Crystalline Quality, Composition Homogeneity, Tellurium Precipitates/Inclusions Concentration, Optical Transmission, and Energy Band Gap of Bridgman Grown Single-Crystalline Cd1−xZnxTe (0 ≤ x ≤ 0.1) (original) (raw)
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Improvement in crystalline quality of Cd1−xZnxTe(x=4%) crystals grown in graphite crucible
Journal of Crystal Growth, 2004
In this paper, we report improvement in the crystalline quality of CdZnTe (Zn=4%) crystals, with respect to etch pit density and full-width half-maximum (FWHM) of the X-ray rocking curve, grown in graphite crucible as compared to crystals grown in carbon-coated quartz ampoule. Uniform dislocation density distribution of the order of 2-3  10 4 cm À2 with no cellular structure and improvement in FWHM value (18-30 arcsec) with reduced splitting of peaks in X-ray rocking curves have been observed in the complete cadmium zinc telluride (CZT) wafers (30 mm  50 mm). We have used a larger X-ray beam (10 mm  1 mm) to study the crystalline quality of the complete CZT ingot. The effect of variation of beam size on X-ray rocking curve and its FWHM value indicates that the use of large beam size gives the true assessment of the spatial crystalline perfection of the grown CZT crystals. Although improvement in terms of crystalline perfection has been achieved in CZT material, the fall in optical transmission in the longer wave length spectral region and measured electrical properties in the annealed CZT samples point towards the incorporation of impurities in CZT during growth from the graphite crucible. Our results clearly indicate that overall improvement in the quality of CZT crystal is achievable with the use of ultra-high-purity graphite as the crucible. r
Solid-liquid phase transitions in Cd0.95-xMnxZn0.05Te alloys with x = 0.20 and 0.30 were investigated by differential thermal analysis (DTA). The heating/cooling rates were 5 and 10 K/min with a melt dwell time of 10, 30 and 60 minutes. Cd0.95-xMnxZn0.05Te (x=0.20, 0.30) single-crystal ingots were grown by the vertical Bridgman method guided by the DTA results. Te inclusions (1-20 micron diameter), typical of melt-grown CdTe and Cd(Zn)Te crystals, were observed in the ingots by infrared transmission microscopy. The measured X-ray diffraction patterns showed that all compositions are found to be in a single phase. Using current-voltage (I-V) measurements, the resistivity of the samples from each ingot was estimated to be about 10 5 Ohm•cm. The optical transmission analysis demonstrated that the band-gap of the investigated ingots increased from 1.77 to 1.88 eV with an increase of the MnTe content from 20 to 30 mol. %.
Growth and characterization of Cd1−xZnxTe crystals with high Zn concentrations
Journal of Crystal Growth, 2000
The crystalline quality of large grain size Cd \V Zn V Te with high Zn concentrations (0.45(x(0.85) grown by a zone melting process was investigated using photoluminescence, X-ray di!raction, optical transmission and micro-Raman measurements. We have found that extrinsic and intrinsic factors lead to Zn segregation encountered in both the radial and the longitudinal directions. The degree of segregation depends on the nominal Zn concentration. In addition, small precipitates of tellurium are found in the regions with low Zn concentrations in the solid solution. Such precipitates are absent in regions with high Zn concentrations.
Production of structurally perfect single crystals of CdTe and CdZnTe
The European Physical Journal Applied Physics, 2004
Single-crystal ingots of CdTe and Cd0,96Zn0.04Te 60-100 mm in diameter were grown by directional solidification using the self-seeding technique. The microstructure of the crystals was checked by optical microscopy, electron microscopy (TEM, SEM and EBIC), cathodoluminescence, and X-ray diffraction. It was found that crystal perfection depends to a large measure on the temperature schedule during Lpostgrowth crystal cooling: special caution should be exercised in the temperature interval including the polymorphous transformation. A direct relationship between optical and electronic properties on the one hand and crystal microstructure on the other hand was established.
Journal of Crystal Growth, 1998
In this work the principles of self-selecting vapour growth (SSVG) are described and the advantage of the method in allowing continuous refinement of a crystalline mass is explained. The method's use of low supersaturation and its ability to grow crystals free from the walls of a capsule make the SSVG principle an attractive one for the growth of CdTe and Cd \V Zn V Te boules. Here a new vertical SSVG apparatus was used to grow small crystals of these two materials and the defects in them were characterised by etching and HRXRD. Compositional uniformity of the Cd \V Zn V Te grown was found by PL and HRXRD to vary by not more than 0.0014 in x (i.e. 0.14%). This compares favourably with other vapour growth studies in which low undercooling (¹&1-2°C) was used.
Journal of Crystal Growth, 1993
single crystals grown by vertical Bridgman-Stockbarger technique. A solution of S-7% Br, in methanol and E-solution were both effective. High resolution scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) was employed to characterize those exposed precipitates. Most of the polyhedral-shaped Te precipitates with a size range from 3 to 20 Frn had voids inside. Partially dissolved Te precipitates were observed in CdTe samples that had been annealed in Cd vapor at 700°C for 10 min. Isolated areas mis-oriented from the matrix were observed in CdTe and Cd a.s6Zna,mTe that had been annealed in Cd vapor at 700°C for 20 and 50 h, respectively. Te precipitate images were recorded with EDS. By SEM/EDS, Cd-rich precipitates were observed in some Cd-annealed CdTe. C and Na impurities were detected in some Te precipitates.
Journal of Crystal Growth, 2000
CdTe crystals grown by the Bridgman method were characterized by relating the Te excess to the bulk and their crystalline quality (CQ). The thermal di!usivity of these samples was measured using photoacoustic spectroscopy (PA). X-ray di!raction (XRD) data of the (1 1 1) peak of CdTe was employed to calculate the full-width at half-maximum (FWHM) and the lattice parameter. These results were used to compare CQ of di!erent CdTe samples. The presence of Te inclusions and precipitates in the crystal was evident by XRD measurements and was con"rmed using micro-Raman (R) spectroscopy. R microprobe scanning images were employed to determine the size, morphology, position and density of Te aggregates in the crystals. Photoluminescence (PL) measurements were carried out in order to assess the optical quality of the crystals and to relate these results to the XRD data. According to the experimental data, thermal di!usivity () is higher in samples with high crystalline quality and has strong dependence on the micro-structural composition of Te precipitates and inclusions.
Surface morphology and depth profile study of Cd1-xZnxTe alloy nanostructures
Cd1−xZnxTe thin films with thickness of 200 nm were deposited on glass substrates from a single sputtering target. During the deposition process, the substrates were heated at 400 °C and deposited films were subjected to an annealing process at 300 and 450 °C for an hour under flowing N2 gas at atmospheric pressure. Influence of in situ heating and post-deposition annealing treatments on the structural and optical evolution of Cd1−xZnxTe nanostructures were investigated by diagnostic techniques such as X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and UV-transmission spectroscopy. The transmission spectra in the region of the optical absorption band edge were measured for as-deposited and heat-treated of CdZnTe samples. Band gap of the deposited films were found to be in the range of 1.59–1.66 eV. The XRD studies revealed that heated Cd1−xZnxTe films have a cubic oriented (1 1 1), (2 2 0) and (3 1 1) polycrystalline structure whereas unheated films are mostly amorphous. The effects of annealing temperature on the composition of the thin films were discussed. XPS measurements were performed in the depth profiling mode in order to understand the variation in the chemical composition of the films. Results were compared with the structural analysis obtained from the XRD measurements.► Cd1−xZnxTe (CZT) films were grown on heated glass at 400 °C from a single target. ► CZT films were annealed at 300 and 450 °C for 1 h under N2 gas at atm. pressure. ► The structural and optical properties of CZT films were studied. ► Better structural stability and reproducibility in CZT films were succeeded. ► Uniform and stoichiometric CZT films with required compositions were fabricated.
2001
Characterization studies of Cd 1−x Zn x Te (0<x<0.24) crystals, CZT, grown by high pressure vertical Bridgman (HPVB), low pressure (LPB) vertical modified Bridgman (VB), horizontal modified Bridgman (HB), and physical vapor deposition (PVD) methods were performed. For selected melt-grown ingots, the liquid/solid segregation coefficients of some of the impurities were established. For most of the crystals, the surface and the bulk crystallinity were determined using triple and double axis X-ray diffraction techniques (TAD and DAD XRD).