Singer M.,Semiconductor Devices |
Oster D.,Israeli Ministry of Defense
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010
Cryogenically cooled IR detectors, which are used in applications such as situational awareness, search & track, missile launch and approach warning, typically use wide angle, single field of view optical systems. We describe a complete IR imaging optical assembly for such applications, which is mounted inside a cold shield and is maintained at a stabilized cryogenic temperature inside the dewar. A typical system houses two to four lenses and a cold filter, and weighs 5 grams or less. Despite this integration and added complexity, the resulting Detector-Dewar-Cooler Assembly (DDCA) has overall dimensions similar to those of equivalent-performing DDCAs without integrated optics. Moreover, Compact designs integrating wide-angle optics and a warm, high-magnification, telescope module for narrow FOV applications are seen as a straightforward extension of our system. We conclude with an in-depth, technical overview describing the design considerations for a typical wide-field imaging system. © 2010 Copyright SPIE - The International Society for Optical Engineering.
Klipstein P.C.,Semiconductor Devices
Physical Review B - Condensed Matter and Materials Physics | Year: 2015
A solution of the k·p model is presented for bulk and quantum spin hall (QSH) edge states in semiconductor topological insulator (TI) quantum wells (QWs), bounded at the edge by an infinite wall potential. The edge states are exponentially localized, with a nonzero amplitude at the QW edge, and obey standard boundary conditions for the wave function and its derivative. Single helical edge states with spin locked to the direction of motion are found in the TI band gap (ETI) of QWs with both strong (HgTe/CdTe) and weak (InAs/GaSb/AlSb) s-p hybridization, but in the second case only below a small critical band gap, Ecrit∼1.6meV. For ETI>Ecrit, there appear to be two degenerate states for each spin direction. It is suggested that Z2-like topological properties can still be maintained if one of these states is spurious or suppressed by disorder. The effect of interface band mixing, and band mixing due to structural inversion asymmetry and bulk inversion asymmetry is also considered. Simple model Hamiltonians are developed for the bulk and edge states which are calibrated against a bulk eight-band k·p calculation close to the TI transition. At the transition, the zero gap bulk states exhibit a spin splitting, essentially changing the Dirac point to a circle. In the TI phase, there is a small change in the dispersion of the QSH edge states. These results confirm the robustness of the QSH edge states to spatial symmetry breaking interactions. © 2015 American Physical Society.
Klipstein P.C.,Semiconductor Devices
Journal of Crystal Growth | Year: 2015
XBn n and XBp p barrier detectors grown from III-V materials on GaSb substrates have recently been shown to exhibit a low diffusion limited dark current and a high quantum efficiency. Two important examples are InAsSb/AlSbAs based XBn n devices with a cut-off wavelength of λ C~4.1μm, and InAs/GaSb Type II superlattice (T2SL) based XBp p devices, with λ C~9.5μm. The former exhibit background limited performance (BLIP) at F/3 up to ~175K, which is a much higher temperature than observed in standard generation-recombination limited devices, such as InSb photodiodes operating in the same Mid Wave IR atmospheric window. The Long Wave IR (LWIR) T2SL XBp p device has a BLIP temperature of ~100K at F/2. Using the k · p and optical transfer matrix methods, full spectral response curves of both detectors can be predicted from a basic knowledge of the layer thicknesses and doping. The spectral response curves of LWIR gallium free InAs/InAs1-xSbx barrier devices have also been simulated. These devices appear to have a lower quantum efficiency than the equivalent InAs/GaSb XBp p devices. © 2015 Elsevier B.V.
Klipstein P.C.,Semiconductor Devices
Physical Review B - Condensed Matter and Materials Physics | Year: 2010
A Kane-like envelope function Hamiltonian is derived for the Γ15 valence and Γ1 conduction states of lattice-matched, semiconductor superlattice structures, with metallurgically abrupt interfaces. The local microscopic potential is treated as a weak perturbation on that of a reference crystal and is expressed in terms of a one-dimensional profile function, G (z), which modulates the difference between the potentials of the well and barrier materials. In contrast to many previous treatments, all terms up to order "=2 in δ V̄ ( k̄ a )" are included, where δ V̄ is the typical band offset, k̄ is the average momentum modulus of the envelope function, and a is the bulk lattice parameter. Far from the interfaces, the Hamiltonian is identical to the familiar bulk Kane Hamiltonian, with the standard bulk parameters. However, the operator ordering in the valence band is revised from the commonly used Burt scheme. An operator ordering scheme has also been derived for the linear- k P terms that couple conduction and valence states. Expressions have been derived for the δ functionlike, and derivative of a δ functionlike, interface terms. These are off-diagonal and diagonal, respectively, in common atom superlattices like GaAs/ Alx Ga1-x As, where the antisymmetric contribution to G ′ (z) is expected to be small. For superlattices with no common atom, additional interface terms are introduced. If the difference in the spin-orbit splitting energy for the two superlattice materials is comparable with the valence-band offset, then relativistic corrections can introduce many more, weak interface contributions. Part of the relativistic interface matrix has been derived, which includes the most significant terms. Finally, a scheme is proposed for reducing the number of independent Luttinger parameters required, when using the Hamiltonian to fit experimental spectral data. © 2010 The American Physical Society.
Klipstein P.,Semiconductor Devices
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015
SCD has developed a range of advanced infrared detectors based on III-V semiconductor heterostructures, grown on GaSb. The XBn/XBp family of detectors enables diffusion limited behavior with dark currents comparable with MCT Rule-07 and with high quantum efficiencies. InAsSb/AlSbAs based XBn focal plane array detectors with a cut-off wavelength of ∼ 4.1 μm and formats presently up to 1024×1280 / 15 μm, operate with background limited performance up to ∼175 K at F/3. They have a sensitivity and image quality comparable with those of standard InSb detectors working at 77K. In an XBp configuration, the same concept has been applied to an InAs/GaSb type II superlattice (T2SL) detector with a cut-off wavelength of ∼ 9.5 μm, which operates with background limited performance up to ∼100 K at F/2. In order to design our detectors effectively, a suite of simulation algorithms was developed based on the k<. p and optical transfer matrix methods. In a given T2SL detector, the complete spectral response curve can be predicted essentially from a knowledge of the InAs and GaSb layer widths in a single period of the superlattice. Gallium free T2SL detectors in which the GaSb layer is replaced with InAs1-xSbx (x ∼ 0.15-0.5) have also been simulated and the predicted spectral response compared for the two detector types. © 2015 SPIE.