This PDF file contains the front matter associated with SPIE Proceedings Volume 12687, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The linear-mode, avalanche photodiode array (LmAPD) based on bandgap-engineered HgCdTe, grown by Metal Organic Vapour Phase Epitaxy (MOVPE) is an important product type at Leonardo UK. High-value instruments often employ LmAPDs where the photon count is low and conventional detectors cease to be sensitive. Applications now split into three main categories. Firstly, for applications with intrinsically short integration time, such as: wavefront sensors, fringe trackers and devices for rapid-time-domain astronomy, LmAPDs arrays are established in 320x256 and 515x512 formats, with an avalanche gain of >100x at 15V bias and 80-100K operating temperature. Secondly, for free-space telecoms, LIDAR and gated arrays a GHz version of the LmAPD is available. Thirdly, there is a class of applications with very low photon arrival rates and these provide the most demanding of challenges for LmAPDs. The main field is astronomical imaging and interferometry. In a collaboration with the University of Hawaii (UH) a 1kx1k/15μm device been developed and together with a low dark current version of the LmAPD is under detailed characterisation at UH. Initial results show dark currents below 0.001ph/s/pixel and usable avalanche gain up to 10x. A 2kx2k/15μm format device funded by ESA is currently in trial manufacture. This paper provides an update on the technology and the status of our developments and collaborations.

Superconducting nanowire single photon detectors (SNSPDs) have low dark counts, improved gain stability, and high resolution compared to traditional infrared detectors. Recent work at National Institute of Standards and Technology (NIST) and National Aeronautics and Space Administration (NASA) has incorporated SNSPDs into arrays and extended the response into the mid-infrared to use for spectroscopy and hyperspectral imaging. We are developing novel methods to spectrally calibrate and measure stability of these detectors in this challenging wavelength range from 3 μm to 25 μm. We present our design of a novel cryogenic apparatus uniquely focused on making quantitative efficiency measurements of these quantum detectors by directly comparing to a reference calibrated blocked-impurity-band (BIB) detector so they can be used by researchers from federal agencies, universities, and industry.

A means of enhancing transmission to enable higher efficiency detector and imaging array performance from ultraviolet (UV) to infrared (IR) bands involves deposition of novel nanostructured optical layers with tunable refractive index properties. This nanostructured antireflection (AR) coating technology provides broadband and omnidirectional suppression of light reflection/scattering to substantially increase transmission. The multilayer AR coatings can be furthermore custom-designed for operation over specific wavebands for a wide range of potential optical applications, particularly for maximizing electro-optic and IR radiation transmission onto the surfaces of detector arrays to greatly enhance sensitivity and efficiency over mid-wave infrared (MWIR) and long-wave infrared (LWIR) bands of detection. Advanced AR nanostructured coatings have been fabricated using a novel growth process and developed for high AR performance, on substrates including GaSb and Si, as well as on GaSb-based focal plane array (FPA) devices, for IR band sensing applications. These nanostructured coatings further minimize reflection losses to provide substantial improvements in increased transmission over thin film AR coating technologies such as quarter wavelength stacks, further enabling higher quantum efficiency and broadband detection of MWIR and LWIR band radiation from the AR-coated optical sensing and FPA imaging devices. Here we review recent developments of this high-performance nanostructured AR coating technology for advancing NASA Earth Science sensing and imaging applications.

The PRobe far Infrared Mission for Astrophysics (PRIMA) is a mission concept for a NASA cryogenic observatory in an Earth-Sun L2 halo orbit, designed to reveal how abundant elements are built up in galaxies over cosmic time. To achieve the target sensitivity in the wavelength range of 25 to at least 200 microns, its wideband spectrometer and multiband spectrophotometric imager/polarimeter need to operate at 0.1 K, and its primary mirror and relay optics need to be at 4.5 K. To meet these cooling needs, the PRIMA study team is designing a cryogen-free cooling system with a combination of passive radiators and thermal shields, a hybrid mechanical cooler and a continuous Adiabatic Demagnetization Refrigerator system. The PRIMA mechanical cooler is slightly modified JWST Mid-Infrared Instrument (MIRI) cooler that uses ³He as the working fluid in its JT stage. This paper first discusses the overall thermal requirements and the system's thermal architecture and then describes the main thermal subsystems in the cryocooling chain. Finally, the paper presents compressor and ³He Joule-Thomson (JT) effect test results to validate the predicted performance of PRIMA’s 4.5 K mechanical cryocooler.

Leonardo are currently involved in a number of projects within the space and astronomy sector for MCT cryogenically cooled detectors and DLATGS pyroelectric products. Leonardo MCT avalanche photodiodes have had significant success for both imaging and wavefront sensing applications, demonstrating sub photon sensitivity in the short wave. The latest results on the development of arrays in a number of configurations for a range of products are presented. We report on the progress of our latest COTS MCT IDCA flight programme following BIRD. Data is also presented on Leonardo’s current work in extending MCT into the visible band and creating high speed devices suitable for GHz, deep space communication.

We demonstrate the metamorphic growth of InAs_1-xSb_x (x = 0.08 – 0.68) layers on GaAs substrate with an optimized InAs-based intermediate buffer layer by molecular beam epitaxy. The broad range of group-V flux ratio is applied to investigate the effect between Sb incorporation and material quality. We find that high Sb compositions significantly roughen surface morphology, and that optimized growth temperature is crucial to prevent phase separation and surface segregation of Sb atoms. In addition, we achieve a high degree of strain relaxation (~94%) in the metamorphic InAsSb layers even with a 58% Sb composition. This result indicates that our InAs/GaAs virtual substrate is suitable for the growth of an almost fully relaxed InAsSb layer. Also, we investigate a threading dislocation density (TDD) trend with the broad range of Sb compositions, and a drastically increasing TDD trend (> 200 times) was observed. Finally, we report a narrow bandgap of 0.13 eV at 10 K of the InAs_0.42Sb_0.58 layer, which is promising for the detection of longwavelength infrared radiation. This InAsSb layer on GaAs substrate opens up possibility for mid-wavelength and long-wavelength infrared optoelectronics applications.

We present a near-infrared (NIR) imager based on high-performance organic photodiode in terms of dark current, specific detectivity and response time. A carefully designed interfacial layer is introduced in the thin-film organic photodiode stack to reduce trap assisted carrier emission leading to sub-nA/cm² dark current and external quantum efficiency above 50% in the NIR range. The developed imager chip benefits from this improved dark current-voltage characteristic (high light signal to dark noise ratio) and enables high-resolution, monolithic NIR image sensors.

We report the useful approach toward the practical imaging solution for long-wavelength infrared (LWIR). In order to make use of the LWIR sensors conveniently in everyday life, the imaging module needs to be slim and small so that it can be mounted inside end-user devices without big difficulties. At the same time, the image qualities should have a sufficient level to guarantee that people can easily identify object shapes and recognize temperature differences when they see the resultant images. In this paper, we focus on those two crucial points for the practical LWIR imaging device. First, to make the compact optical system, we adopted a thin meta-surface lens of a focal length 2 mm which is showing the effective total top length (TTL) less than 3 mm. Second, to enhance the image sharpness degraded relatively due to the lens, the deep learning method of the U-net model is introduced. The patterns of the USAF resolution target chart indicate the increase of modulation value by 3~8 times after applying the learning process. We believe that our work helps to expand the pragmatic application area of the LWIR imaging sensors in the near future.

The development of a scalable, low cost, low power, and room temperature operating detector technology capable of high spatial resolution imaging over IR bands of interest can advance and extend space and satellite sensing capabilities such as remote sensing and earth observation. Conventional infrared (IR) band photodetectors based on HgCdTe material operating over short-wave infrared (SWIR), mid-wave infrared (MWIR), and/or long-wave infrared (LWIR) bands often require external cooling to achieve high performance IR sensing and imaging. By integrating bilayers of doped graphene to function as a high mobility channel to aid the recombination of photogenerated carriers, a graphene-enhanced IR photodetector with HgCdTe absorbing layer can be developed providing high performance uncooled detection over SWIR, MWIR, and LWIR (~1.3-14 μm) bands. Development of the high-performance IR photodetector technology involves ptype doping of graphene bilayers deposited on Si/SiO₂ with boron using a spin-on dopant (SOD) process, and then transfer of the doped bilayer graphene onto HgCdTe substrates. The graphene-enhanced HgCdTe SWIR/MWIR/LWIR band detectors were analyzed and characterized material and optoelectronically to demonstrate high performance IR detection at room temperature for advanced NASA Earth Science, defense, and commercial applications.

Artificial Intelligence-based object recognition in the infrared spectrum region is essential for autonomous applications and will likely require on-demand spectral tuning of an imaging sensor. Here we develop a quantum well infrared photodetector (QWIP) with an asymmetrically doped double quantum well (QW) array which provides the means to control its spectral sensitivity with an applied bias. The test structures were designed using a Schrödinger-Poisson solver to find the electronic transition energies for symmetric and antisymmetric double-QW states. The design, growth, and characterization of QWIPs have been performed aiming at the 5-8 μm and 8-12 μm detection wavelengths. The structures were grown by molecular beam epitaxy and contained 25 periods of coupled double GaAs QWs and Al_xGa_1-xAs barriers. One of the QWs in the pair was doped to provide potential asymmetry allowing for control of the electron population on the split levels by the bias applied to the QWIP. The QW structures were calibrated using TEM, and tested with blackbody radiation and FTIR down to 77 K. As a result, the ratio of the responsivities of the two bands at about 8 and 11 μm as well as 5 and 8 μm was controlled with up to an order of magnitude by the applied bias within +/- 4V.

Geiger mode avalanche photodiodes (GmAPDs) are a core component in optical communications, quantum computing, and lidar applications. However, for space-based applications, indium phosphide (InP) based APDs operating in the infrared (IR) suffer from accelerated radiation-induced performance degradation. Specifically, displacement damage induces defects in the APD material which deteriorate the electrical performance of the device (increased dark count rate (DCR)), limiting operability and lifetime. The amount of APD radiation damage scales with the volume of the avalanche region. The current approach to reducing the displacement damage in APD architectures is to shrink the entire APD diameter. However, this technique also shrinks the photo-active volume of the device, which imposes additional challenges for light absorption. In this paper, we examine candidate architectures to shrink the volume of the avalanche region while maintaining the absorber region. Using ATHENA and ATLAS software packages in Silvaco, we investigate several designs with varying sidewall etch profiles. We examine the change in electric field distribution and probability of avalanche, using these results to select candidate architectures for radiation-hardened APDs.

Mercury cadmium telluride (HgCdTe or MCT) is the material of choice for infrared avalanche photodetectors (APDs) owing to its desirable qualities including high quantum efficiency and low excess noise factor. Recent advancements in growth techniques have allowed for bandgap engineered MCT films that further enhance the performance of MCT APDs. Monte Carlo has been a widely used method for simulating the multiplication process within avalanche photodiodes (APDs) due to its ability to accurately simulate non-equilibrium transport. In this work, we demonstrate how the gain, excess noise, and bandwidth of bandgap engineered MCT APDs can be accurately modeled in 3-D using Monte Carlo.

We present a numerical simulation study at 200K of pBn and nBn Hg_1−xCd_xTe barrier detectors, focused on the effects of the composition profile on the J-V characteristics in dark. Considering a conventional barrier detector structure with three regions (absorber, barrier, cap), we discuss how the J-V characteristics are affected by the steepness of the cap/barrier and barrier/absorber interfaces, especially in the nBn configuration.

Type-II strained-layer superlattices have theoretically predicted advantages that make them an attractive material system for use in infrared technology. However, the influence of structural disorder has been demonstrated to negatively impact the performance of these materials. A recent development in infrared technology is the use of curved focal-plane arrays which promise improved uniformity of sensitivity and a reduction in the optical complexity of the device. Curving of the wafer introduces mechanical strain into the absorber layer which can also impact the vertical carrier mobility. This work reports on an analysis of the influence of external strain and disorder on the vertical hole mobility in curved focal-plane arrays utilizing a mid-wave InAs/GaSb absorber layers. A series of quantum transport calculations is performed over a range of strain configurations for two different structures: an ideal superlattice and a superlattice with graded interfaces and disorder. Finally, the impact these effects have on the quantum efficiency of a hypothetical curved-FPA is approximated, and a potential avenue for improved device design is suggested.

To test whether conventional infrared materials can be used to control the electronic wavefunction to form a topological state, a 6.2 Å metamorphic (InAs/InGaSb/InAs) quantum well (QW) absorber with ~60 meV of hybridization gap (Δ) was investigated. We developed a thick metamorphic InGaSb buffer layer on GaAs wafer to create a 6.2 Å lattice constant for the QW growths. The lattice constant of virtual substrates (VSs) was very close to the target value of 6.2 Å, however the resulting crystalline quality of the VSs was inefficient for topological insulator. The cross-sectional transmission electron microscopy image revealed that the dislocation density in the InGaSb buffer layer was high closer to the GaAs substrate and gradually reduced upon continued growth. However some mismatch-related defects were propagated into the absorber region, consequently degraded the transport quality of absorber. The QW absorber grown on VS had a low mobility. The mobility was dramatically improved by selecting pseudomorphic QW or superlattice absorber with a small Δ that was grown on a lattice-matched GaSb substrate. Hence, in order for the proposed 6.2 Å materials to be viable for sensing applications, a critical effort will be the development of better optimized metamorphic buffers for the design or of highlyhybridized psedomorphic designs that can be grown on lattice-matched substrates.

This article proposes a plasmonic resonance-based optical nanoantennas geometry, called multipolarized, for the use of infrared sensors on focal plane array (FPA) substrates. The fabricated nanoantennas with electronbeam lithography and their determined resonance frequency through infrared spectroscopy and finite element simulation are the results presented in this work. We present a strategy for designing and fabricating nanoantennas with high performance and sensitivity for infrared sensors. The proposed multipolarized nanoantenna geometry can be used in plan array sensors for thermal imaging detection, providing high performance and sensitivity in the infrared range.

The aim of this work is the characterization of a Shack-Hartmann wavefront sensor prototype through a statistical analysis in accordance with the official Mexican standard. To determine the repeatability and reproducibility of ophthalmic aberration measurements, given in Zernike polynomials, a measurement protocol was proposed. The measurements were obtained using an experimental optical system, which uses a super luminescent diode (SLD) IR, as well as ophthalmic trial lenses to introduce optical aberrations, which are used as reference materials. The complete optical system is intended to be used as an experimental aberrometer to obtain low order aberrations of the human eye in vivo.

Conventional InAs/GaAs QD heterostructures are drawing the significant amount of interest among the worldwide researchers due to the excellent carrier confinement, high optical absorption, lower binding energy and high electron mobility. Also, impact of Sb incorporation in the capping layers provides the far-infrared wavelength emission window (1.3 μm to 1.56 μm). In current work, the effects of strain and composition on the optical properties of vertically uncoupled InAs/InGaAs quantum dots (QDs) capped with a thin layer combining Sb quaternary alloys are investigated experimentally. In this work, growth rate of the QDs formation is varied such as 0.05 ML/s, 0.07 ML/s and 0.1 ML/s for selective 28% Sb composition. The atomic force microscopic (AFM) measurement is performed on the grown quaternary capped QDs heterostructures and better dot uniformity and density is observed for selective growth rate sample. The out-plane X-ray diffraction (XRD) is measured for all the growth rate varying heterostructures. The strains are estimated from the corresponding XRD plots and such results confirm the defect free growth of heterostructures with reduced strain and high dot size for 0.05 ML/s growth rate sample. The photoluminescence (PL) is conducted to characterize the optical properties of the grown QDs heterostructures. The 20 K PL peak is gradually shifted from 1214 nm to1249 nm with the decreasing growth rate from 0.1 ML/s to 0.05 ML/s. Therefore, growth rate is optimized for InAs/InGaAsSb QD heterostructures, which will be exhibited the higher photo absorption and carrier lifetime and such heterostructures can be a promising candidate for III-V QD based opto-electronic devices.

The current work represents the influence of Sb composition on strain profiles, band alignment of InAs/GaAsSb Stranski-Krastanov (SK) quantum dots (QD) heterostructure. A single layer InAs/GaAs SK QD heterostructure has been utilised as a reference structure (sample A). Three different structures B, C and D are chosen with the Sb composition of 10%, 14% and 22% in the capping layer on the InAs QDs. The strain distribution of InAs quantum dots with GaAs1-xSbx capping has been investigated in detail by using Nextnano simulation software. The transition from type-I to type-II band alignment occurs after 14% Sb incorporation. The effect of variation in the Sb component on the strain profile is analysed in terms of hydrostatic and biaxial strain. In the strain profiles, the biaxial strain increases significantly from samples A to D, whereas the hydrostatic strain is reducing from samples A to D inside the QD region simultaneously. Further, low temperature photoluminescence (PL) has been performed to validate the simulated results. The PL peak is originated at ~1030 nm for sample A, which shows a good agreement with the simulated value ~1071 nm. With the similar dot size, the simulated PL peaks are found at 1116, 1284, 1675 nm for samples B, C and D, respectively. A slight variation is observed in the experimentally obtained PL peaks and simulated one due to the incorporation of higher Sb content. With the higher Sb content, relatively more defects are generated, which affects the experimental PL peaks. Also, a red shift is found in the PL peaks from ~1030 nm to ~1213 nm at 19K and it gives an insight to develop various optoelectronic devices using such QDs heterostructure.

A Schottky infrared photodetector with dual mechanisms, where both photoelectric and photothermal current generation mechanisms coexist is presented. The dominant role of these mechanisms changes with surface passivation process. In the device without passivation process, the device exhibits high responsivity due to the presence of the photothermal effect but has slow rise and recovery times. However, after surface passivation treatment, the device characteristics are dominated by the photoelectric effect, showing a significantly faster response time, capable of detecting signal level changes within less than 80 ms, with a constant current difference between on and off states. This unique multifunctionality promotes the development of Schottky device capable of achieving multiple optical detection purposes