Development of high performance 1280×1024 InGaAs SWIR
FPAs detector at room temperature
Jiaxin Zhang1,2, Wei Wang1,2, Zaibo Li1, Haifeng Ye1, Runyu Huang1, Zepeng Hou1, Hui Zeng1,
Hongxia Zhu1, Chen Liu1, Xueyan Yang1, Yanli Shi1*
1
School of Physics and Astronomy, Yunnan University, Kunming 650504, China
2
Shanxi Guohui Optoelectronic Technology com., LTD Taiyuan 030006, China
*Corresponding author. E-mail:ylshikm@hotmail.com (Yanli Shi)
Abstract ：The 1280×1024 In0.53Ga0.47As short wave infrared (SWIR)focal plane array (FPA)
detector with planar-type back illuminated process has been fabricated. With indium bump Flip chip
bonding techniques, the InGaAs photodiode array (PDA) was hybrid- integrated to the CMOS
Readout Integrated Circuit (ROIC) with Correlated Double Sampling (CDS). The response spectral
is 0.9μm-1.7μm. The test results show that the dark current density is 2.25nA/cm2 at 25℃, the
detectivity D*is up to 1.1× 1013cm · Hz1 / 2 / W and the noise electron is as low as 48e- under CDS
mode, the quantum efficiency (QE) is 88% at 1550nm, and the operability is more than 99.9%.
Moreover, the dark current and noise electron have been studied theoretically in depth. The results
indicate that the diffusion current is the main contribution of the dark current, and the ROIC noise
electron is the main source of FPA noise.
Keywords: InGaAs SWIR FPA, ROIC, Flip chip bounding, Dark current, Quantum efficiency
1. Introduction
PIN InGaAs shortwave infrared (SWIR) focal plane arrays (FPAs) detectors have attracted
extensive attention due to high detectivity [1], high quantum efficiency, room temperature operation,
low dark current and good radiation resistance [2]. Furthermore, InGaAs FPAs detectors have wide
applications in many fields, such as aviation safety [3], biomedicine [4], camouflage recognition [5],
infrared night vision [6]. Recently, InGaAs SWIR FPAs detector is developing to reduce the pitch
and enlarge the format [7.8]. Aerius Photonics reported the 1280×1024 20μm InGaAs FPA detector.
The dark current density was 3.85A/cm-2 at 25℃, and the operability was 99.88% [9]. SCD developed
the 1280×1024 with pitch10μm InGaAs FPA detector. The quantum efficiency (QE) at 1550nm was
80%. The dark current density was 0.5nA/cm2at 7℃, and the operability was 99.5% [10]. FLIR
researched and developed 1280×1024 15μm InGaAs detector. The QE was up to 70%. The noise
electron was as low as 70e- in middle gain at 20℃, and the operability was up to 99.5% [11]. For
space application, it is critical to develop large format PIN arrays with small pitch and low dark
current density at higher operation temperature. However, dark current density reported up to now
is more than 3nA/cm-2 at room temperature, and lower dark current density is required to gain higher
sensitivity which is very important for low light level applications.
The lattice matching of In0.53Ga0.47As with InP substrate constitutes a significant advantage to
limit defects densities and then reduces Shockley Read Hall (SRH) generation-recombination dark
currents. The high crystalline quality material is the key point to reduce the dark current. Besides,
Zn diffusion depth is another process that affects dark current. if Zn diffusion depth exceeds the
InP/InGaAs hetero-interface, the InGaAs is damaged and dot defects are caused by Zn impurity.
The dot defects become carrier recombination centers in InGaAs absorption layer, resulting in
increasing dark current. Therefore, the Zn diffusion depth should reach InP/InGaAs herero-interface
precisely [12]. In this paper, the fabrication of high performance 1280 × 1024 InGaAs SWIR FPA
detector with pitch 15μm is presented. The device was processed with planar-type back illuminated
process by flip chip bounding with indium bump. The EPI material quality was optimized and the
Zn diffusion depth was controlled precisely to reduce dark current. The test results show that the
dark current density is 2.25nA/cm2 at 25℃, the operability is up to 99.98%, and the QE is 88% at
1550nm. Moreover, the contribution of various dark current and noise electronic mechanisms are
analyzed theoretically.
2. Fabrication of InGaAs SWIR FPA
2.1 EPI structure growth
The typical PIN InGaAs/InP heterostructure was grown by Metal Organic Chemical Vapor
Deposition (MOCVD) on 4 inches n+ type InP substrates. The EPI structure consisted of 0.4 μm n+InP buffer layer, 2.8 μm In0.53Ga0.47As absorption layer, and a 1 μm n-InP cap layer. Defect density
of the EPI was 0.1/cm2.
2.2 InGaAs FPA fabrication
The developed design of InGaAs FPA is common for all array formats. The active region is
composed of PIN photodiodes and surrounded by common N-contact pixels to apply uniform
polarization voltage. Firstly, a SiN layer was deposited on the EPI wafer by ICPECVD after preclean with 1%HCl, then the Zn diffusion hole was fabricated with SiN dry and wet etch, and Zn
diffusion with Zn3P2 in tube, Fig. 1 is cross-section of Zn diffusion. After that, the second SiN layer
was deposited on the wafer for Zn activation anneal and SiN dry etch for p-metal evaporation.
Secondly, The InP and InGaAs around the active region was etched to exposed n+-InP buffer layer
for n-type metal evaporation with E-beam, then P metal and n-metal were annealed for ohmic
contact. Thirdly, the connect metal was deposited with E-beam, and then InP substrate was lapped
and polished for anti-reflection coating (ARC) layer deposition, Fig. 2 is cross-section of PDA.
Fourthly, indium bump evaporation and reflow, Fig. 3 is the In bump after reflow. During the whole
process, the Zn diffusion depth was controlled to the InGaAs/InP hetero-interface precisely by
optimizing the diffusion time and temperature. The contact resistance of P-metal and N-metal are
2.69×10-5Ω·cm2 and 2.81×10-7Ω·cm2, respectively. Finally, after wafer dicing, the InGaAs PDA was
hybrid-integrated to CMOS ROIC with indium bump by flip chip bonding. The ROIC circuit adopts
snapshot mode, supporting integrated readout (ITR) and integral simultaneous read (IWR) mode,
and CDS mode. CDS mode is used to reduce KTC noise and FPN noise. Fig. 4 is the ROIC circuit.
The packaged 15μm 1280×1024 InGaAs FPA detector was packaged with high vacuum integrity
metallic package and themo electric cooler (TEC). Fig. 5 is the packaged FPA chip. Moreover, the
smaller format 640×512 15μm InGaAs SWIR detectors with similar processing were applied in
space exploration in 2019.
Fig. 1. Cross-section of Zn diffusion
Fig. 2. Cross-section of PDA
Fig. 3. The In bump after reflow
Fig. 4. The circuit of ROIC
Fig. 5. Packaged FPA chip
Fig. 6. The dark value versus exposure time
Fig. 7. Histograms of the dark current at 33℃
2.3 Test result
With Pulse Instruments 7700 FPA test system and EMVA 1288 standard, we tested the
electrical characteristics and spectral response characteristics of the detector. The operability is up
to 99.98%. The response non-uniformity is 4.2%. The quantum efficiency is 88% @1550nm. The
detectivity D * reaches 1.1 × 1013cm · Hz1 / 2 / W under CDS mode, and the readout noise electron
is 48 e- under CDS mode. The dark current density is measured as low as 2.25nA/cm2 and
5.06fA/pixel @ 25℃，as shown in Fig. 6. Besides, the histogram of the dark current is shown in
Fig. 7, which is from the third party, the mean dark current of pixels is about 10 fA/pixel at 33℃.
Because of the high temperature, the result is different from what we measured. But both results
indicate that the dark current is very low. The dynamic range is 64dB. The responsivity is 1.1A/W.
Table1 is the performances compare with other detectors.
Table1 Performance comparison of 1K×1KInGaAs FPA
R & D unit
Spectrolab[14]
SUI[15]
Dark current
D*
(nAcm-2)
(cm·Hz1/2W-1)
QE
Operability
0.7@280K
>1013
80%
>99%
2@12.5℃
>1013
65%
>99%
FLIR[11]
<1@15℃
>1013
70%
>99.5
Aerius Photonics[9]
3.85@RT
>1013
80%
99.88%
SCD[10]
0.5@280K
>1013
80%
>99.5%
<5@RT
5.3×1012
75%
>99%
2.25@RT
1.1×1013
88%
>99.9%
SITP[8]
This work
3. Performance analysis
3.1 Dark current
Dark current is a key parameter which must be decreased to improve signal to noise ratio and
minimize the noise equivalent power. Dark current is composed of diffusion current, generaterecombination current, tunneling current, surface leakage current [13]. Dark current density Jexp is
2.25nA/cm2 at -0.1V with EMVA1288 standard, as shown in Fig. 6. The dark current was measured
on test cells for photodiode diameters varying from 6 μm to 200μm, as shown in Fig. 8. Diffusion
current density Jdiff and generated-recombined current density Jgr are calculated with the Formulae
(1) and (2)[13], respectively, Intrinsic carrier concentration ni is given by formula (3) and depletion
width Wd is given by formula (4)[13]. The result is shown in Fig. 9. At -0.1V, the diffusion current
density Jdiff is 1.82nA/cm2 and the generated-recombined dark current density Jgr is 0.39nA/cm2.
Hence, the diffusion current density Jdiff is the main contribution of the dark current density. The
generated-recombined dark current density Jgr is about one fifth of the diffusion dark current density.
Consequently, the gap between Jtotal and Jexp is tunneling current density and the surface leak current
density, but the gap becomes bigger with reverse bias increase, this is because tunneling current is
linear with reverse bias, then Jexp increase faster than Jtotal with reverse bias increase. Besides, the
dark current density can be expressed as formula (5)[14], where P is the pixel perimeter and A is
the pixel area, Jb is the bulk current, and Js is the surface-related current. Fig.10 shows Jd vs. P/A
taken from variable size test diodes at room temperature. Js, the slope of fitting line, is 0.3pA/cm,
Jb, the intercept of fitting line, is 2.29nA/cm-2. Therefore, we could eliminate influence of surface
leak current. The results indicate good surface passivation by SiN and precise Zn diffusion process.
𝑞𝑉
𝐽𝑑𝑖𝑓𝑓 = 𝑞𝑛𝑖2 𝐻(𝐵 + 𝐶𝑁𝑑 + (𝑁𝑑 𝜏 𝑆𝐻𝑅 )−1 ) (𝑒 𝐾𝑇 − 1)
(1)
𝑞𝑉
𝑞𝑛 𝑊
𝑖 𝑑
𝐽𝑔𝑟 = 𝜏𝑆𝐻𝑅
[𝑒 2𝐾𝑇 − 1]
(2)
𝐸𝑔
𝑛𝑖2 = 𝑁𝑐 𝑁𝑉 𝑒 −𝐾𝑇
𝑊𝑑 = [
(3)
1
2𝜀0 𝜀𝑠 (𝑉0 −𝑉) 2
𝑞𝑁𝑑
(4)
]
𝑃
(5)
𝐽𝑑 = 𝐽𝑠 𝐴 + 𝐽𝑏
where q is electric quantity, ni is intrinsic carrier concentration of InGaAs, H is thickness of InGaAs,
B is radiation recombination coefficient, C is Auger recombination coefficient, Nd is doping
concentration of InGaAs, τSHR is the SHR lifetime, V0 is the voltage of built-in electric field, V is
the bias, k is the Boltzmann constant, T is temperature, Nc is effective conduction band density of
states, Nv is effective valence band density of states, Eg is energy gap. All the parameters used are
in Table 2.
Table 2 Parameters used in calculation[13]
Eg
Nc
Nv
B
C
τSHR
（cm-3）
eV
（cm-3）
（cm-3）
（cm3/s）
（cm3/s）
（s）
InGaAs
2×1015
0.74
2.1×1017
7.7×1018
9.5×10-11
8.1×10-29
4×10-4
13.9
InP
2×1017
1.34
5.7×1017
1.1×1019
1.2×10-10
9×10-31
1×10-9
12.5
material
Nd
Fig.8. Dark current versus bias
εs
Fig.9. Dark current density versus reverse bias
Fig.10. Dark current density versus P/A
3.2 Noise electron
The noise electron of InGaAs FPA contains PDA noise, ROIC noise and the couple noise of
PDA and ROIC. The PDA noise comes from thermal noise and the shot noise of dark current. the
ROIC noise electron and FPA noise electron are measured under CDS mode and non-CDS mode,
respectively. The results show the ROIC noise electron is 42e-, and the InGaAs FPA noise electron
is 72 e- under non-CDS mode, while the ROIC noise electron is 20e- and the InGaAs FPA noise
electron is 48e- under CDS mode. The thermal noise electron Nthermal and the shot noise electron
Nin,shot were calculated with the formula (6) and (7)[13], respectively.
2𝐾𝑇
2
Nthermal
= 𝑞2𝑅 𝑇𝑖𝑛𝑡
(6)
𝑑
𝐼
2
Nin，shot
= 𝑞𝑑 𝑇𝑖𝑛𝑡
(7)
where q is the electric quantity, k is the Boltzmann constant, T is temperature, Id is the dark
current, Rd is the resistance of pixel, Tint is the integration time.
The calculation results of thermal noise and the shot noise of dark current are about 14 e- and
11 e-, respectively. The PDA noise electrons are 25e- at room temperature. Compared with the actual
measurement results in Table 3, it is revealed the PDA noise is the main contribution of FPA noise
under CDS mode, while the ROIC noise is the main contribution of FPA noise under non-CDS mode
operation.
Table 3 Noise measurement results of FPA and ROIC
mode
ROIC noise
FPA noise
With CDS
20 e-
48 e-
Without CDS
42 e-
72 e-
3.3 Detectivity D*
The detectivity D*is up to 1.1×1013cm﹒Hz1/2/W and the signal noise ratio（SNR）is 64dB
under CDS mode. But under non-CDS mode the detectivity D*is 4.2×1012cm﹒Hz1/2/W, and the
SNR is 52 dB. According to the previous analysis of readout noise electron, the FPA readout noise
electron under CDS mode is lower than that under non-CDS mode, which causes the SNR under
CDS mode larger than that under non-CDS mode. Therefore, as shown in formula (7), the D* is
higher under CDS mode than that under non-CDS mode. The ROIC noise is the main reason that
causes the SNR and the detectivity D* lower.
1
𝑅
𝐷 ∗ = 𝑁𝐸𝑃 = 𝑉𝑉 √𝐴𝑑 ∆𝑓
𝑛
(8)
Where NEP is the noise equivalent power, Rv is the response voltage, Vn is the noise voltage,
Ad is the photo-sensitive area of pixel, Δf is the noise equivalent bandwidth.
4. Conclusion
In summary, the high performance 15μm 1280 × 1024 InGaAs PIN short wave infrared detector
was fabricated by optimizing the EPI material quality and the Zn diffusion depth. The results
indicate that the dark current is as low as 2.25nA/cm-2 at room temperature. The response nonuniformity is 4.2%. The operability is more than 99.9%, the detectivity D*is up to 1.1×1013cm﹒
Hz1/2/W, and the SNR is 64dB under CDS mode operation. The calculated noise electron of PDA is
25e-, which is the main contribution of FPA noise. Owing to larger noise from ROIC under nonCDS mode, the detectivity is 4.2×1012cm﹒Hz1/2/w, and the SNR is 52dB. The test results show the
ROIC noise is the main reason that causes the SNR and the detectivity D* lower under non-CDS
mode. In addition, the theoretical calculation data of dark current shows that the diffusion current is
the main contribution of dark current.
References
[1] H. J. Gao, Y. H. Zhou, Recent progresses in InGaAs visible/short wavelength infrared
focal plane array detectors[J]. Infrared and Laser engineering 2007, (4): 431-434.
[2] X. M. Shao, H. M. Gong, X. Li, et al. Development of high performance short-wave Infrared
InGaAs focal Plane Detectors[J]. Infrared Technology 2016, 38 (8):629-635.
[3] Y. Cao, W.Q. Jin, X. Wang, et al. Development in Shortwave Infrared Focal Plane Array and
Application[J]. Infrared Technology 2009, 31(2):63-68.
[4] M. P. Hansen, D. C. Malchow, Overview of SWIR detectors, cameras, and applications[C]//
Thermosense XXX. International Society for Optics and Photonics, 2008. 6939: 0I-1-11.
[5] S. Huang, M. O'Grady, J.V. Groppe, et al. A customizable commercial miniaturized 320×256
indium gallium arsenide short wave infrared camera[C]// Conference on Infrared Systems and
Photoelectronic Technology 20040802-03, 05 Denver, CO(US). Sensors Unlimited, Inc. 3490 US
Rte 1, Princeton, NJ, USA 08540, 2004.
[6] T. Martin, R. Brubaker, P. Dixon, et al. 640x512 InGaAs focal plane array camera for visible and
SWIR imaging[C]// Infrared Technology & Applications XXXI. International Society for Optics
and Photonics, 2005.
[7] J.H. Liu, X.J. Gao, X. Zhou, Developments and Perspectives of SWIR InGaAs focal plane
Arrays [J]. Semiconductor optoelectronics 2015(05):10-15.
[8] X. Li, X. M. Shao, T. Li, et al. Research progress of short wave infrared InGaAs focal plane
detectors [J]. Infrared and laser engineering2020(01):64-71.
[9] M. Macdougal, J. Geske, C Wang, et al. Low Dark Current In Ga As Detector Arrays for
Night Vision and Astronomy[C]. Infrared Technology & Applications XXXV, 2009.
[10] R. Fraenkel R, E. Berkowicz, L. Bykov, et al. High definition 10μm pitch In Ga As detector
with asynchronous laser pulse detection mode[C]. Infrared Technology & Applications XLII, 2016.
[11] A. D. Hood, M.H. Macdougal, D. Follman, et al. Large-format InGaAs focal plane arrays for
SWIR imaging[C]. Spie Defense, Security, & Sensing, 2012.
[12] R. Dewames, R. Littleton, K. Witte, et al. Electro-Optical Characteristics of P+ n In0.53 Ga0.47
As Hetero-Junction Photodiodes in Large Format Dense Focal Plane Arrays[J]. Journal of Electronic
Materials, 2015.
[13] G.Q. Cao, Basic research on Application of high sensitivity planar InGaAs short wave infrared
detector [D] 2016(5):96-100.
[14] P. Yuan, J.C. Boisvert, N. Karam, Low-dark current 1024x1280 InGaAs PIN arrays[C]//
Infrared Technology & Applications XL. International Society for Optics and Photonics, 2014.
[15] P. Dixon P, C. Li, M. Ettenberg, et al. Dual-band technology on indium gallium arsenide focal
plane arrays[C]. Proceedings of SPIE - The International Society for Optical Engineering,
2011: 150-154.
Conflict of interest
There is no conflict of interest.
Acknowledgements
This work was supported in part by Yunnan provincial major science and technology special foundation (2018ZI002).