The need for high-performance, low-cost IR focal plane arrays is a constant driver for materials technology improvement. Due to its high quantum efficiency and variable bandgap capability, HgCdTe is the preferred materials systems for a wide range of applications. HgCdTe crystal growth has evolved over the past fifteen years from relatively small (< 10 mm diameter) bulk multigrained ingots to large (approximately 75 mm diameter) epitaxial layers on composite substrates, but issues regarding material quality and producibility remain. Epitaxial techniques are now firmly established as the superior approaches for the growth of large-area, compositionally uniform material. Enabling this trend is the extensive progress in the size and crystalline quality of bulk lattice-matched CdZnTe substrates and the emergence of large-area heteroepitaxial substrates with CdTe and CdZnTe buffer layers on GaAs and Si. Because of the multiple interfaces, defect levels in the latter tend to be about 100 X larger than in bulk substrates; reducing these levels will be a challenge for the near future. In the meantime, bulk substrates will remain in demand for their lower dislocation densities.

The first United States Microgravity Laboratory Mission (USML-1) flew in June 1992 on the Space Shuttle Columbia. An important part of this SpaceLab mission was the debut of the Crystal Growth Furnace. Of the seven samples growth in the furnace, three were bulk grown II-VI compounds, two of a cadmium zinc telluride alloy, and one of a mercury zinc telluride alloy. Ground based results are presented, together with the results of computer simulated growths of these experimental conditions. Preliminary characterization results for the three USML-1 growth runs are also presented and the flight sample characteristics are compared to the equivalent ground truth samples. Of particular interest are the effect of the containment vessel on surface features, and especially on the nucleation, and the effect of the gravity vector on radial and axial compositional variations and stress and defect levels.

This review is oriented toward practical technological aspects of growth and applications of narrow bandgap semimagnetic semiconducting HgMnTe alloys. It summarizes recent achievements in crystal growth, device fabrication, and device characterization. Current work is focused on analyses of the growth process, approaches for the achievement of improved composition uniformity, the relationship between material properties and device performance, a comparison of performance of HgMnTe and HgCdTe devices, and new magnetic exchanged- based IR devices.

Spin coating is a simple method to produce thin copolymer films. By melting and slowly cooling a high rate of (beta) form polar crystallites can be obtained in the films, which was confirmed by X-ray diffraction patterns. By poling at bias fields above 100 V/micrometers , a high spontaneous polarization, and a high pyroelectric coefficient, low dielectric constants and dielectric losses can be achieved. The spontaneous polarization and the Curie point increase with rising context of VDF, while pyroelectric coefficient and dielectric constant decreases. Compositions with a VDF molar content of 70% to 80% are best suited for applying to pyroelectric sensors. the chosen P(VDF/TrFE) shows a spontaneous polarization of 8 (mu) Ccm^-2 and a pyroelectric coefficient of 3.5 nCcm^-2K^-1, a dielectric constant of 8 and a dielectric loss of about 0.018 at 25 degree(s)C. With the help of a computer simulation, the optimum sensor design was achieved in the case of single-element sensors and linear arrays. The care is a self-supporting carrier membrane of about 500 nm Si₃N₄ and 150 mm SiO₂, made by backside etching of silicone with a spin coated (1 - 2) micrometers thick P(VDF/TrFE) film. Built up single-element sensors and linear arrays distinguish themselves by a high voltage responsivity and a high signal-to-noise ratio. They are quite comparable to common sensors of lithium tantalate.

Results are presented on uniform deposition of CdTe, HgTe, and HgCdTe thin films by atomic layer epitaxy (ALE) using Hg-, Cd-, and Te-alkyl chemistry at deposition rates of a few monolayers/min. In contrast, we also discuss the deposition of uniform CdTe(Zn) films on large-area alternative substrates by conventional metalorganic chemical vapor deposition (MOCVD) at growth rates of a few monolayers/sec. Excellent thickness and compositional uniformity (1% standard deviation) have been achieved for MOCVD CdTe(Zn) films on 75 mm GaAs and Si substrates. ALE growth of CdTe was carried out over a wide range of temperatures (250 to 320 degree(s)C) and reactant partial pressures. ALE of HgTe with excellent uniformity and surface morphology has been achieved over the temperature range of 120 to 160 degree(s)C. HgCdTe layers were also grown by alternately depositing HgTe and CdTe on CdTe substrates and then interdiffusing them at higher temperatures. FTIR measurements of a 0.43 micron thick HgCdTe film deposited by this technique showed excellent characteristics.

A brief review is given of recent results to assess the capability of metalorganic molecular beam epitaxy for the low-temperature growth of high-quality low-carrier-concentration CdTe and HgCdTe alloys. In particular, studies of this technique to produce highly uniform HgCdTe material and the extension of the gas source doping of CdTe and HgCdTe with ethyliodide so as to obtain back-doped electron concentrations from 10¹⁵ to 10¹⁸ cm^-3 are reported. Some preliminary results on the growth of ternary CdTe/HgCdTe superlattices and the p-type doping of CdTe with As will also be presented. The electrical and optical properties of these materials were determined by resistivity and Hall effect, photoluminescence, and IR transmission measurements between 300 and 10 K.

We used molecular beam epitaxy to codeposit IrSi₃ films on p-type Si(111) and Si(100) substrates at elevated temperatures. Seemann-Bohlin x-ray diffraction reveals the formation of IrSi₃ at temperatures as low as 450 degree(s)C. We find that the growth of 100 angstroms IrSi₃ films on Si(111) and Si(100) substrates is similar to that of 450 angstroms IrSi₃ samples. Using low-energy electron diffraction, Bragg-Brentano x-ray, and transmission electron microscope (TEM) diffraction we identify a previously unreported c-axis oriented growth mode for IrSi₃ films deposited around 700 degree(s)C on Si(111) substrates. Indexing of TEM diffraction patterns suggests that the lattice constants for IrSi₃ in these thin films are the same as values derived for bulk IrSi₃ by other researchers. Atomic force microscopy and TEM images show the formation of continuous 100 angstroms IrSi₃ films at temperatures as high as 630 degree(s)C on Si(100) substrates and the formation of epitaxial IrSi₃ islands for temperatures above 670 degree(s)C on Si(111).

HgCdTe MBE technology is becoming a mature growth technology for focal plane array applications. Device quality materials have been growth with alloy compositions required for SWIR to VLWIR applications. X-ray characterization results indicate that the epilayers exhibit FWHM of about 25 arc-sec, which is indicative of high quality materials. In addition to x-ray data, the observation of low defect density (EPD < 2 X 10⁵/cm²), long minority carrier lifetime (t equals 1 micro-second for x equals 0.23, n equals 2 X 10¹⁵/cm³), and efficient IR photoluminescence, all attest to the device quality of HgCdTe epilayers grown by MBE. The breakthroughs to achieve In(n-type) and As(p-type) doping in-situ provide greater flexibility for fabricating advanced heterojunction devices. High-performance IR devices that use HgCdTe MBE materials are demonstrated. The additional development of drying etching and passivation in an ultrahigh vacuum environment coupled with an MBE growth system should lead to cost-effective and flexible manufacturing of devices for military and commercial applications.

This paper describes a unique and high-performance 1024-element linear In_xGa_1-xAs/InAs_yP_1-y detector array for environmental sensing applications in the 1 micrometers to 2.6 micrometers spectral range. The detector array was fabricated using hydride vapor phase epitaxy grown material. The size of each pixel of the detector array is 13 X 500 micrometers ² with 25 micrometers pitch. Improvements in dark current and quantum efficiency were realized by optimization of crystal growth, thermal annealing, and diffusion techniques. Transmission electron microscopy analysis of the fabricated structure was used to find the effect of thermal annealing on the dislocation density and the leakage current. The measured results of the 1024-element detector array sliver is presented.

The photosensitivity of lead chalcogenides in the IR region has been known for a long time. These detectors exhibit wide range of electrical characteristics. A cheap and easy chemical bath deposition process has been utilized to deposit PbS onto glass substrates. Well adherent nonporous `p' type PbS films of thickness 1 - 1.5 microns were obtained. These films, after heat treatment, showed a dark resistance of 0.5 - 1 M(Omega) with a high signal-to-noise ratio of 1000 with a D^* (800 degree(s)C, 500 Hz, 2 Hz) of 2.6 X 10¹⁰ cm Hz^1/2 W^-1.

We report for the first time the growth of high quality Zn Te epilayers on silicon substrates by Metal Organic Vapor Phase Epitaxy (MOVPE). ZnTe layers up to 7μm thick were grown on (001) silicon substrates at 420°C-450°C substrate temperatures. The layers were mirror shiny and smooth, devoid of growth features like layered or stepped structures. The x-ray double crystal diffraction showed that best ZnTe layers exhibited Full Width at Half Maximum (FWHM) of 110 arc seconds. Further optimization of the growth procedure will make this material very useful for the potential development of iow cost infrared focal plane arrays and other optoelectronic devices which use direct wide band gap ZnTe.

Molecular-beam epitaxy (MBE) has been utilized to deposit single crystal films of ZnTe and CdZnTe/ZnTe onto Si(100) and Si(112) substrates. Parallel epitaxy of ZnTe(100) and CdZnTe(100)/ZnTe(100) has been observed for growth on Si(100) substrates misoriented from 0-8 degrees towards the [011] direction. With ZnTe initiation layers, high quality CdZnTe(100) films have been demonstrated on both 4° and 8° misoriented Si(100) with x-ray rocking curve FWHM as narrow as 158 arc-seconds, which is comparable to that obtained with GaAs/Si composite substrates. The observed surface morphologies are superior to those obtained on GaAs/Si composite substrates. HgCdTe(100) films with x-ray FWHM as low as 55 arcseconds and average etch pit densities of 5 x 106 cm2 have been deposited by liquid phase epitaxy on these MBE CdZnTe/ZnTe/Si(100) substrates. On vicinal Si(1 12) substrates, ZnTe films are observed to nucleate in either the (1 12) or its twin (552) orientation depending on the misorientation of the Si substrate away from (1 12). For Si(1 12) misorientations of 5° or 10° towards from the [1 1-1] direction, ZnTe nucleates in a parallel (1 12) orientation, while for misorientations of 0° or 5° away from the [1 1-1] direction, ZnTe is observed to nucleate in a (552) orientation. CdTe deposited on ZnTe/Si(112) is observed to nucleate in the same orientation as the ZnTe. CdTe(552) epilayers are of substantially higher quality than (1 12)oriented films. X-ray rocking curves as narrow as 1 10 arc-seconds have been observed for the CdTe(331) reflection in the case of (552)-oriented epitaxy.

MBE growth and IR device fabrication with epitaxial IV-VI layers on Si-substrates is reviewed and some new results are included. Epitaxy is achieved using a stacked BaF₂/CaF₂ or CaF₂ buffer layer. While photolithographic delineation techniques are somewhat difficult with BaF₂ (which is soluble in water), reliable wet-etching techniques are easy with the CaF₂ buffer. Photovoltaic IV-VI sensors on Si(111) substrates are fabricated with cut-off wavelengths covering the whole atmospheric 3 - 5 and 8 - 14 micrometers window. They offer the possibility for low cost IR focal plane arrays with sensitivities similar to MCT, but with much less demanding material processing steps.

The molecular beam epitaxially growth of (001) Hg_1-xCd_xTe-HgTe superlattices has been systematically investigated. The well width as well as the period were determined directly by X-ray diffraction. This was accomplished for the well width by exploiting the high reflectivity from HgTe and the low reflectivity from CdTe for the (002) Bragg reflection. Knowing the well and barrier thicknesses we have been able to set an upper limit on the average composition of the barriers, x_b, by annealing the superlattice and then measuring the composition of the resulting alloy. x_b was shown to decrease exponentially with decreasing barrier width. x_b is appreciably smaller in narrow barriers due to the increased significance of interdiffusion in the Hg_1-xCd_xTe/HgTe interface in narrow barriers. The IR photoluminescence was investigated at temperatures from 4.2 to 300 K. Pronounced photoluminescence was observed for all superlattices in this temperature range.

We report on the observation of normal incidence IR photoconductive detector response in ellipsoidal valley n-type GaSb-AlSb multi-quantum well samples, grown on (001) GaAs substrates by molecular beam epitaxy. Photoconductors were fabricated and IR detector response was measured using Fourier transform IR spectroscopy. Detector response was observed in the long wavelength IR band at (lambda) equals 8.5 micrometers for an operating temperature of T equals 77 K, and agrees well with absorption data. We also show preliminary results on a method for extending the intersubband transition energies to longer wavelength.

Large-area GaAs/AlGaAs quantum-well IR detector arrays need highly uniform layer thicknesses to meet response wavelength uniformity requirements. We have measured the variation in absorption wavelength with layer thickness in a miniband transport (MBT) IR detector consisting of multiple periods of doped quantum wells with superlattice barriers. The absorption wavelength and quantum well width were determined in samples taken from the radius of a detector wafer. A model was developed to fit the wavelength versus well width data from the grown wafer. For small changes in well width the wavelength varies linearly with well width. The MBT IR detector structure grown for this experiment had a slope of 0.11 micrometers /angstroms, corresponding to a thickness deviation of 0.6% for a wavelength deviation of 0.05 micrometers . The model can be used to design other MBT IR detectors with slightly higher thickness tolerances. A uniformity test structure was developed for tracking layer thickness and composition variations over epitaxial wafers. Examples of typical molecular beam epitaxy (MBE) uniformities from a single- and a multiwafer MBE are presented.

We present experimental results of investigation MQW IR detectors by photocurrent spectroscopy under different electric field condition. It is found that photocurrent exhibits different line shapes, maximum location and values at various values and sign of bias. These results and cause of existence photocurrent at zero bias are discussed.

Three-dimensional quantum wells are composed of a small cube of the wideband-gap semiconductor and the narrowband-gap semiconductor, piled alternatively in space, the small cube of the wideband-gap semiconductor is all the same to that of the narrowband-gap semiconductor, effective mass schrodinger's equation is found in periodic boundary conditions, electronic state in 3D quantum wells is described.

Detection and identification of impurities and defects in semiconductor materials has long been a topic of technological importance. Of particular interest is the activation energy of the impurity/defect states. For narrow-gap materials magneto-optics is a technique of choice, since resonant transitions from impurity-to-band or band-to-impurity states allow for the precise determination of just these states. Two magneto-optical techniques, resonant magneto-optical and resonant impact ionization spectroscopy, have been successfully used to investigate intrinsic magnetoabsorption and shallow and deep impurity and defect levels in bulk InSb and in bulk and liquid-phase-epitaxy HgCdTe. In this paper, these magneto-optical techniques will be reviewed, concentrating on their versatility and sensitivity for the detection and identification of weak absorption process such as those expected when impurity and defect levels are involved. A discussion of the mechanisms and results for a variety of magneto- optical phenomena from both InSb and HgCdTe will be given and discussed.

This paper reports the change in the bulk transport properties of p-type MCT samples induced after a rapid thermal annealing (RTA) process. This change is produced homogeneously within the crystal without interchange of mercury with the surrounding atmosphere. The carrier concentration varies toward an equilibrium value that depends only on the annealing temperature. For the material and temperatures investigated (250 to 450 degree(s)C) the equilibrium carrier concentration depends exponentially on the inverse of the temperature, its value ranges between 7.8 X 10¹⁶ and 4.5 X 10¹⁷ cm^-3. The time needed to reach the equilibrium is a function of the temperature, varying from 10 seconds to 420 degree(s)C to 200 seconds at 250 degree(s)C. Hole mobility is also affected by the RTA process, being its variation also a function of the process temperature and time, but with different values of the evolution parameters. A saturated temperature independent positron lifetime of 310 ps has been measured in all the samples. We attribute this value to presence of a high concentration of mercury vacancy defects, where positrons are annihilated.

Transient thermal expansion, heat generation and conduction, nonlinear laser heating, and subsequent melting behaviors of polysilicon/oxide/silicon wafer `sandwich' structures have been investigated via a laser pump-probe technique. Laser processing, damage, and characterization of bulk semiconductor materials has been extensively investigated. However, less is known about the mechanism of laser-induced damage for multilayer structures such as CCD imaging arrays. In order to develop damage resistant sensors and better isolation for sensors used in laser environments, it is necessary to understand the processes contributing to the laser hardness and damage of these sensors. We designed experiments to measure the transient thermomechanical and laser-damage characteristics of multilayer systems that resemble CCD devices. The final objective was to gain some insight into the dominant mechanisms responsible for laser-induced degradation in CCD imaging arrays and devices of similar structures. Positive identification of a precursor event signaling the onset of catastrophic damage and identification of the weakest link elements on the sensor array will be essential for making design or processing modifications to improve hardness. It is our goal in this paper to contribute to the above objectives by describing investigations of laser-induced damage to silicon-based multilayer structures.

The thermoelectric properties of n-type Hg_0.79Cd_0.21Te (MCT) and of MCT layers with n-p-n structure were investigated in transverse magnetic fields (B (perpendicular) $DELT; 0 <EQ B <EQ 12 kG) using the lateral gradient method at temperatures between 15 K and 300 K. The experimental results were analyzed regarding the contributions of electrons and holes to the magneto-thermoelectric effect and the scattering mechanisms involved. The analysis is based on a nonparabolic conduction band and Landau quantization together with expressions for the band gap, the intrinsic carrier density, and the magnetoresistance. The magneto-thermoelectric effect was found to be a useful nondestructive tool for determining the doping and composition of the constituent layers of MCT n-p-n structures.