The experimental optical absorption coefficient of HgTe/Hg_0.32Cd_0.68Te superlattices with a wide range of well and barrier widths have been compared with theoretical calculations. There is good agreement with experiment if the Cd concentration profile across the as-grown interfaces is assumed to have the shape given by an error function together with an additional Cd concentration of 3% in the quantum wells. The latter concentration was experimentally confirmed. If diffusion is responsible for this concentration profile then a dependence on depth should be present, however, none was observed. Therefore the Cd concentration profile across the interfaces of an as-grown HgTe/Hg_0.32Cd_0.68Te superlattice does not result from interdiffusion of the interfaces during growth. In other words, growth mechanisms do not involve interdiffusion of the interfaces.

High quality 2 inch Hg_1-xCd_xTe/Sapphire structures are grown by an isothermal vapor phase epitaxy process starting from MOCVD CdTe/Sapphire hybrid substrates. HgTe growth and CdTe/HgTe solid state interdiffusion processes produce the transformation of the starting CdTe layer into a compositionally controlled Hg_1-xCd_xTe film on the inert base sapphire substrate grown. By using experimental growth conditions involving HgTe/CdTe interdiffusion rates higher than HgTe growth rates, in depth compositionally uniform Hg_1-xCd_xTe films can be obtained in a really simple one-step process. A 2-zone open tube vertical reactor improved for 2 inch wafers has been used for the present process, making it very attractive for manufacturing purposes. Morphological, optical, electrical, and structural characteristics of the iso-VPE mercury cadmium telluride on sapphire structures are reported witnessing their technological power as infrared materials.

Molecular-beam epitaxy (MBE) has been utilized to deposit single crystal epitaxial films of CdTe(112)B and HgCdTe(112)B directly onto Si(112) substrates without the use of GaAs interfacial layers. The films have been characterized with x-ray diffraction and wet chemical defect etching, and IR detectors have been fabricated and tested. CdTe(112)B films are twin- free and have x-ray rocking curves as narrow as 72 arc-seconds and near-surface etch pit density (EPD) of 2 X 10⁶ cm^-2 for 8 micrometers -thick films. HgCdTe(112)B films deposited on Si substrates have x-ray rocking curve FWHM as low as 92 arc-seconds and EPD of 8 - 30 X 10⁶ cm^-2. HgCdTe/Si infrared detectors have been fabricated with R₀A equals 4.3 X 10³ (Omega) -cm² (f/2 FOV) and 7.8 micrometers cutoff wavelength at 78 K to demonstrate the capability of MBE for growth of large-area HgCdTe arrays on Si.

IV-VI materials (PbTe, PbSe, Pb_1-xSn_xSe) are grown by molecular beam epitaxy onto Si(111) and Si(100) substrates. Device quality layers are obtained on Si(111), if a very thin CaF₂, or a stacked CaF₂/BaF₂ buffer layer is employed. For these layers, thermal mismatch strain relaxation occurs by glide along the main {100} glide planes inclined by 54 degrees with respect to the surface. Cumulative plastic deformation on temperature cycling up to 500% was observed even at cryogenic temperatures, while the structural quality of the layers was only slightly adversely affected by such extreme plastic deformations. Interaction probabilities between moving dislocations were estimated to be below 10^-5. Epitaxial growth of IV-VI materials directly on Si (without buffer layer) is possible, too. However, the structural quality is inferior. On Si(111), PbSe with either (100), (111) or mixed (111) and (100) orientation, depending on growth temperature, is obtained. Single oriented (100)PbSe layers result on Si(100). Strain relaxation occurs via the same mechanisms as for layers grown with buffer layers: On Si(111), strain relaxes by slip, while on Si(100), both relaxation by plastic deformation as well as by cracking is observed. The latter occurs for layers thicker than about 0.5 micrometers only.

This paper describes the growth and properties of micro-machined semiconductor microbolometers. These thermally isolated structures are employed in uncooled infrared detectors developed at the Defence Science and Technology Organisation (DSTO). Recent research is focused towards developing high performance bolometers from the amorphous and more recently the microcrystalline phases of the SiGe:H material system. Particular attention is given to materials and material growth techniques that maximize the responsivity and minimize the electronic excess noise. The basic design, materials science, and performance of these bolometers for detecting infrared radiation are described in this paper.

We present a review of the recent progress in the doping of HgCdTe grown by molecular beam epitaxy. A detailed analysis of the unintentional/intrinsic, n-type, and p-type doping is presented. Our results show that CdZnTe substrates should be carefully screened to reduce the out-diffusion of impurities from the substrate. N-type HgCdTe layers exhibit excellent Hall characteristics down to indium levels of 2 X 10¹⁵ cm^-3. Electron mobilities in the range of (2 - 3) X 10⁵ cm²/vs at 23 K were obtained. Measured lifetime data fits very well with the intrinsic band-to-band recombination. However, below 2 X 10¹⁵ cm^-3 doping levels, minority carrier lifetime is limited by Schockley-Reed recombination. We have implemented planar doping with arsenic as p-type dopant during MBE growth. Our results clearly indicate that arsenic incorporates as an acceptor dopant during the growth of MBE HgCdTe.

We have studied InAs/GaSb superlattices (SLs) grown with either InSb-like or GaAs-like interfaces (IFs) on top of a GaSb buffer layer on (100) GaAs substrates. The InAs layer thickness was varied from 4 to 22 monolayers (ML) while the GaSb layer thickness was kept fixed at 10 ML. Two-dimensional high-resolution x-ray diffraction space maps using symmetric and asymmetric reflections, allowed us to determine independently the lattice constants parallel and perpendicular to the growth direction. The GaSb buffer layer was found to be fully relaxed whereas the SLs with InSb-like IFs were found to be coherently strained to the lattice parameter of the buffer layer for InAs layer thicknesses exceeding 6 ML. For SLs with GaAs-like IFs a comparison of measured with simulated x-ray reflection profiles enabled us to deduce the strain distribution within the SL stack, which showed increasing strain relaxation with increasing distance from the buffer layer. The dependence of the effective band gap on the SL design assessed by photoluminescence and photocurrent spectroscopy, is compared with theoretical calculations.

The concept of integrated technique of thermally activated spectroscopy (TAS) of localized states (LS) in forbidden gap of semiconductors and insulators (intrinsic and impurity centers of trapping, recombination, luminescence) taking into account the interactions of the charge delocalization and transport processes in heterostructures is developed. In the widely used advanced TAS techniques (deep level transient spectroscopy -- DLTS, fractional thermally stimulated depolarization -- FTSD) the interaction of thermogeneration and trapping with transport and spatial redistribution of charge carriers (i.e., the relationship of transitions on to energetic and spatial coordinates) are considered as negligible, that results in incorrect applications of these techniques for such interesting objects as amorphous and disordered materials, thin films, and heterostructures. As shown by numerical simulations and experiments, the charge TAS realizes the high threshold sensitivity, high stability to anomalous effects of spatial charge redistribution, and may be used on all stages of relaxation process with arbitrary kinetic parameters.

We have developed a nondestructive evaluation method for HgCdTe. We focused on laser beam induced current (LBIC) which features a high specific resolution and nondestructive evaluation. The LBIC technique shows the electrically active regions in HgCdTe wafer as an image. We have considered the measurement temperature versus the LBIC signal. The LBIC technique at room temperature (300 K) can be used to evaluate non-uniformities in carrier concentrations in HgCdTe more sensitively. Using etch pit studies and secondary ion mass spectroscopy (SIMS), we have identified that non-uniformities of carrier concentration in the HgCdTe wafer arise from metal impurities around dislocation clusters. This nondestructive technique is useful for screening HgCdTe wafers before fabricating devices.

A nondestructive characterization technique to determine free carrier concentration and mobility that is applicable to most n-type semiconductors, including infrared detector materials such as InSb and HgCdTe, is presented. The technique utilizes absorption and Faraday rotation in regions of the spectrum where these phenomena are due mostly to the free carriers themselves. Carrier concentration is directly proportional to the free carrier component of the rotation signal. Free carrier mobility is proportional to a simple ratio of the free carrier rotation to the free carrier absorption. Good agreement with Hall mobility data was obtained using a simpler version of this technique at room temperature. The proportionality constant is actually a complex quantum mechanical quantity that is temperature- and material-dependent. In this study, absorption data was obtained in the temperature range 77 K to 300 K in HgCdTe, n-type InSb, GaAs, and Si. Rotation data was measured at 300 K and calculated for lower temperatures using known values of electron effective mass and refractive index to determine this constant and make it available for practical mobility determinations at various infrared detector operating temperatures.

We review recent progress in the development of quantum confined structures based on the InAs-GaSb-AlSb family of semiconductors. The results of transport and quantum transport experiments are summarized to illuminate band structure features and carrier scattering mechanisms that are key to device applications. The unique band structure engineering possibilities enabled by the presence of L-valleys in the conduction band are explored, as well as, the general progress in band structure calculations and modeling of complex multi-layers. A primary emphasis is the flexibility of the InAs-GaSb-AlSb material system as the basis for a wide variety of E-O modulators, frequency doublers, infrared diode lasers, and other devices.

An etch process was developed to determine the dislocation density on <111>B - Hg_1-xCd_xTe-epilayers grown by liquid phase epitaxy from a tellurium-rich solution. A correlation between the etch pit density and the Cd_1-yZn_yTe-substrate material properties is found. Additionally the yield of photovoltaic diode performance strongly depends on the value of these measured dislocation densities. This method acts as a pass/fail evaluation for the epilayers used in our infrared device fabrication.

A wavelength tunable far-infrared (FIR) detector based on the interfacial workfunction (IWF) between a heavily doped absorber/emitter layer and a lightly doped (or intrinsic) layer (same material) forming a homojunction is presented. The concept somewhat similar to the classic photoelectric effect was successfully demonstrated using commercial p-i-n structures. The forward biased Si, Ge, and InGaAs samples were operated at cryogenic temperatures. Threshold wavelengths ((lambda) _t) from around 40 - 220 micrometers for Si and up to 240 micrometers for Ge were experimentally obtained. A model was developed to analyze the photoresponse and the dark current leading to detector figures of merit. The effect of the space charge region on the barrier height and the barrier position is investigated for a thick sample similar to the p-i-n structures.

A 128 multiplied by 128 GaAs/GaAlAs quantum well infrared (QWIP) sensing array with a 2- D grating and indium bumps has been fabricated. The array has been characterized prior to flip chip bonding, both electrically and optically. The obtained responsivity and dark current of selected pixels in the array indicate high material uniformity. Design and processing issues are discussed.

Recently, significant advances have been made in both the application and production of the narrow gap, antimonide compound semiconductors. Growth of InSb and GaSb at 3 and even 4 inch diameters has been achieved with good homogeneity and acceptable defect density. Advances are being made to achieve a wafer surface finish suitable for direct epitaxy. New binary applications for large-area focalplane detector arrays, high resistivity substrates and thermophotovoltaics, and for the ternary (Ga,In)Sb are discussed.

A CoSi₂/strained-Si_1-xGe_x-Schottky barrier detector is proposed for detection of infrared radiation in the 3 - 5 micrometers window. It could be a substitute for PtSi/Si-Schottky barrier detectors, which have already been integrated with readout electronics, but which imply the disadvantage of having the metal Pt in the line as a possible source of contamination. A silicidation study on strained Si_1-xGe_x-layers with sacrificial Si-layers on top has been carried out to realize CoSi₂/strained-Si_1-xGe_x-interfaces, which will form the heart of the detector. The possibilities to integrate this detector with readout electronics are critically reviewed. First CoSi₂/Si_1-xGe_x-detectors have been processed which yield barrier heights as low as 229 meV.

A simple method for controlling the thickness of PtSi for infrared detectors is presented. Thicknesses of PtSi in the range of 2 - 5 nm can be controlled via the reaction kinetics of the silicidation. Compared to conventional furnace anneal, the thickness and homogeneity of the resulting PtSi-layers are independent of the deposited Pt-thickness. Superior uniformity, lower continuous film thicknesses of the PtSi-layers, and smoother PtSi/Si-interfaces than possible by conventional furnace anneal are achieved by applying this technique.

Ellipsometry is a powerful technique for the determination of complex refractive indices ^n equals n plus ik of thin absorbing films deposited on a substrate. If the films are deposited onto an opaque substrate, the calculation methods are well-known. However, sometimes it is advantageous for some other reason to deposit the films onto a transparent substrate. In this case the light reflected from the back surface of the substrate must also be taken into account. If the thickness of the substrate is much larger than the coherence length of the light, there is no correlation between the phases of the light beams reflected from the boundaries of the thin film and the beam reflected from the back surface of the substrate. Therefore, it is not possible to calculate the absolute phase of the total reflectance of the system, i.e. the film plus substrate. However, for the determination of the ellipsometric coefficients the relative phase must be known. In this publication a method of calculating the ellipsometric coefficients of such a system is presented. Instead of calculating the absolute phase, this method is based on the calculation of reflected intensities for arbitrary angles of polarization taking into account the relative phase shift at each boundary. Comparisons between measurements of ellipsometric coefficients of well-known materials and the calculations based on this method show excellent agreement.

Theoretical analysis of the relation between amplitude of photothermal signals in nonuniform samples and modulating frequency used photothermal deflection spectroscopy (PDS) shows: compared with the curve of logarithmic amplitude of PDS signals of uniform substrate materials, the curve inclination of logarithmic amplitude via frequency omega increases when absorptive index of p-layer is smaller than that of n-layer in nonuniform Gap:N, otherwise, it decreases. By comparing this result with experimental results, we can obtain concentration distribution of nitrogen in p-layer and n-layer of Gap:N. Meanwhile, absorption spectra under different modulating frequencies at room temperature have been measured, and the possibility of measurement of optical and thermal characteristics at different depth of nonuniform samples under various modulating frequencies is indicated. In a word, this paper suggests a method to measure internal characteristics of nonuniform materials without damage, which has been verified in experiment.

Although there are several materials which have properties that make them attractive as IR window materials for electro-optical systems operating in the 8 - 12 micrometer range, no single material possesses the superior mechanical, optical, and thermal properties required for current supersonic window applications. Hence, composite structures have been examined for use in airborne window systems to maximize erosion resistance, provide high optical quality and maintain thermal stability. This paper reports the identification of a suitably robust bonding glass possessing the needed thermal, mechanical and optical properties for use in a ZnSe/glass/diamond composite structure. Recent results of our property characterization studies on candidate glasses are reported.

Birefringence and x-ray diffraction experiments have been carried out on Kevlar 49^R fibers under tensile stress to monitor structure changes under the stress field. The origin of the observed birefringence is discussed in some detail. Results from theoretical calculations using semi-empirical molecular orbital techniques are presented and contrasted to the experimental observations. The calculations involved the estimation of chain polarizability and were performed under simulated stress conditions using the AM1 Hamiltonian in MOPAC. Polarizability is then used to calculate the birefringence as a function of tensile stress, by using existing internal field theory. This theoretical approach is applied to predict the optical properties of highly oriented extended-chain polyethylene, as well as those for poly(p' phenylene therephtalamide); the latter being the base polymer in Kevlar fibers. Results reveal reasonable birefringence predictions when compared to available experimental results in the literature. Also, it is found that the contribution from orienting crystallites under the stress field, to the measured birefringence in Kevlar fibers, is only a small fraction of the total. However, the calculations predict a significant contribution from deformation (extension) at the molecular level.

Spiropyran doped poly(vinylcarbazole) films have been used to record reversible holograms. The real-time diffraction profile was studied for different exposure energies, film thickness and dye concentration. The photoinduced reversible color change between thermally stable and metastable states of spiropyran molecules can modulate the absorption and the refractive index of the spiropyran doped polymer film. Erasable holograms can be recorded in either stable or metastable states of the spiropyran doped PVCz films of 10 and 50 micrometers prepared by gravity settling method. The grating constant achieved was delta equals 0.58 micrometer using 350 nm UV line of a Krypton-ion laser. It has been found that write, read, and erase (WRE) cycles can be performed repeatedly. High efficiency erasable holographic recording at 350 nm has been performed in spiropyran doped PVCz films and a diffraction efficiency greater than 10% has been achieved.

Azo-dye doped polymer (ADP) systems have been the focus of many research groups for realizing various holographic applications for the past twenty years due to their remarkable optical properties such as grainless media, real-time capabilities, dynamic polarization holographic recording, etc. In this paper, we are reporting the photorefractivity of azo-dye doped Poly(methyl methacrylate) (PMMA) films. Under actinic lighting (lambda equals 488 nm), real-time dynamic phase holograms resulting from a local change in refractive index, with reasonable high diffraction efficiency, have been recorded and a maximum of 10% has been achieved. The diffraction efficiency obtained is higher than the similar earlier reported systems. The real-time kinetics of photoreversibility (bleaching and evolution) of azo dyes in PMMA matrices has also been studied. Some interesting applications in optical processing have been realized, exploiting the special properties of ADP systems such as complete auto- reversibility, high rise and erase times, absence of memory effect, and uniform write/read/erase (WRE) cycles.

We present the results of a systematic photoluminescence study of ZnGa₂O₄:Mn phosphor powder. This phosphor exhibits bright green luminescence with a spectral peak at 2.46 eV and CIE chromaticity coordinates of x equals 0.073 and y equals 0.696 at room temperature. At low temperatures the luminescence consisted of three components assigned to the ⁴T_1-⁶A₁ inner transition of the 3D electrons of Mn²⁺ ions located on different sites of the host crystal. Selective excitations were used to validate the assignment of these features based on a strong-field scheme. The photoluminescence lifetime showed a single exponential decay of about 4 ms and at T equals 1.6 K an optical phonon related fine structure [E_phonon equals (8.2 plus or minus 0.2) meV] of the main photoluminescence line was observed. These results indicate that Mn-doped ZnGa₂O₄ has the potential to serve as a green phosphor for field emission display (FED) devices. The CIE coordinates of the green emission measured for this phosphor powder are also sufficient to produce a wide color gamut and a true white color when combined with other red and blue phosphors in FED display devices.

As a nondestructive, contactless characterization method time dependent charge measurements (TDCM) are used for the investigation of high resistivity CdTe doped with vanadium or titanium. TDCM is presented as a multi-purpose technique which allows for the examination of the resistivity, the thermal activation energy of the charge carriers, the photosensitivity and the surface voltage (SPV). Strong axial variations of the physical properties are observed as a consequence of the segregation of the dopants.

The coplanar electrode for lithium niobate automatic polarization controller is superior to other approaches proposed in many aspects. We have analyzed the half-wave voltages for the automatic polarization controller with regard to the design parameters of the coplanar electrode. The numerical analysis using combined FD-CM method is proposed. The optimal electrode design for approach minimum control voltages is analyzed. The numerical method can reduce calculation time compared with using FDM method only.

The possibility of use of the thermal emission of a complex semiconductor compound for determination of its forbidden band gap and, hence, the composition is examined. Measurements were carried out on p-type Hg_1-xCd_xTe films with 0.197 <EQ X <EQ 0.233 at room temperature.

Thin copperphthalocyanine layers have been deposited on quartz glass substrates and investigated by means of transmission and reflection spectroscopy. The film thickness ranged between 20 nm and the subnanometer region. The determination of the optical constants allowed the estimation of the oscillator strengths for the relevant molecular transitions. A thickness dependence of the Q-band absorption maximum position could be established for layers with a thickness below 5 nm. The contributions of several physical mechanisms to such lineshifts are discussed.

The electrical and optical properties of iodine doped n-type HgCdTe alloys and superlattices grown by metalorganic molecular beam epitaxy using ethyliodide are reviewed. The rationale for the use of iodine rather than indium as the dopant species and the incorporation kinetics of iodine at the growth surface are discussed. The electrical and optical properties of iodine- doped CdTe and HgCdTe (x equals 0.24) are presented for carrier concentrations between 10¹⁵ and 10¹⁸ cm^-3, as determined by Hall effect measurements and low- and room-temperature photoluminescence spectroscopy. These samples show strong room temperature excitonic effects due to free exciton and band to band recombination as determined by photoluminescence excitation spectroscopy. The electrical and optical properties of iodine-doped HgCdTe-CdTe superlattices also are discussed based on magnetoluminescence measurements in tilted magnetic fields of up to 7 Tesla in Voigt and Faraday geometry.