Infrared detector development and characterization at NASA Langley Research Center will be reviewed. These detectors were intended for ground, airborne, and space borne remote sensing applications. Discussion will be focused on recently developed single-element infrared detector and future development of near-infrared focal plane arrays (FPA). The FPA will be applied to next generation space-based instruments. These activities are based on phototransistor and avalanche photodiode technologies, which offer high internal gain and relatively low noise-equivalent-power. These novel devices will improve the sensitivity of active remote sensing instruments while eliminating the need for a high power laser transmitter

Abedin, M. N.

Amzajerdian, F.

Refaat, T. F.

Sulima, O. V.

NASA Technical Reports Server

Infrared detector activities at NASA Langley Research Center 
 
          M.N. Abedin1, T.F. Refaat2, O.V. Sulima3, and F. Amzajerdian1 
 
       1NASA Langley Research Center, Hampton, VA 23681 
2Old Dominion University, Norfolk, VA 23529 
   3University of Delaware, Newark, DE 19716 
 
 
ABSTRACT 
 
Infrared detector development and characterization at NASA Langley Research 
Center will be reviewed. These detectors were intended for ground, airborne, and space 
borne remote sensing applications. Discussion will be focused on recently developed 
single-element infrared detector and future development of near-infrared focal plane 
arrays (FPA). The FPA will be applied to next generation space-based instruments. These 
activities are based on phototransistor and avalanche photodiode technologies, which 
offer high internal gain and relatively low noise-equivalent-power. These novel devices 
will improve the sensitivity of active remote sensing instruments while eliminating the 
need for a high power laser transmitter. 
 
 
INTRODUCTION 
 
NASA’s Earth Science Technology Office and Science Mission Directorate show 
great interest in broadband detectors for numerous critical applications such as 
temperature sensing, process control, and atmospheric monitoring of trace gases (CO2, 
H2O, CO, and CH4). When selecting a detector for such applications, key parameters, 
must be considered in order to satisfy the requirements of the Earth and planetary remote 
sensing systems. These parameters include spectral response, quantum efficiency, noise-
equivalent-power (NEP), and gain. In general, large format focal plane arrays (FPA) in 
the 1.0- to 2.5-μm spectral range are the detectors of choice for the next-generation Earth 
and Space Science remote sensing, Mars Orbiter, and planetary instruments. An 
Antimonide (Sb)-based heterojunction phototransistor (HPT), as a suitable candidate, 
stimulates a strong interest for broadband remote sensing applications [1-4]. Besides p-i-n 
photodiodes and avalanche photodiodes (APD), HPTs have also attracted a great 
attention to satisfy many of the detector requirements for these applications without 
excess noise and high bias voltage problems, while maintaining superior NEP. HPT has 
an internal gain mechanism that allows increasing the output signal and signal-to-noise 
ratio (SNR). However, further reduction of gain related noise is desirable, and research 
on different HPT structures indicates some important design considerations that can 
minimize device noise and further increase the SNR. 
On the other hand, APDs are integrated solid-state semiconductor devices that 
manufactured using different materials. The common near-IR InGaAs/InP APDs are 
operational in the spectral range of 0.9 to 1.6 μm [5-7]. Recently, a group from DRS 
Technologies demonstrated responsivity of ~ 15 A/W using HgCdTe electron (e-) APD at 
https://ntrs.nasa.gov/search.jsp?R=20080014304 2019-08-30T04:14:57+00:00Z
short wave infrared (SWIR) wavelength (at -7 V and 20oC) [7]. However, HgCdTe e- 
APDs have demonstrated very high responsivity in the 3- to 5-μm range and their SWIR 
responsivity was low [7]. Even though HgCdTe detectors are efficient in the infrared 
range, significant technology limitations curb their application in that range. Therefore, 
researchers have been looking to other III-V systems that provide much higher yield by 
manufacturing and higher operability. In this context, it is necessary to explore alternative 
material systems, which can absorb radiation in the 1.0- to 2.5-μm range and are 
compatible with general requirements of a low-noise detector. InGaAsSb/AlGaAsSb 
heterostructures are very suitable for this application, and single-element HPTs based on 
these heterostructures demonstrated record responsivitites [3, 4, 8-14]. 
Quaternary InGaAsSb/AlGaAsSb HPTs in the 1.0- to 2.5-μm wavelength range have 
been developed and fabricated at AstroPower, Inc. in collaboration with NASA Langley 
Research Center (LaRC). These devices have been characterized at NASA LaRC and 
encouraging results have been obtained, including high responsivity, high detectivity, and 
relatively low NEP [3,4, 8-14]. Development of large-format Sb-based phototransistor 
FPA will enhance the capability of space-based active and passive remote sensing 
imaging systems and enable major advances in Astronomical, Earth, and planetary 
instruments. This new detector will enhance the capability of active remote sensing of 
CO2 and water vapor at 2.05 and 1.9 μm, respectively. 
There is no commercially available broadband detector with sufficient sensitivity in 
the 1.0- to 2.5-μm spectral range, whereas this spectral range is suitable for sounding 
Earth and planetary atmospheres. Therefore, we propose to develop the capability to 
reliably fabricate detector arrays that respond to broad near-IR wavelength regions.  
 
 
DEMONSTRATION OF SINGLE ELEMENT INFRARED DETECTOR 
 
Recently, NASA LaRC characterized single-element InGaAsSb/AlGaAsSb HPTs 
with a 200 μm diameter. Figure 1 shows the responsivity variation with wavelength in the 
0.6- to 2.4-μm range at different collector-emitter voltages and temperatures of such a 
device [11]. The responsivity is strongly dependent on wavelength, temperature, and bias 
voltage. A maximum responsivity of 10000 A/W was achieved at 1.9-μm, -193oC and 
5V. That was the highest responsivity ever reported in the 0.6- to 2.4-μm wavelength 
range for the Sb-based photodetectors. 
Figure 2 compares the NEP variation with bias voltage of a HPT and of commercial 
InGaAs p-i-n photodiodes (Hamamatsu; G5852 and G5853) at different wavelengths 
[10]. The photodiodes have different cutoff wavelengths: 2.6-μm for G5853 and 2.3-μm 
for G5852. It was determined that at 2 μm, NEP of G5852 (top solid lines at -20 oC) is 
about five times lower compared to G5853. Comparison with the best of the tested p-i-n 
photodiodes shows that at 4.0 V the HPT achieves near an order of magnitude lower NEP 
despite the 40 degrees higher operating temperature (20oC). Furthermore, this HPT was 
also operated at -20oC and NEP was reduced to 1.83x10-14 W/Hz 2
1
 at the same operating 
conditions. 
 
 
 
 600 1000 1400 1800 2200
10-2
100
102
104
Wavelength [nm]
R
es
po
ns
iv
ity
 [A
/W
]
20oC & 0V
20oC & 4V 70oC & 2V
-193oC & 0V
-193oC & 5V
R
es
po
ns
iv
ity
 [A
/W
]
 
 
Fig 1. Responsivity variation with wavelength at different bias voltages and temperatures 
for an HPT sample (A1-d2) [11].  
0 1 2 3 4
10-14
10-13
10-12
10-11
10-10
2.20 μm at 20oC
2.05 μm at 20oC
1.55 μm at 20oC
1.00 μm at 20oC
2.05 μm at -20oC
G5853
G5852
Bias Voltage (V)
N
E
P 
(W
/H
z1
/2
)
N
E
P 
(W
/H
z1
/2
)
 
 
Fig 2. Comparison of the NEP variation with bias voltage between HPT and commercial 
p-i-n photodiodes [10]. The NEP of the p-i-n photodiodes were measured at 2 μm, 1.0 V 
and -20oC. 
In addition, commercial APDs were acquired and characterized at NASA LaRC. 
Spectral response measurements of InGaAs APDs from Perkin-Elmer (APD1 with 80 μm 
diameter) and Sensors Unlimited Inc./Goodrich (APD2 with 200 μm) were performed. 
Figure 3 shows responsivity curves as a function of wavelength of the InGaAs APDs and 
phototransistor. The selected biases for the APDs were 52.0 V and 53.4 V at 20oC as 
specified by the manufacturers and the bias voltage for HPT was 4.0 V at -20oC. These 
two APDs have similar cutoff wavelengths near 1.7-μm, but the HPT has the cutoff at 
approximately 2.1-μm. The following responsivities were determined: above 100 A/W 
(20oC and 53.4 V) for APD2 and about 85 A/W (20oC and 52.0 V) for APD1 at 1.6-μm 
wavelength; and about 260A/W (20oC and 3.0 V) and 1700 A/W (-20oC and 4.0 V) for 
phototransistor at 2.0-μm. These are the highest responsivities measured for those APDs 
and phototransistor at different breakdown and bias voltages at 20oC and -20oC, 
respectively. 
Figure 4 shows the NEP characteristics of the InGaAs APDs and of the HPT at 
different wavelengths and at the same bias voltage and temperature settings used for the 
spectral response measurements. The following NEP is determined: about 6x10-15 
W/Hz 2
1
 for APD1 (20oC and 52.0 V) and about 7x10-13 W/Hz 2
1
 for APD2 at 1.6- μm 
wavelength. For the HPT, the NEP is determined ~1.2x10-12 W/Hz 2
1  (20oC and 3.0 V) 
and ~ 4.6x10-14 W/Hz 2
1
 (-20oC and 4.0 V) at 2.0-μm wavelength. Comparison with the 
tested avalanche photodiodes measured at 20oC shows that at breakdown voltage, APD1 
achieves near two order of magnitude lower NEP than APD2 and one order of magnitude 
lower NEP than phototransistor, when it was cooled down to -20oC. We believe that these 
discrepancies are due to the higher noise of APD2 and phototransistor as compared to 
APD1. 
 
1.0 1.4 1.8 2.2
Wavelength (µm)
101
102
103
R
e
sp
on
si
vi
ty
 (
A
/W
)
APD1 @ 20oC & 52.0V
APD2 @ 20oC & 53.4V
HPT @ 20oC & 3.0V
HPT @ -20oC & 4.0V
R
e
sp
on
si
vi
ty
 (
A
/W
)
 
 
Fig 3. Spectral response variation of the APDs and the phototransistor with 
wavelength at different bias voltages and temperatures (20oC and -20oC). 
 
 1.0 1.4 1.8 2.2
Wavelength (µm)
10-14
10-13
10-12
N
E
P
 (
W
/H
z1/
2 )
APD1 @ 20oC & 52.0V
APD2 @ 20oC & 53.4V
HPT @ -20oC & 4.0V
HPT @ 20oC & 3.0V
N
E
P
 (
W
/H
z1/
2 )
 
 
Fig 4. Comparison of NEP between the APDs and the phototransistor at the same 
operating conditions (20oC and -20oC). 
  
The HPTs have longer wavelength sensitivity and a comparably short wavelength 
sensitivity, which is an attractive solution for the broadband imaging systems. The 
attraction to this solution is because the easiest way to acquire broadband imaging is to 
use a single detector array with simple optics and electronics. For commercial 
technologies (for example, Si-cutoff 1.1 μm and InGaAs: 1.7 or extended 2.6 μm 
detectors), each wavelength band requires a separate detector with appropriate dichroic, 
focusing optics, support electronics, cooling, and mounting hardware. These requirements 
for additional components increase the size of an imaging system, resulting in increased 
power consumption, weight, and cost. Therefore, the broadband approach is being 
pursued because it offers an advantage of simple, efficient, cost-effective, lightweight, 
and compact instrument design. Broadband phototransistor arrays proposed to the NASA 
Earth-Sun Systems Division (ESSD) technology program for the active and passive 
remote sensing instrument will operate in the spectral range of 0.6 – 2.5 μm and extend 
this technology to flight missions for next generation. For the broad-spectral active and 
passive instrument, we will select regions that cover only interest lines (e.g., CO2, CH4, 
H2O, CO) with higher resolution within those bands. 
 
 
FUTURE DEVELOPMENT OF NEAR-INFRARED DETECTOR FPA 
 
The record results achieved with discrete 200-µm diameter HPTs provide a base for 
designing and fabrication of arrays of these devices. However, fabrication of the arrays is 
a challenging task. It requires a very high level of homogeneity of InGaAsSb/AlGaAsSb 
epitaxial layers, including their thickness, doping and chemical composition. For this 
purpose we are planning to use the Molecular Beam Epitaxy (MBE) - growth method. 
This method provides precisely controlled and reproducible growth of the required 
multilayer InGaAsSb/AlGaAsSb/GaSb heterostructure on the area of up to 4 cm2.  This 
epitaxial growth was successfully used by the University of Delaware-NASA team for 
fabrication of the first room temperature HPT with the cutoff wavelength of 2.4 µm [15]. 
There are no reports regarding fabrication of arrays of Sb-based photodetectors with 
internal gain (APDs or phototransistors), and only few reports about SWIR arrays of 
InGaAs and HgCdTe APDs. For example; Sensors Unlimited developed 32 x 32 arrays of 
InGaAs APDs on a 100 µm pitch for 1.55 µm wavelength [16] and DRS reported about 
first HgCdTe APD arrays [17]. NASA LaRC is interested in 2-D arrays fabrication and 
hybridization in cooperation with the University of Delaware (UD) and a start-up 
company Advanced Optical Materials, LLC, related to the antimonide based 
phototransistors.  
 
 
SUMMARY 
 
We have demonstrated current single-element infrared detectors and future 
development of near-infrared focal plane arrays (FPA) for applications to next generation 
space-based instruments. Most of these activities are based on phototransistor technology, 
which is offering high internal gain and low NEP operation. Developed phototransistors 
showed higher responsivity and higher gain with a light collecting area diameter of 200-
micron. Spectral response measurements and NEP calculations were carried out to the 
phototransistor to achieve the responsivity at 2.0-µm and NEP is several times lower than 
commercially available state-of-the-art p-i-n photodiodes. On the other hand, 
phototransistor has achieved two-order-of-magnitude higher responsivity as compare to 
APDs, despite the higher NEP as compare to Perkin-Elmer APD and lower NEP with 
respect to SUI/Goodrich APD at near room temperature operation. These new 
phototransistors will improve the sensitivity of the passive remote sensing instruments 
and reduce the laser transmitter power for active remote sensing instruments, while 
eliminating the need for high breakdown voltage avalanche photodiode. 
 
 
REFERENCES 
 
1. P. Ambrico, A. Amodeo, P. Girolamo, and N. Spinelli, Applied Optics 39(36), 6847– 
6865 (2000). 
2. S. Ismail, G. J. Koch, B. W. Barnes, N. Abedin, T. F. Refaat, J. Yu, S. A. Vay, S. A. 
Kooi, E. V. Browell, U. N. Singh, Proceedings of the 22nd International Laser Radar 
Conference, 65-68 (2004). 
3. T.F. Refaat, M.N. Abedin, O.V. Sulima, S. Ismail, and U.N. Singh, Optical 
Engineering 43(7), 1647-1650 (2004). 
4. T.F. Refaat, M.N. Abedin, O.V. Sulima, U.N. Singh, and S. Ismail, IEDM Tech. Dig., 
355-358 (2004). 
5. V. Diadiuk, S.H. Groves, C.E. Hurwitz, and G.W. Iseler, IEEE J. Quantum 
Electronics, QE-17 (2), 260-264 (1981). 
6. J.C. Campbell, A.G. Dentai, W.S. Holder and B.L. Kasper, Electron. Lett. 19, 818-
820 (1983). 
7. K.K. Loi and M. Itzler, Compound Semiconductor 6(3), 1-3 (2000). 
8. O.V. Sulima, T.F. Refaat, M.G. Mauk, J.A. Cox, J. Li, S.K. Lohokare, M.N. Abedin, 
U.N. Singh, and J.A. Rand, Electronics Letters 40, 766-767, (2004). 
9. O.V. Sulima, T.F. Refaat, M.G. Mauk, J.A. Cox, J. Li, S.K. Lohokare, M.N. Abedin, 
U.N. Singh, and J.A. Rand, Presented at 6th Middle-Infrared Optoelectronics 
Materials and Devices (MIOMD) Conference, in St. Petersburg, Russia, 28 June-1 
July 2004. 
10. M.N. Abedin, T.F. Refaat, O.V. Sulima, and U.N. Singh, IEEE Trans. Electron 
Devices 51(12), 2013-2018 (2004). 
11. M.N. Abedin, T.F. Refaat, O.V. Sulima, and U.N. Singh, International Journal of 
High Speed Electronics and Systems, v.15, No.2, pp. 567-582, (2006). 
12. T.F. Refaat, M.N. Abedin, O.V. Sulima, S. Ismail, and U.N. Singh, Optical 
Engineering, v. 43, No. 7, pp.1647-1650 (2004). 
13. T.F. Refaat, M.N. Abedin, O.V. Sulima, U.N. Singh and S. Ismail, Technical Digest 
of the 50th IEEE International Electron Devices Meeting (IEDM), San-Francisco, Ca, 
December 2004, pp.355 – 358 (2004). 
14. T.F. Refaat, M. N. Abedin, O.V. Sulima, S. Ismail and U.N. Singh, Proc. SPIE, 
v.5887, pp.588706-1 – 588706-13  (2005). 
15. O.V. Sulima, K. Swaminathan, T.F. Refaat, N.N. Faleev, A.N. Semenov, V.A. 
Solov’ev, S.V. Ivanov, M.N. Abedin, U.N. Singh, and D. Prather, Electronics Letters, 
v.42 (1), pp. 55-56 (2006). 
16. J.C. Dries, T. Martin, W. Huang, M.J. Lange, and M. J. Cohen, IEEE LEOS 
Proceedings, 2002. 
17. J.D. Beck, C.-F. Wan, M.A. Kinch, and J.E. Robinson, SPIE v. 4454, pp. 188-197 
(2001). 
 


Infrared Detector Activities at NASA Langley Research Center

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