D. T. Cheung

Characterization of Te precipitates in CdTe crystals

Te precipitates in CdTe have been characterized by Auger spectroscopy, x‐ray diffraction, and Raman spectroscopy. The x‐ray results show that the precipitated Te in Bridgman‐grown CeTe crystals has the same structural phase as observed in elemental Te under high pressure. Auger and Raman microprobe spectroscopy were carried out to confirm Te precipitates in CdTe and identify the symmetry of the Te precipitates.

Infrared focal planes in intrinsic semiconductors

In this paper, we review the state-of-the-art of intrinsic semiconductor detector arrays and project future areas of development. Infrared focal planes in intrinsic semiconductors offer advantages over extrinsic semiconductor structures in both operating temperature and quantum efficiency. Although the device function of spectral filtering and detection of the incident photon flux is now well understood in intrinsic semiconductors, the function of signal processing has only recently been investigated. As a result, research is directed toward implementation of both hybrid devices, in which the signal processing is accomplished in a silicon multiplexer which is physically and electrically interfaced with an intrinsic semiconductor detector array, and monolithic charge transfer devices in which detection and signal processing are accomplished in the same semiconductor. In the monolithic approach, charge transfer devices have been demonstrated in InSb, and it is likely that similar devices will be realized in InSb related alloys and HgCdTe in the near future. Demonstration of a non-MIS charge transfer design would open up the monolithic approach to the IV-VI alloys. Hybrid focal planes incorporating ≳ 1000 element photodiode arrays have been realized in the III-V and the IV-VI alloys; the detector-multiplexer interface circuit will remain one of the key technical issues in the achievement of a high-performance hybrid focal plane.

Backside‐illuminated InAsSb/GaSb broadband detectors

This letter reports the achievement of a high‐performance, broad‐spectral‐band infrared detector with the InAs1−xSbx alloy system using a backside‐illuminated heterostructure approach. The basic structure of the detector is obtained with InAs1−xSbx grown by a liquid phase epitaxy technique on a GaSb substrate under lattice‐matched or nearly lattice‐matched conditions. The measured photoresponse covers the spectral range 1.7–4.2 μm with an external quantum efficiency of 65% without antireflective coating. The typical zero‐bias resistance area product is in excess of 109 Ω cm2. The typical leakage current desity is less than 10−9 A/cm2 for 100 mV reverse bias. All parameters were measured at 77 K.

Liquid phase epitaxial growth of InAs1-xSbx on GaSb

Reported here, for the first time, is the lattice matched growth of InAs1-xSbx on GaSb. The thermodynamic incompatibility of the system, i.e., the strong tendency for the In-As-Sb liquid to dissolve the GaSb substrate, was solved via a novel liquid phase epitaxial growth technique. Liquid compositions for lattice matching conditions have been determined in the 400-600°C range. Epitaxial growth has been examined for (100), (111)B and (111)A orientations. Dislocation etch pit densities for lattice matched, and near lattice matched conditions are shown to be less than 104-cm−2 and 105-cm−4, respectively. The composition of the epitaxial layers are determined by the Gandolfi X-ray diffraction technique and compositional homogeneity has been confirmed by SEM X-ray analysis. Some material related device properties which demonstrate the reproducibility of the growth technique are presented.

Liquid phase epitaxial growth of InAsxSbyPl-x-y layers on InAs

High quality InAsxSbyPl-x-y quaternary layers, which are lattice matched to InAs, have been grown successfully on InAs substrates by liquid phase epitaxy. Both Graded and constant composition InAsxSbyPl-x-y layers have been grown. In addition, the graded InAsxSbyPl-x-y layer has been used as a buffer layer for the growth of InAsl-xSbx on an InAs substrate.

1.22‐μm HgCdTe/CdTe avalanche photodiodes

A planar HgCdTe/CdTe avalanche photodiode with peak responsivity at 1.22 μm and cutoff at 1.25 μm has been fabricated successfully by liquid phase epitaxy (LPE). Avalanche gains of higher than 15 have been obtained with 1.06‐μm Nd:yttrium aluminum garnet (YAG) laser illumination. A reverse breakdown voltage of 80 V and a leakage current density of 1×10−4 A/cm2 at 40 V were measured. The peak quantum efficiency at 1.22 μm is 72% without any antireflection coating.

Charge‐coupled devices in epitaxial HgCdTe/CdTe heterostructure

An n‐channel metal‐insulator‐semiconductor charge‐coupled device has been successfully demonstrated in p‐type epitaxial Hg0.7Cd0.3Te (λco≃5.0 μm, 77 K) grown by liquid‐phase epitaxy on CdTe substrate. A three‐bit, three‐phase device was operated at 77 K, yielding a charge transfer efficiency greater than 0.995 between 5 and 50 kHz clock frequencies. Ion‐implanted n+/p diodes facilitated signal input and direct output signal detection.

Liquid phase epitaxial growth of Gal-xInxSb on GaSb by stepwise grading

The Gal-xInxSb alloy system is a potentially important material for the fabrication of middle wavelength infrared detectors and emitters. In order to develop the use of this material we have investigated the liquid phase epitaxial growth of Ga1−xInxSb on GaSb via stepwise grading in the range of 400–600°C using a horizontal slider boat in a transparent furnace. Single crystal layers of Ga1−xInxSb have been obtained for the composition range 0<x<.30. As-grown undoped layers are p-type and have been characterized by lattice constant, surface morphology, bandgap, carrier concentration and carrier lifetime.

Epitaxial HgCdTe/CdTe Photodiodes For The 1 -3 μm Spectral Region

Hgi-xCdxTe epitaxial layers have been successfully grown in various compositions, for 1-3 μm applications. n+/p junctions are formed either by a standard B-implantation into as-grown p-type layers or by doubly grown p- and n-layers. The SWIR HgCdTe photodiodes exhibit quantum efficiencies of 55-65% without AR coating. For the diodes with 1.39 μm cut-off at room temperature, the zero bias detector resistance-area (RoA) product is 4 x 10 4 Ω-cm2, and the dark current density is ~ 1 x 10 -4 A/cm2 at half-breakdown voltage. The same values of ~ 104 Ω-cm2 RoA products have also been measured for 2.4 μm cut-off photodiodes at 195K. The energy gap and temperature dependence of RoA product is in excellent agreement with the bulk limited generation-recombination model. The breakdown voltages of SWIR diodes vary from 12 volts to greater than 130 volts, depending on the Cd composition (x) and base carrier concentrations.

Millimeter‐wave generation at 110 GHz by laser modulation of a HgCdTe photodiode

Millimeter‐wave power is generated from an n+/p Hg0.74Cd0.26Te photovoltaic diode illuminated by two CO lasers of 5.467‐ and 5.478‐μm wavelengths, respectively. The output frequency is determined by the laser line separation to be 110 GHz. A maximum power of 0.75 μW is observed when the diode is dc biased at 0.5 V in the reverse direction.