, at 6.058 Å, and the
epitaxial InAs lms are almost relaxed. e threading dislocation density of the InAs lm in the G1 sample is
9.4 × 107/cm2, which was calculated by Ayer’s model in XRD spectra.
e 500 nm thick InAs lm in G1 was lattice mismatched to the GaAs by 7.32% out of plane. is means that the
lattice of InAs lms was stretched out of the plane. e FWHM of G1 was wider than that of LH1 and LH2, while
the G1 sample showed the highest electron mobility among these samples. e electron-defect scattering of the G1
sample was minimized due to the relatively low defect density in these samples. erefore, the stress induced by the
Figure 1. Growth schemes of InAs lms on a GaAs substrate and their structural and electrical properties. (a)
Schemes of sample growth using In0.87Al0.13As - In0.87Al0.13As (LH1), InAs - In0.87Al0.13As (LH2), InxAl1−xAs
graded (G1), and In0.87Al0.13As terminated (GT) buer layers on GaAs substrates. (b) Electron mobility and
surface roughness of the samples. (c) Surface morphology, obtained atomic force microscopy (AFM), of the
samples. e scale bar is 5 μm. (d) XRD 2θ/ω spectra of the samples. e dashed line indicates the InAs (400)
peak position. (e) InAs (400) 2θ/ω peak and its full width at half maximum (FWHM).
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lattice mismatch between InAs and GaAs relaxes by the deformation of the atomic structure of InAs in the G1 sam-
ple, while the stress relaxes by sliding and the generation of dislocations in the LH1 and LH2 samples.
e InAs p-i-n photodetector sample grew on an InxAl1−xAs graded buer layer in the G1 scheme. e p- and
n-type InAs lm grew with Be and Si at a doping concentration of 3 × 1018/cm3 and 5 × 1017/cm3, respectively. e
structural scheme and the TEM dark-eld image of the p-i-n InAs lm are shown in Fig.2a,b, respectively. e
AlAs and InxAl1−xAs layers are not clearly distinguishable, but the thickness of the layers in total is approximately
730 nm. Also, a high density of defects is shown in the layers.
Meanwhile, the thickness of the InAs p-i-n layer was 2370 nm, and some edge dislocations appeared as defects in
the TEM image. erefore, the graded buer layer suppressed the nucleation and sliding of the dislocations, inducing a
lattice mismatch between the InAs lm and the GaAs substrate, and the dislocations connes to the graded buer layer.
e brightness in a HAADF image indicates the number of electrons scattered inelastically by the atoms in a
sample, and the heavy atoms appear to be brighter than the light atoms. Figure2c exhibits a high angle annular
dark eld (HAADF) image of the InAs p-i-n sample with an AlAs layer of ~110 nm, and distinctly shows the
InAlAs layer of ~620 nm in thickness due to the dierence in brightness. Furthermore, the brightness increases
from the surface of the AlAs layer to that of the InxAl1−xAs graded buer layer, which implies that the Al and In
compositions have gradually changed in the buer layer. e white circles dissipate In rich droplets during the
focused ion beam (FIB) milling process in the InAs p-i-n region. e interface between the InxAl1−xAs graded
buer and the InAs p-i-n layer is rugged and corresponds to the pyramidal shaped surface of the GT AFM image,
as shown in Fig.1c.
e limited In diusion results in a dierence in growth rates along the (001) and (111) faces due to the
atomic density in these directions. e low growth temperature limits dislocation motion and increases yield
strength26,27. us, structural deformation is more benecial than the sliding and nucleation of the dislocations to
mitigate stress caused by the lattice mismatch and induced by the low growth temperature. Similarly, the disloca-
tions reect in the interface between the InAs and InAlAs graded buer layer.
e TEM image of the InAs/InxAl1−xAs graded buer/AlAs/GaAs, obtained by two beam conditions, is shown in
Fig.2d, and the black circles in the InAs are the In rich droplets. e mist and threading dislocations appear in the
lower region of the InxAl1−xAs graded buer layer, and the dislocations generated in the lower region have slipped.
In this case, the dislocation density decreases with increasing lm thickness. Meanwhile, the dislocation density in
the upper region of the InxAl1−xAs graded buer layer decreases as the InAs layer closes through threading disloca-
tion blocking by mist dislocation segment and fusion process. In addition, the dislocations in the upper region of
the InxAl1−xAs graded buer layer almost do not slip directly to the InAs layer. In other words, the dislocations are
conned in the InxAl1−xAs graded buer layer. e localization of the dislocations is attributed to the abrupt inter-
face28,29. e connement of dislocations is also shown in Fig.2b, where point A is explained by Fig.2f.
Figure 2. Structural diagram and micro structure analysis of p-i-n inas on a GaAs substrate. (a) Scheme of the
p-i-n InAs on a GaAs substrate. (b) Transmission electron microscopy (TEM) dark-led image of p-i-n InAs
on a GaAs substrate. (c) High angle annular dark eld (HAADF) image of p-i-n InAs on a GaAs substrate. (d)
High-resolution TEM image of the InAs/InAlAs graded buer/AlAs/GaAs substrate. e A point indicates
the change in the rate of increase in the in-plane strain, as shown in the strain line prole (f). e image shows
threading dislocations blocked by mist dislocation segments, and threading dislocation fusions in white
circles. (e) Energy-dispersive X-ray spectroscopy (EDS) elemental line prole of p-i-n InAs on a GaAs substrate.
(f) In-plane and out-of-plane strain line prole of p-i-n InAs on a GaAs substrate. e A point indicates the
point in the TEM image (d).
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e normalized EDS line prole is illustrated in Fig.2e. e amount of Al and In gradually decreases and
increases, respectively, along the growth direction, as expected with an InxAl1−xAs graded buer layer. e change
in the In and Al composition in the graded buer layer is consistent with the increased brightness in the HADDF
image shown in Fig.2c. As noted, this brightness relates to the atomic mass.
e strain line prole of the InAs p-i-n sample is shown in Fig.2f and is relatively obtained to the lattice
constant of GaAs substrate by the Topspin experiment. e inset of Fig.2f shows the enlarged strain prole of
the InxAl1−xAs layer in the sample. Here, sxy and szz indicate the in-plane (110) and out-of-plane (001) strain,
respectively. e szz in the AlAs layer increases slightly, while sxy has almost no change. is means that the stress
induced by the lattice mismatch between the GaAs and AlAs is alleviated by the deformation of the AlAs cubic
structure. e sxy and szz gradually increase in the InxAl1−xAs graded buer layer, and the increased rate of strain
is conformable, from the AlAs to point A.
e similar increase in the rates of sxy and szz in the lower region of point A attributes to stress relaxation
caused by the generation and sliding of dislocations. On the other hand, the szz rate of increase is faster than that
of sxy in the upper region of point A. e dierence in rates between sxy and szz is attributed to the deformation of
the InxAl1−xAs cubic structure. erefore, the stress in the upper region of point A is dominantly relieved by the
deformation of the cubic structure rather than the generation and sliding of dislocations. In other words, for stress
relaxation, the generation and sliding of the dislocations is advantageous in the lower part of point A, while the
deformation of the cubic structure is advantageous in the upper part of point A.
At the interface between the graded buer layer and the InAs layer, szz and sxy are 7.45% and 7%, respec-
tively. e szz is in good agreement with the XRD result, which is approximately 7.32%. As the thickness of InAs
increases, the dierence between the sxy and szz strain gradually decreases until the szz and sxy are about 7.45%
and 7.35%, respectively, at the surface of the InAs layer. Although the strain of InAs against GaAs is larger than
the original strain of 7.25%, the gradual equalization of the strains implies that the atomic structure of InAs has
recovered from the deformed cubic to the cubic form.
Figure3 shows the electrical and opto-electrical properties of the fabricated detector. Figure3a exhibits
the current density versus bias (J-V) curve of the detector measured at room temperature, and shows the
rectication characteristics of the p-i-n junction. e dark current density of the InAs photodetector, meas-
ured at room temperature under a bias of −0.5 V, is 4.6 A/cm2 as shown in Fig.3b. It is slightly lower than
those of other InAs photodetectors (PDs) on a GaAs substrate. e dark current densities of InAs PDs, which
were grown using a LT-InAs and an InAlAs graded buer layer, are 9.4 A/cm2 and 7 A/cm2, respectively22.
Furthermore, it is worth noting that these values are approximately two orders of magnitude higher than that
of 0.064 A/cm2 from a homo-epitaxial InAs photodetector due to the dependence of the dark current density
on the dislocation density30.
Figure3c shows the normalized photoresponse of the detector as a temperature variation, and the cut-o
wavelength is red-shied from about 3.1 μm at 77 K to 4 μm at 300 K. e changed cut-o wavelengths relates to
the band gap of InAs at various temperatures. e peak responsivity is shown in Fig.3d and its value varies from
0.6 A/W at 80 K to 0.126 A/W at 300 K. e detectivity (D*) of the photo-detector is given by
=









⁎
DR
RA
kT4(1)
p0
1/2
where k, T, and A are Boltzmann’s constant, temperature, and the window of the device, respectively.
e D* of the InAs photodetector at room temperature is estimated by Eq. (1) to be 1.65 × 108 cm · Hz1/2 · W−1
at 3.3 μm.
In order to verify the imaging capability of the InAs photodetector, 2D image scanning was performed by
means of a bi-axial mechanical scanner. Figure3e depicts a schematic diagram of a single-pixel imaging system
in a transmissive conguration used for 2D imaging in the short wave infrared (SWIR) range. Since the InAs
photodetector was used as a single-pixel sensor, a bi-axial mechanical scanner was used to obtain 2D images.
Also, two linear stages (Physik Instrument, Q-545) were used to scan the x and y axes, respectively. e 2D
photo-detection mapping image was obtained using a ltered IR-light source with a band-pass lter, and an open-
work thin Sherlock Holmes bookmark was used as a scanning object. e position of the scanned object was in
the plane where the image of the pinhole spot was formed by the use of lenses. erefore, the output images can
be obtained by scanning the spot through the scanned object. e scanned object was attached to the x-y planar
moving stage, and the object was scanned and captured by the single-pixel InAs photodetector. A source meas-
urement unit (Keysight Technologies, B2901A) was used to measure photocurrents. Each pixel value corresponds
to the current measurement obtained at the corresponding scanner position.
e 2D mapping images of the photo-detection are shown in Fig.3f. A band-pass lter with an FWHM of
0.5 ± 0.1 μm lters the light source. e 2D mapping image with a 2250 nm lter is brighter than that of a 2500 nm
lter, but a stronger photoresponse is attributed to the spectral dependence of the light-source power. Despite the
dierences in photoresponse, the Sherlock Holmes image is clearly displayed, which means that the InAs p-i-n
photodetector, grown using the InxAl1−xAs graded buer layer, can be used as an image sensor for the MIR region.
Conclusion
To obtain a high quality InAs lm, we investigated an InAs lm grown on a GaAs substrate using a LT-HT and
graded buer layer. e InAs lm with the graded buer layer exhibited the highest electron mobility among the
lms and its value is 9,275 cm2/V·s. e InAs p-i-n photodetector on a GaAs substrate grew using an InxAl1−xAs
graded buer layer (x = 0 → 0.87). e cut-o wavelength of the detector is approximately 4 μm and the respon-
sivity is 0.126 A/W at room temperature.
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Figure 3. Performance of the InAs photodetector. (a) Current density-voltage (J-V) curve of the fabricated
InAs photodetector, measured at room temperature. (b) Dark current density values reported by others, at a
bias of – 0.5 V at room temperature. (c) Photoresponse of the InAs photodetector at various temperatures. e
cut-o wavelength is simultaneously red-shied by increasing temperature. (d) Peak responsivity of the InAs
photodetector at various temperatures, measured by a blackbody temperature of 700 °C and chopper frequency
of 500 Hz. e detectivity (D*) is obtained using Eq. (1). (e) Schematic illustration of the single-pixel imaging
system in a transmissive conguration used for 2D imaging in the short-wave infrared range. (f) 2D photo-
detection images at the peak wavelengths of 2.25 μm and 2.5 μm, ltered by band-pass lter.
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In future work, we will focus on the research of the integration of InAs photodetectors with wafer bond-
ing and epitaxial li-o method, because the InAlAs/AlAs graded buer was designed for selective etching31.
Additionally, the InAs photodetector will be optimized.
Methods
Electrical properties such as resistivity, carrier mobility, and carrier concentration were measured by an Ecopia
HMS-3000 Hall Measurement System with an input current of 0.1 mA at room temperature.
The InAs surface and morphology were measured using a Park systems XE-100 with an NSC-36 tip in
non-contact mode.
e lattice spacing on the out-of-plane samples was measured using a Rigaku ATX-G XRD.
e microstructure was studied using a TECNAI F20 G2 SuperTwin TEM (FEI, Hillsboro, OR) with the
sample mounted in a double-tilt holder (Gatan, Pleasanton, CA). TEM images were obtained by the Fischhione
Model 3000 ADF detector and UltraScan 1000 (2k × 2k) CCD camera (Gatan Inc.). Energy dispersive spectros-
copy (EDS) and TopSpin analysis, which are strain analysis tools, were performed using a Talos F200X TEM with
Bruker Super EDS system and NanoMEGAS DigiSTAR precession electron diraction (PED) unit with Appve
soware in TENCAI F20 G2 SuperTwin TEM, respectively.
e current density of the 500 × 500 μm detector was measured at 300 K by a Keithley 4200 integrated in a
probe station. e photocurrent spectra were obtained using a customized system with a Bruker VERTEX 80 v
Fourier transform infrared spectrometer, a global MIR source, a Janis cryo-chamber, and a Keithley 428 low-noise
current amplier. e peak responsivity was measured using a fully-integrated smart home system with a 700 °C
blackbody source, vacuum chamber, and SR830 lock-in amplier for a 77 K low temperature experiment.
For 2D imaging, the optical wavelength range from an IR-source (SLS202L, Thorlab) was filtered by a
band-pass lter (FB2250-500 or FB2500-500, orlab), and then the optical path was passed to the single InAs
p-i-n photodetector or masked by a Sherlock Holmes bookmark supported by an XY automated stage. e exper-
iment was carried out at room temperature.
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Acknowledgements
is work was mainly supported by KIST Institutional Program (2E29390).is work was partially supported
byNRFgrant funded by the Korea government(MSIP) (No. 2019M3F3A1A02072069).
Author Contributions
Jin Dong Song managed the research and supervised the experiment. Soo Seok Kang grew the samples and
analyzed the experiments. Suk-Ho Choi proofread the manuscript. Dae-Myeong Geum, Sang Hyeon Kim and
Won Jun Choi fabricated and analyzed performance of the InAs photodetector. Cheol-Hwee Shim and HyeYoung
Hyun carried out TEM measurements. Kisung Kwak and Min-Chul Park carried out and analyzed the 2D
imaging experiment. All authors reviewed the manuscript. Ji-Hoon Kang provided exact expression and modied
gure 3e of image scanning.
Additional Information
Supplementary information accompanies this paper at https://doi.org/10.1038/s41598-019-49300-z.
Competing Interests: e authors declare no competing interests.
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