Transient lifetime measurements on p- and n-type Hg1−xCdxTe epitaxial films, grown by the MOCVD-interdiffused multilayer process (IMP) on CdTe and CdZnTe, are reported. Lifetimes have been measured on undoped n-type, vacancy and arsenic doped p-type (HgCd)Te for x-values of 0.20–0.28 over the 25K–300K temperature range. Lifetime characterization has been carried out primarily by non-contact transient millimeter wave reflectance as well as by standard photoconductive decay. It is shown that Auger limited lifetimes are achievable in undoped n-type material. N-type lifetime results are analyzed within the framework of a multilevel Shockley-Read model which provide insight into the nature and density of defect states in the material. In p-type (HgCd)Te, for the same carrier concentration, longer lifetimes are obtained by As-doping than in vacancy doped material.

The incidence of compositional and structural inhomogenieties in MSM detectors based on Hg1−xCdxTe/GaAs and Hg1−xCdxTe/GaAs/Si has been examined by nuclear microprobe. With a 2 MeV He+ beam focussed to ≤5 μm, the microprobe has demonstrated the capability for RBS channelling in the active region of a Hg1−xCdxTe device and the imaging of defects by Channelling Contrast Microscopy (CCM). A series of linear growth defects in some Hg1−xCdxTe devices were identified using CCM. The channelling RBS spectra from these regions have shown an increase in χmin compared with the surrounding high quality crystal. The occurence of these defects was associated with a degradation in the performance of affected devices in an array. RBS spectra have also revealed the presence of an anomalous CdTe layer, correlating with a significant reduction in dark current and increase in breakdown voltage of these devices. RBS channelling of individual devices has identified differences in χmin between arrays which were prepared under equivalent conditions of growth and processing.

Hg1−xCdxTe crystals with x˜0.2 were grown by the traveling heater method (THM), in either the [111]A or [111]B directions, using oriented CdTe seeds. Twins are sometimes formed during the growth of these crystals. In crystals grown in the [111]A direction the twins, of orientation [511]B, are constantly growing at the expense of the original [111]A oriented grain. Growth in the [111]B direction, on the other hand, suppresses the growth of the twin domain. Photodiodes and capacitors realized on the (111)A plane are markedly superior to those on the twin plane, [511]B. The difference is due to higher fixed charge and larger fast surface state densities in the case of the [511]B plane. These effects are explained by the lattice structures in the {111} and {511} planes and their possible influence on surface reactivity.

HgCdTe MBE technology is becoming a mature growth technology for infrared focal plane array applications. The ability to dope HgCdTe with In(n-type) and As(p-type) dopants in-situ provides greater flexibilities for fabricating heterojunction devices. In this paper, we will first discuss the current status of HgCdTe MBE growth and then focus on the key results in the control of In(n-type) doping, various approaches and breakthroughs in the growth of As(p-type) doped HgCdTe and issues related to doping such as memory effects and dopants activation. In addition, device results from double layer heterojunction structure(DLHJ) will be briefly discussed.

Both the cadmium vacancy (Vcd) and the tellurium vacancy (VTe) in CdTe are identified by means of electron paramagnetic resonance (EPR). The Vcd is a double acceptor and the EPR spectrum is observed in its single negative charge state. The symmetry is found to be trigonal, which can be explained in a model in which the hole occupies a dangling bond t2 orbital and the orbital degeneracy is removed by a static Jahn-Teller distortion. The hyperfine interaction shows that the hole is localised on one of the four Te neighbours. The EPR spectrum of VTe+ reveals cubic (unperturbed) symmetry and the hyperfine structure shows that the unpaired electron is equally spread over the four Cd neighbours

Photo-EPR measurements locate the 0/+ state of VTe at Ev + 0.2 eV and the 2-/- acceptor level of VCd to be situated less than 0.47 eV above the valence band.

Cd0.91Zn0.09Te/CdTe multilayers of various period thicknesses were inserted into Cd0.955Zn0.045Te bulk alloys grown on (001) GaAs. The net strain of the multilayer on the underlying Cd0.955Zn0.045Te was designed to be zero. X-ray diffraction full width at half maximum (FWHM) was used as a means to optimize the period thickness of the multilayer. Transmission electron microscopy of the optimum period thickness samples demonstrated four orders of magnitude decrease in the threading dislocation density. Mechanism of bending by equi-strained multilayers is discussed.

Epitaxial films of ZnTe(100) and CdZnTe(100)/ZnTe(100) have been deposited by molecular-beam epitaxy onto Si(100) substrates misoriented from 0–8 degrees towards the [011] direction. The films were characterized with x ray diffraction, photoluminescence spectroscopy, optical microscopy, and stylus profilometry. Through use of ZnTe buffer layers, single crystal CdZnTe(100) films have been demonstrated on both 4° and 8° misoriented Si with structural quality comparable to that obtained with GaAs/Si composite substrates. X ray rocking curves for ZnTe(400) with FWHM less than 300 arcseconds and for CdZnTe(400) with FWHM less than 160 arcseconds have been obtained for as-grown films. 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 × 106 cm−2 have been deposited by liquid phase epitaxy on these MBE CdZnTe/ZnTe/Si substrates.

(111) wafers sliced from a boule of ZnTe grown by horizontal physical vapor transport (PVT) have been characterized using synchrotron white beam X-ray topography. The growth axis was about 6° off [311]. The presence of dislocation slip bands, subgrain structures and [111] axis 180° rotational twins were revealed. The slip bands were observed to break up the ordered dislocation cell structures comprising the subgrain boundaries. The initiation of slip at regions of stress concentration at the junctions of subgrain boundaries and twin boundaries was observed. The asymmetric distribution of slip bands either side of the twinned region of crystal suggests that twin boundaries can act as barriers for slip. Several types of detailed twin boundary configuration were determined from the topographs. Using a combination of white beam X-ray topography and Nomarski interference microscopy, the three dimensional shapes of the twin boundaries were determined. Approximate atomic structures at these boundaries are presented.

The properties of Cadmium Telluride are very sensitive to impurities. The growth method has also a strong impact on the material characteristics. Crystals grown by THM have good X-ray detector properties, while normal undoped Bridgman grown crystals do not detect. We have grown pure and doped samples by Bridgman and THM methods. As doping materials we used V, Zn and Cl, also in different combinations. The samples were characterized by several methods, including resistivity, TSC and nuclear detection measurements.

Radiation detector grade CdTe crystals are characterized by several crystallographic and metallurgical techniques including infrared microscopy, dislocation etch pitting and X-ray diffraction. Results are presented for 50 detectors fabricated from an ingot produced by the high pressure Bridgman method. Data on the temperature dependence of leakage current and pulse height analysis are presented, along with measurements of room temperature charge transport properties. Attempts to relate crystal structure to detector performance will be discussed.

We present a brief review of results concerning the doping or compensation of CdTe by different elements like halogen, group IV, hydrogen and 3d transition elements for high resistivity materials. Comparison with theoretical models and discussion of results under this light is provided.

The performance characteristics of a linear array composed of several hundred miniature spectroscopy grade CdTe detectors are described. The linear array is utilized in a X-ray security imaging system. It operates either in an energy dispersive mode to highlight certain atomic elements in the luggage or in a regular mode for obtaining only the transmission image of the luggage. The array functions in the photon counting mode and tolerates count rates as high as 106 counts/sec. The array has high quantum efficiency and good spatial resolution which result in excellent image quality. The dynamic range, the electronic noise, the energy resolution, the homogeneity of response among detectors and the image quality are presented.

Results of a program to improve the performance of Cd1−xZnxTe detectors by adjusting growth parameters to achieve low-strain, high purity low defect crystals, investigating surface effect phenomena and contacting methods, and establishing reproducible manufacturing methods are reviewed and discussed. Processing and fabrication methods were developed which are applicable throughout the composition range. Energy spectra for room temperature Cd1−xZnxTe detectors exhibit resolutions (FWHM) from 2.16 keV at 14 keV to 6.9 keV at 122 keV. An energy resolution of 910 eV at 5.9 keV was achieved at −25 C. Stable ohmic contacts and gamma ray detection for ZnTe are reported for the first time. Applications of Cd1−xZnxTe to nuclear medicine and X-ray fluorescence are discussed. New gamma ray imagers using Cd1-−ZnxTe detector arrays are described, and imaging data for a 32 × 32 monolithic array of 1 mm2 elements on a 42mm × 42mm substrate are presented.

The use of cadmium telluride (CdTe) semiconductor nuclear detectors is continuing to expand into new areas because of their unique properties which include room temperature operation and high detection efficiency. In addition, they remain the material of choice in many critical applications such as nuclear medicine and power plant monitoring because of their reputation for reliability and long term stability1. CdTe is by far the most developed of the compound semiconductors used in nuclear detector applications and it offers a number of significant benefits to researchers, clinicians and engineers who have special requirements relating to size, sensitivity and operating temperature.

Recently, there have been improvements in the growth of the crystalline material and in the fabrication procedures which have resulted in better performance and in the ability to produce arrays. This article describes the physical and electronic properties of CdTe nuclear detectors, discusses how the crystal growth and device fabrication procedures can affect these properties, and compares the performance to CdZnTe detectors.

Doped GexSi1−x/Si multiple quantum well structures have been grown by UHV/CVD and characterized by various techniques. SIMS and X- ray confirm the intended modulation of germanium and boron concentrations, and photoluminescence has been used to assess material quality. Strong free- carrier absorption has been observed at normal incidence in some samples. The results suggest that doping intermediate between 4 × 1018 cm−3 and 4 × 1019 cm−3 is necessary for useful detectors.

The theory of multiple quantum well n-type Si-SiGe IR detectors is presented. The coefficient of photoabsorption, quantum efficiency and responsivity of Si-SiGe quantum well detector are calculated taking in consideration the effects of depolarization and electron-electron exchange interaction. We show that the Si-SiGe quantum well detectors possess lower dark current and better performance characteristics compared to GaAs-AlGaAs photodetectors.

Epitaxial narrow gap IV-VI layers on Si-substrates offer an alternate to Hg1−xCdxTe for IR-focal plane arrays with similar ultimate sensitivities. We report on the following improvements in reaching the goal of an easily producible fully monolithic IV-VI-on-active-Si IRFPA: (1) Up to now, compatibility with the Si-substrate was reached through use of a stacked CaF2/BaF2 buffer layer. This layer is replaced by a very thin CaF2 buffer only, which is more suitable for photolithographic processing. (2) Fine resolution wet etching of the IV-VI layers is much easier and reproducible with this new type of buffer. (3) Good homogeneity of cut-off wavelengths is obtained: For a 12 mm long linear Pb1−xSnxSe array with 10.2 μm cut-off wavelength at 95K, the variation in cut-off is smaller than 0.1 μm. (4) The thermal mismatch strain relaxes by dislocation glide even at cryogenic temperatures and after many thermal cycles.

The photoconductive (PC) properties of MBE grown PbTe/Pb1−xEuxTe (x<6.7%) and of PbSe/Pb1−xMnxSe (x<3%) multi quantum (MQW) well samples were investigated in the midinfrared region from 100 meV to 500 meV in the temperature range from 5 K up to 210 K. Whereas in PbTe/Pb1−xEuxTe MQW's electrons and holes are confined in the PbTe layers, PbSe/Pb1−xMnxSe forms a staggered system with electrons confined in the PbSe/Pb1−xMnxSe layers and holes confined in the PbSe layers. Consequently, the transitions between electric subbands in the PbTe/Pb1−xEuxTe MQW's give rise to a step like increase of the PC signal whenever the photon energy hv coincides with the interband transition energies between hole and electron subbands (selection rule Δn = 0). For the range of well widths investigated (42 Å to 91 Å ) distinctive steps in the photoconductivity spectra were observed. In the PbSe/Pb1−xMnxSe MQW's the absorption signals show a typical type II superlattice (SL) behaviour and thus the photoconductivity response is also much weaker than for the PbTe/Pb1−xEuxTe MQW's.

Ferroelectrics such as PbTiO3 and BaSrTiO3 are promising candidates for pyroelectric infrared detector materials. Integration of ferroelectric thin films on Si will permit fabrication of low-cost infrared detector arrays, but a buffer layer will be required to reduce interactions with the substrate. For this reason we have investigated MOCVD of MgAl2O4 and yttria-stabilized zirconia (YSZ) buffer layers on both Si and MgO. A single source molecule, magnesium dialuminum isopropoxide (Mg[Al(OCH(CH3)2)4]2), was used for deposition of the MgAl2O4, the first time to our knowledge that well characterized multi-metal oxide films have been deposited by CVD from a single-source compound. Both EDAX and RBS showed film stoichiometries consistent with the elemental ratio in the source. A novel liquid solution-based flash vaporization technique was used to transport the organometallic sources into the reactor, providing both excellent reproducibility and ease of stoichiometry control and deposition rate. Highly oriented [100] MgAl2O4 was grown on MgO, and [100] YSZ was grown on MgO and Si. Degree of preferred orientation of the YSZ was found to be dependent on oxygen partial pressure, both for the MgO and Si substrates.

The thermal analysis on the response of pyroelectric detector revealed that an optimal configuration structure could be found for a certain frequency range. Thus, it appeared that the pyroelectric layer should be thick at low frequencies but it should be very thin at high frequencies. The introduction of a thermal insulator is done trying to find out a trade off between sensitivity and response time. It has been found that its influence is restricted to a certain frequency range. The optimal thickness is related to the thermal diffusion length. We noticed also that it depends very little on the configuration structure.