We have studied at cryogenic temperatures photoluminescence features which lie more than 0.15 eV below the band edge in Zn Cd& Te (0+x 0.09) crystals. The same features, namely a defect band which lies at about 0.13 -0.20 eV below the band-gap energy and a peak at 1.1 eV, that are observed in pure CdTe samples are observed in these alloy materials. In annealed samples we observe that the 1.1-eV feature, which has been attributed to tellurium vacancies, increases with fast cooling. Increased concentrations of tellurium vacancies can be understood in terms of the phase diagram of CdTe which indicates that higher concentrations of excess Cd appear in CdTe quenched from high temperatures. We also observe an absorption transition near 1.1 eV by photothermal deflection spectroscopy (PTDS). The PTDS phase shifts show that the deep defect is a bulk effect rather than a surface effect. The welldefined absorption peak suggests that the states contributing to the 1.1-eV transition are both localized.Our results also suggest that the defect band which lies 0.13 eV below the band gap (1.48 eV in CdTe) may also be related to tellurium vacancies. However, the fact that the ratio of intensities between this defect band and the 1.1-eV feature is highly variable suggests that the relationship is not simple. The origin of the defect band and its phonon replicas remains controversial.
The crystalline quality of ZnxCd1−xTe single crystals prepared by a modified Bridgman method with 0≤x≤0.05 has been analyzed using photoluminescence. The spectrum of a typical sample is dominated by lines originating from the recombination of free and bound excitons. Lines due to free excitons in their ground and first excited states are observed in both the pure CdTe and the mixed crystals. Excitons bound to Cd vacancies are observed in the pure CdTe crystal but not in the mixed crystal. Weaker and broader features appearing at energies below the exciton emission range were associated with transitions involving free-to-bound and bound-to-bound levels. The origin of the various lines in the spectra was deduced from the detailed measurements of the dependence of the spectrum on temperature and excitation intensity.
The anisotropic segregation of Se in normalInSb has been studied using radioactive Se as a tracer element. A core consisting of a high concentration of Se has been found in the center of crystals pulled in the [111] direction. This phenomenon is thought to result from an extremely rapid lateral growth occurring on the (111) facet. Well‐defined striations were also observed. Crystals grown from seeds oriented in directions other than the [111] are found to have high concentrations of Se in the (111) facets near the edge of the crystal, thus removal of the edges leaves the major portion of the crystal relatively homogeneous and with lower impurity content.
Two infrared absorption bands attributed to substitutional boron-phosphorus pairs in silicon are observed. The bands are close to the single, isolated boron band and all show approximately the same frequency shift with change in boron isotope. The pair bands occur near 599.7 and 629 cm−1 for 11B and 622.9 and ∼655 cm−1 for 10B. The results are compared with the theory of Elliott and Pfeuty. The number of pair bands, their isotope shift, and their proximity to the isolated B band are in agreement with theory. The Δν ∼ 30 cm−1 is an order of magnitude larger than predicted by the isotopic model indicating changes in force constants.
Silicon is known to be an amphoteric impurity in GaAs. A large number of ir absorption bands have been previously reported for Si-doped GaAs which has been compensated by Li or Cu diffusion. These bands, which are at frequencies above the pure GaAs single-phonon spectrum, have been attributed to localized vibration modes of defects. The present experimental study extends previous work to show that all the observed bands (frequencies given in parentheses) are explicable in terms of the presence of the following defects: SiGa (384 cm−1), SiAs (399 cm−1) SiGa-LiGa (374, 379, 405, 470, 480, 487 cm−1), SiGa-CuGa (374, 376, 399 cm−1), and SiGa-SiAs. (367, 393, 464 cm−1). These assignments appears to be consistent with results obtained by varying the Si concentration and by different thermal treatments.
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