Effects of gamma and proton irradiation, and of forward bias minority carrier injection, on minority carrier diffusion and photoresponse were investigated for long-wave (LW) and mid-wave (MW) infrared detectors with engineered majoritycarrier barriers. The LWIR detector was a type-II GaSb/InAs strained-layer superlattice pBiBn structure. The MWIR detector was a InAsSb/AlAsSb nBp structure without superlattices. Room temperature gamma irradiations degraded the minority carrier diffusion length of the LWIR structure, and minority carrier injections caused dramatic improvements, though there was little effect from either treatment on photoresponse. For the MWIR detector, effects of room temperature gamma irradiation and injection on minority carrier diffusion and photoresponse were negligible. Subsequently, both types of detectors were subjected to gamma irradiation at 77 K. In-situ photoresponse was unchanged for the LWIR detectors, while that for the MWIR ones decreased 19% after cumulative dose of ~500 krad(Si). Minority carrier injection had no effect on photoresponse for either. The LWIR detector was then subjected to 4 Mrad(Si) of 30 MeV proton irradiation at 77 K, and showed a 35% decrease in photoresponse, but again no effect from forward bias injection. These results suggest that photoresponse of the LWIR detectors is not limited by minority carrier diffusion.
We report high quantum efficiency (QE) MWIR barrier photodetectors based on the InAs/GaSb/AlSb type II superlattice (T2SL) material system. The nBp design consists of a single unipolar barrier (InAs/AlSb SL) placed between a 4 μm thick p-doped absorber (InAs/GaSb SL) and an n-type contact layer (InAs/GaSb SL). At 80K, the device exhibited a 50% cut-off wavelength of 5 μm, was fully turned-ON at zero bias and the measured QE was 62% (front side illumination with no AR coating) at 4.5 μm with a dark current density of 8.5×10-9 A/cm2 . At 150 K and Vb=50 mV, the 50% cut-off wavelength increased to 5.3 μm and the quantum efficiency (QE) was measured to be 64% at 4.5 μm with a dark current of 1.07×10-4 A/cm2 . The measurements were verified at multiple AFRL laboratories. The results from this device along with the analysis will be presented in this paper.
In this work, we compare the performance of three MWIR unipolar barrier structures based on the InAs/GaSb Type-2 strained layer superlattice material system. We have designed, fabricated, and characterized pBiBn, pBn, and pBp detector structures. All the structures have been designed so that the cut off wavelength is around 5 microns at 100 K. We fabricated single-pixel devices and characterize their radiometric performance. In addition, we have characterized the degradation of the performance of the devices after exposing the devices to 63 MeV proton radiation to total ionizing dose of 100 kRad (Si). In this report, we compare the performance of the different structures with the objective of determining the advantages and disadvantages of the different designs. This work was supported by the Small Business Innovation Research (SBIR) program under the contract FA9453-14-C-0032, sponsored by the Air Force Research Laboratory (AFRL).
We present an approach to realize antimonide based superlattices on silicon substrates without using conventional
Indium-bump hybridization. In this approach, PIN based superlattice detectors are grown on top of a 60 nm Al0.6Ga0.4Sb
sacrificial layer on a GaSb host substrate. Following the growth, the individual pixels are transferred using our epitaxiallift
off technique, which consists of a wet-etch to undercut the pixels followed by a dry-stamp process to transfer the
pixels to a silicon substrate prepared with a gold layer. Structural and optical characterization of the transferred pixels
was done using an optical microscope, scanning electron microscopy and photoluminescence. The interface between the
transferred pixels and the new substrate was abrupt and no significant degradation in the optical quality was observed.
An Indium-bump-free membrane detector was then fabricated using this approach. Spectral response measurements
provided a 100% cut-off wavelength of 4.3 μm at 77 K. The performance of the membrane detector was compared to a
control detector on the as-grown substrate. The membrane detector was limited by surface leakage current. The proposed
approach could pave the way for wafer-level integration of photonic detectors on silicon substrates, which could
dramatically reduce the cost of these detectors.
The Interband Cascade (IC) detector with InAs/Ga(In)Sb type-II superlattice (T2-SL) absorbers is a new type of high-performance infrared photodetector that has many unique features. In this IC detector design, the T2-SL absorber is sliced into multiple thinner segments that are sandwiched between electron and hole barriers, forming one stage. Multiple stages are electrically connected in series. The asymmetric energy-band alignment and ultra-fast carrier transport channel have enabled IC detectors to operate under/near zero-bias. The large lifetime contrast and the great design flexibility make IC detectors very suitable for high temperature operations. Our effort has led to the demonstration of mid-IR single pixel devices operating up to 450 K under zero-bias. These devices achieved superior electrical performance compared to HgCdTe technology at higher operation temperatures. In this presentation, we will discuss the new developments of low-noise mid-IR IC photodetectors and their focal plane arrays. Device studies on the influence of design on their optical and electrical performance will be discussed, and the most recent technical progress is also reported.
The objective of this study is to optimize the absorption in the active region of InAs/GaSb T2SL photodetectors for the
realization of high-performance MWIR devices. Two sets of MWIR (λ100% cut-off ~ 5.5μm at 77K) T2SL detectors were
realized; one set with varied detector absorber thickness, the other set with varied T2SL period. The T2SL material
quality was evaluated on the basis of room temperature photoluminescence (RTPL) and the high-resolution X-ray
diffraction (HRXRD) data. Then the device performance was compared using spectral response, dark current and
responsivity measurements. Finally, quantum efficiency was calculated and employed as a metric for the definition of
the optimal T2SL period and active region thickness. For the first part of the study, a homojunction pin architecture
based on 8 monolayers (MLs) InAs/8MLs GaSb T2SL was used. The thickness of the non-intentionally doped absorber
layers were 1.5μm, 2.5μm, and 3.5μm. For the second part of the study, unipolar barrier (pBiBn) devices were grown.
The thickness of the absorber region and the T2SL constituent InAs layer thicknesses were kept the same (1.5 μm and 8
MLs, respectively) whereas the T2SL constituent GaSb thickness was varied as 6 MLs, 8 MLs, and 10 MLs. We have
found that the pin detector with 2.5 μm thick absorber and the pBiBn detector with 8 ML InAs/ 8 ML GaSb T2SL
composition are, within the scope of this study, optimal for the realization of MWIR single-element devices and FPAs
with corresponding architectures.
There is an increasing interest in the development of high operating temperature (HOT) detectors with InAs/Ga(In)Sb Type-II superlattice (T2-SL) material systems. A wide variety of unipolar barrier structures have been investigated and successfully implemented in low-noise device architectures. In this paper, some of our recent work on the development of HOT mid-IR (MWIR) T2-SL photodetectors with interband cascade schemes will be summarized. In these structures, the discrete InAs/GaSb SL absorbers are sandwiched between quantum-engineered electron and hole barriers, which facilitate photovoltaic operation and efficient photo-carrier extraction. Even at its initial stage of development, such an advanced design has led to the demonstration of mid-IR photodetectors with background-limited operation above 150 K (300 K, 2π field-of-view), as well as above room temperature zero-bias operation. Further understanding of the device operation and design principles will also be discussed.
Over the last several years, owing to the implementation of advanced device architectures, antimony-based type-II
superlattice (T2-SL) infrared (IR) photodetectors and their focal plane arrays (FPAs) have achieved significant
advancements. Here we present our recent effort towards the development of high operating temperature (HOT)
mid-IR (MWIR) photodetectors, which utilizes an interband cascade scheme with discrete InAs/GaSb SL absorbers,
sandwiched between electron and hole barriers. This low-noise device architecture has enabled background-limited
operation above 150 K (300 K, 2π field-of-view), as well as above room temperature response in the mid-IR region.
The detector yields a dark current density of 1.10×10-7 A/cm2 (1.44×10-3 A/cm2) at -5 mV, and a Johnson-limited D*
of 2.22×1011 cmHz1/2/W (1.58×109 cmHz1/2/W) at 150 K (room temperature) and 3.6 μm, respectively. In this
presentation, we will discuss the operation principles of the interband cascade design and our most recent progress
in MWIR photodetectors toward high operating temperatures.
Long-wave infrared (LWIR) detector technologies with the ability to operate at or near room temperature are very
important for many civil and military applications including chemical identification, surveillance, defense and medical
diagnostics. Eliminating the need for cryogenics in a detector system can reduce cost, weight and power consumption;
simplify the detection system design and allow for widespread usage. In recent years, infrared (IR) detectors based on
uni-polar barrier designs have gained interest for their ability to lower dark current and increase a detector's operating
temperature.
Our group is currently investigating nBn and pBp detectors with InAs/GaSb strain layer superlattice (SLS)
absorbers (n) and contacts (n), and AlGaSb and InAs/AlSb superlattice electron and hole barriers (B) respectively. For
the case of the nBn structure, the wide-band-gap barrier material (AlGaSb) exhibits a large conduction band offset and a
small valence band offset with the narrow-band-gap absorber material. For the pBp structure (InAs/AlSb superlattice
barrier), the converse is true with a large valence band offset between the barrier and absorber and a small or zero
conduction band offset. Like the built-in barrier in a p-n junction, the heterojunction barrier blocks the majority carriers
allowing free movement of photogenerated minority carriers. However, the barrier in an nBn or pBp detector, in contrast
with a p-n junction depletion layer, does not contribute to generation-recombination (G-R) current.
In this report we aim to investigate and contrast the performance characteristics of an SLS nBn detector with that of
and SLS pBp detector.
We present our efforts on development of high performance low noise, long-wave infrared (LWIR)
and multicolor detectors based on the InAs/GaSb strained layer material (SLS) material system. The LWIR
SLS detector with PbIbN architecture showed improved performance over the conventional PIN design due to
unipolar current blocking layers. At 77K and Vb=-0.25V, a responsivity of 1.8 A/W, dark current density of
1.2 mA/cm2, quantum efficiency of 23% and shot noise limited detectivity (D*) of 8.7×1010 Jones (λc = 10.8
μm) has been observed. Dual band response was registered with 50% cut-off wavelengths of 5μm and 10μm
from an SLS detector with the pBp design. The responsivity equal to 1.6 A/W (at λ = 5 μm and Vb = +0.4 V)
and 1.8 A/W (at λ = 9 μm and Vb = -0.7 V) for MWIR and LWIR absorbers was achieved with corresponding
values of specific detectivity 5 x 1011 Jones and 2.6 x 1010 Jones, respectively. The maximum values of
quantum efficiency were estimated to 41% (MWIR) and 25% (LWIR) at Vb = +0.4V and Vb = -0.7V.
Moreover, the diffusion-limited behavior of dark current at higher temperatures was observed for the MWIR
absorber for pBp detector. Finally, three-color response was registered from three contact device with nBn
architecture for SWIR and MWIR and heterojunction PIbN architecture for LWIR detection (NbNbiP). At
77K, the cut-off wavelength for SWIR, MWIR and LWIR regions have been observed as 3.0 μm, 4.7 μm, and
10.1 μm respectively. At the same temperature, D* of 1.4 × 1010 Jones, 1.8 × 1010 Jones and 1.5 × 109 Jones
for SWIR, MWIR and LWIR signals has been observed.
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