THERMAL-EXPANSION ANISOTROPY IN THE QUATERNARY SEMICONDUCTOR CUGAGE1-X(VGE)XSE4 AT ELEVATED-TEMPERATURES

Accurate lattice parameters a and c of the quaternary tetragonal- chalcopyrite-type semiconductor CuGaGe1-x(VGe)xSe4 have been determined as a function of temperature by the x-ray powder-diffraction method in the temperature range 300664 K. The data have been used to evaluate the axial-thermal-expansion coefficients a and c at various temperatures. The thermal-expansion studies revealed the anisotropy between the axial-expansion coefficients having a larger coefficient of expansion along the a axis than that along the c axis (i.e., a>c). The mean values of a and c in the temperature range studied are found to be 20×10-6 and 9.13×10-6 K-1, respectively, and the axial ratio c/a changes with a coefficient of -10.98×10-6 K-1. This result indicates an increase in the tetragonal distortion (=2-c/a) of the chalcopyrite structure with increasing temperature. An attempt is made to explain the increase in the tetragonal distortion with temperature and the anisotropic thermal expansivity of CuGaGe1-x(VGe)xSe4 in terms of the thermal expansion of the AI,III-Se (where AI,III is Cu and Ga randomly distributed) and BIV-Se [where BIV is Ge and vacancy (VGe) randomly distributed] bonds. The results are compared with thermal-expansivity data for other quaternary chalcopyrite-type semiconductors and are discussed in terms of the principal Gr̈neisen parameters of these compounds. © 1990 The American Physical Society.