There has been a tremendous amount of research on two dimensional materials (2DMs) in recent years, suggesting their unique properties for optoelectronic devices. While a good momentum on implementing 2DMs for photodetection for visible and infrared (IR) photon detection exists, progress on demonstration of imaging systems based on these material have been slow. Most of reported studies have been based on single-pixel devices, which is unable to compete with the quantity and quality of information provided by massively parallelized mega-pixel imagers based on complementary metal-oxide semiconductor (CMOS) readout electronics. In this paper, we explore opportunities for achieving reliable and high-resolution FPA cameras using 2DMs. We will cover most relevant new materials in the field and cover photodetection methods. Our goal is to address the opportunities and challenges of using 2DMs for future imaging systems and their integration with CMOS electronics in a condensed form.
A recently, triple-band shortwave infrared-mid-wave infrared-long-wave infrared (SWIR-MWIR-LWIR) photodetector based on III-V material showed promising performance with successful separation of operation regimes. When the applied bias voltage changes, the device demonstrates consecutively the three different colors detection, corresponding to the different bandgaps of SWIR, MWIR and LWIR absorber regions. Nevertheless, the bias dependency for MWIR and especially for LWIR signals is still much of concern. The triple-band device reveals strong bias dependency for quantum efficiency (QE) for MWIR and LWIR response as well as high dark current value, which made the structure unsuitable for FPA imaging application. In this matter, to control the high bias dependency and dark current value observed in previous design, a new approach was chosen in design to enhance the performance of the triple-band device.
For the current strained layer superlattice (SLS) based FPAs mesa structures are used to define the pixels. For those SLS based FPAs with scaled pixel size making the mesa structures is challenging due to the need for deep etch, and then passivation process. One of the possible solutions to address this issue is to consider a planar structure and avoiding the mesa-isolation etching or complex surface treatment/ passivation process. In this work, the recent progress on planar SLS photodetector using ion-implantation for device isolation is presented. In this method of fabrication, ion implantation was applied from the top to bombardment the surface for device isolation, similar to mesa-isolation step in device fabrication. The devices are presented here are heterostructure SLS photodetector. The electrical and optical performance of the devices were characterized to give deeper view of the device performance.
A two terminal short wavelength infrared heterojunction phototransistors based on type-II InAs/AlSb/GaSb on GaSb substrate are designed fabricated and presented. With the base thickness of 40 nm, the device exhibited 100% cut-off wavelengths of ~2.3 μm at 300K. The saturated peak responsivity value is of 325.5 A/W at 300K, under front-side illumination without any anti-reflection coating. A saturated optical gain at 300K was 215 a saturated dark current shot noise limited specific detectivity of 4.9×1011 cm·Hz1/2/W at 300 K was measured. Similar heterojunction phototransistor structure was grown and fabricated with different method of processing for high speed testing. For 80μm diameter circular diode size under 20 V applied reverse bias, a -3 dB cut-off frequency of 1.0 GHz was achieved, which showed the potential of type-II superlattice based heterojunction phototransistors to be used for high speed detection.
Third generation of infrared imagers demand performances for higher detectivity, higher operating temperature, higher resolution, and multi-color detection all accomplished with better yield and lower manufacturing costs. Antimonide-based gap-engineered Type-II superlattices (T2SLs) material system is considered as a potential alternative for Mercury- Cadmium-Telluride (HgCdTe) technology in all different infrared detection regimes from short to very long wavelengths for the third generation of infrared imagers. This is due to the incredible growth in the understanding of its material properties and improvement of device processing which leads to design and fabrication of better devices. We will present the most recent research results on Antimonide-based gap-engineered Type-II superlattices, such as high-performance dual-band SWIR/MWIR photo-detectors and focal plane arrays for different infrared regimes, toward the third generation of infrared imaging systems at the Center for Quantum Devices. Comparing metal-organic chemical vapor deposition (MOCVD), vs molecular beam epitaxy (MBE).
Most of reported HPTs in literatures are based on InGaAs compounds that cover NIR spectral region. However, InGaAs compounds provide limited cut-off wavelength tunability. In contrast, type-II superlattices (T2SLs) are a developing new material system with intrinsic advantages such as great flexibility in bandgap engineering, low growth and manufacturing cost, high-uniformity, auger recombination suppression, and high carrier effective mass that are becoming an attractive candidate for infrared detection and imaging from short-wavelength infrared to very long wavelength infrared regime. We present the recent advancements in T2SL-based heterojunction phototransistors in e– SWIR, MWIR and LWIR spectral ranges. A mid-wavelength infrared heterojunction phototransistor based on type-II InAs/AlSb/GaSb superlattices on GaSb substrate has been demonstrated. Then, we present the effect of vertical scaling on the optical and electrical performance of heterojunction phototransistors, where the performance of devices with different base width was compared as the base was scaled from 60 down to 40 nm.
InAs/InAs1-xSbx/AlAs1-xSbx type-II superlattices (T2SLs) is a system of multi-interacting quantum wells. Since its introduction, this material system has drawn a lot of attention especially for infrared detection. In recent years, InAs/InAs1- xSbx/AlAs1-xSbx T2SL material system has experienced incredible improvements in material quality, device structure designs and device fabrication process which elevated the performances of T2SL-based photodetectors to a comparable level to the state-of-the-art material systems for infrared detection such as Mercury Cadmium Telluride (MCT). In this paper, we will present the current status of InAs/InAs1-xSbx/AlAs1-xSbx T2SL-based photodetectors for detection in different infrared regions, from short-wavelength (SWIR) to long-wavelength (LWIR) infrared, and the future outlook of this material system.
We present a high-performance short-wavelength infrared n-i-p photodiode, whose structure is based on type-II
superlattices with InAs/InAs1-xSbx/AlAs1-xSbx on GaSb substrate. At room temperature (300K) with front-side
illumination, the device shows the peak responsivity of 0.47 A/W at 1.6mm, corresponding to 37% quantum efficiency at
zero bias. At 300K, the device has a 50% cut-off wavelength of ~1.8mm. For −50mV applied bias at 300 K the
photodetector has dark current density of 9.6x10-5 A/cm2 and RxA of 285 Ω•cm2, and it revealed a detectivity of
6.45x1010 cm•Hz1/2/W. Dark current density reached to 1.3x10-8 A/cm2 at 200 K, with 36% quantum efficiency which
leads to the detectivity value of 5.66x1012 cm•Hz1/2/W.
We report InAs/InAs1-xSbx type-II superlattice base photodetector as high performance long-wavelength infrared nBn device grown on GaSb substrate. The device has 6 μm-thick absorption region, and shows optical performance with a peak responsivity of 4.47 A/W at 7.9 μm, which is corresponding to the quantum efficiency of 54% at a bias voltage of negative 90 mV, where no anti-reflection coating was used for front-side illumination. At 77K, the photodetector’s 50% cut-off wavelength was ~10 μm. The device shows the detectivity of 2.8x1011 cm.√Hz/W at 77 K, where RxA and dark current density were 119 Ω•cm2 and 4.4x10-4 A/cm2 , respectively, under -90 mV applied bias voltage.
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