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We examine zero-magnetic-field spin-dependent transmission in nonmagnetic semiconductor heterostructures with structural inversion asymmetry (SIA) and bulk inversion asymmetry (BIA), and report spin devices concepts that exploit their properties. Our modeling results show that several design strategies could be used to achieve high spin filtering efficiencies. The current spin polarization of these devices is electrically controllable, and potentially amenable to high-speed spin modulation, and could be integrated in optoelectronic devices for added functionality.

In photonic or electronic and sonic band structure calculations, one often needs to solve the same eigenvalue problem many times for different sets of parameters. Often only a relatively small part of the matrix varies with these parameter changes. We have recently developed a method where, after the eigenvalue problem is solved once, the remaining cases could be computed much faster (150 times in a typical calculation). Prototype calculations using 2D photonic band structures as examples have verified this concept.

InAs quantum dots formed by submonolayer insertion of InAs into the GaAs quantum well of a GaAs/AlAs double barrier resonant tunnelling structure were studied. A series of sharp resonant tunnelling peaks in I–V characteristics of resonant tunnelling diodes with InAs insertions were observed. Temperature and magnetic field dependent I–V studies and theoretical modeling led us to conclude that these peaks are the result of resonant tunnelling through localized states associated with InAs quantum dots.

The nBn or XBn barrier infrared detector has the advantage of reduced dark current resulting from suppressed Shockley-Read-Hall (SRH) recombination and surface leakage. High performance detectors and focal plane arrays (FPAs) based on InAsSb absorber lattice matched to GaSb substrate, with a matching AlAsSb unipolar electron barrier, have been demonstrated. The band gap of lattice-matched InAsSb yields a detector cutoff wavelength of approximately 4.2 μm when operating at ~150K. We report results on extending the cutoff wavelength of midwave barrier infrared detectors by incorporating self-assembled InSb quantum dots into the active area of the detector. Using this approach, we were able to extend the detector cutoff wavelength to ~6 μm, allowing the coverage of the full midwave infrared (MWIR) transmission window. The quantum dot barrier infrared detector (QD-BIRD) shows infrared response at temperatures up to 225 K.

We report our recent efforts on advancing of antimonide superlattice based infrared photodetectors and demonstration of focal plane arrays based on a complementary barrier infrared detector (CBIRD) design. By optimizing design and growth condition we succeeded to reduce the operational bias of CBIRD single pixel detector without increase of dark current or degradation of quantum efficiency. We demonstrated a 1024x1024 pixel long-waveleng thinfrared focal plane array utilizing CBIRD design. An 11.5 micrometer cutoff focal plane without anti-reflection coating has yielded noise equivalent differential temperature of 53 mK at operating temperature of 80 K, with 300 K background and cold-stop. Imaging results from a recent 10 micrometer cutoff focal plane array are also presented. These results advance state-of-the art of superlattice detectors and demonstrated advantages of CBIRD architecture for realization of FPA.

Publisher Summary Intrinsic infrared detectors in the mid-wavelength and long-wavelength ranges are based on interband transition, which promotes an electron across the band gap (Eg) from the valence band to the conduction band. This chapter describes the use of multi-quantum-wells (MQWs)-based intersubband transition for infrared detection. The spectral response of the detectors can be tuned by controlling the Eg of the photosensitive material. The MQW structures to detect infrared radiation can be explained by using the basic principles of quantum mechanics. The quantum well is equivalent to the well-known “particle in a box” problem in quantum mechanics, which can be solved by the time-independent Schrodinger equation. The solutions to this problem are the Eigen values that describe energy levels inside the quantum well in which the particle is allowed to exist. The positions of the energy levels are primarily determined by the quantum-well dimensions. The quantum-well infrared photodetectors (QWIPs) discussed in the chapter use the photo-excitation of the electron between the ground state and the first excited state in the conduction band (valance band) quantum well. The quantum-well structure is designed so that these photoexcited carriers can escape from the quantum well and get collected as photocurrent.

Publisher Summary This chapter provides an overview of type-II superlattice infrared detectors. The type-II InAs/GaSb superlattices have several fundamental properties that make them suitable for infrared detection: (1) their band gaps can be made arbitrarily small by design, (2) they are more immune to band-to-band tunneling compared with bulk material, (3) the judicious use of strain in type-II InAs/GaInSb strained layer superlattice (SLS) can enhance its absorption strength over that of the type-II InAs/GaSb superlattice to a level comparable with HgVdTe (MCT), and (4) type-II InAs/Ga(In)Sb superlattices also reduce Auger recombination. In addition, the dark current characteristics of type-II superlattice-based single element long-wavelength infrared (LWIR) detectors are currently approaching state-of-the-art MCT detector. Noise measurements highlight the need for surface leakage suppression, which can be tackled by improved etching, passivation, and device design. The chapter also describes the principles behind advanced superlattice infrared detectors based on heterostructure designs. It also explores some aspects of device fabrication and characterization.

Unipolar barriers can block one carrier type but allow the un-impeded flow of the other. They can be used to implement the barrier infra-red detector (BIRD) design for increasing the collection efficiency of photo-generated carriers, and reducing dark current generation without impeding photocurrent flow. In particular, the InAs/GaSb/AlSb material system, which can be epitaxially grown on GaSb or InAs substrates, is well suited for implementing BIRD structures, as there is considerable flexibility in forming a variety of alloys and superlattices, and tailoring band offsets. We describe our efforts to achieve high-performance long wavelength InAs/GaSb superlattice infrared photodetectors based on the BIRD architecture. Specifically, we report a 10 μm cutoff device based on a complementary barrier infrared detector (CBIRD) design. The detector, without anti-reflection coating, exhibits a responsivity of 1.5 A/W and a dark current density of 1×10-5 A/cm2 at 77K under 0.2 V bias. It reaches 300 K background limited infrared photodetection (BLIP) operation at 101 K, with a black-body BLIP D* value of 2.6×1010 cm-Hz1/2/W for 2π field of view under 0.2 V bias.

Mid-wave infrared (MWIR) and long-wave infrared (LWIR) multicolor focal plane array (FPA) cameras are essential for many DoD and NASA applications including Earth and planetary remote sensing. In this paper we summarize our recent development of large format multicolor QWIP FPA that cover MWIR and LWIR bands.

We describe a long wavelength infrared detector where an InAs/GaSb superlattice absorber is surrounded by a pair of electron-blocking and hole-blocking unipolar barriers. A 9.9 μm cutoff device without antireflection coating based on this complementary barrier infrared detector design exhibits a responsivity of 1.5 A/W and a dark current density of 0.99×10−5 A/cm2 at 77 K under 0.2 V bias. The detector reaches 300 K background limited infrared photodetection (BLIP) operation at 87 K, with a black-body BLIP D∗ value of 1.1×1011 cm Hz1/2/W for f/2 optics under 0.2 V bias.