THERMAL VIBRATIONAL AMPLITUDES OF CONSTITUENT ATOMS AND MECHANICAL STABILITY IN ZNXCD1-XTE AND HG1-YCDYTE

Root-mean-square (rms) displacements of the constituent atoms in the ZnxCd1-xTe (x =0,0.04,0.077,0.114,0.20,0.31) and Hg1-yCdyTe (y =0,0.24,0.4,0.7) alloys are determined by ion channeling experiments combined with particle-induced x-ray emission and Rutherford backscattering. The experimental channeling angular scan data are interpreted by using a recently developed method, which uses a Monte Carlo simulation program of the channeling process, and includes a structural model for the ternary alloys based on extended x-ray-absorption fine-structure results on nearest-neighbor distances. Temperature-dependent measurements show that the experimentally deduced atomic displacements do not contain static contributions but they are rather due to the thermal vibrational amplitudes of the atoms. The room-temperature results are found to be in general agreement with the few thermal amplitude data reported in the literature obtained by other experimental methods. For both ZnxCd1-xTe and Hg1-yCdyTe the rms displacements change nonmonotonically with composition. In some cases, the results are found to correlate with the experimentally determined bulk moduli and microhardness. The above correlations deduced from the present experiment for Hg1-yCdyTe and ZnxCd1-xTe are found to be common to other tetrahedrally bonded semiconductors. Temperature-dependent results for ZnxCd1-xTe crystals which show a strong reduction in thermal amplitudes as compared to CdTe at room temperature reveal deviations from the Debye behavior, not observed for the other materials studied. Possible explanations for the effects observed, as well as their implications to the phonon-dispersion relations of the ternary alloys studied, are discussed in detail.