The structural and optical properties of high quality ZnTe grown on GaAs using ZnSe/ZnTe strained superlattices buffer layer

This work studied the structural and optical properties of ZnTe epilayers grown on GaAs substrates with ZnSe/ZnTe strained superlattices buffer layers. Material properties were characterized using cross-sectional transmission electron microscopy, photoluminescence (PL), contactless electroreflectance (CER), and piezoreflectance (PzR). PL spectra clearly distinguished the strong free exciton peaks, weak donor-acceptor pair, Y lines, and oxygen-bound exciton peaks, indicating the high quality of the films. In addition, the CER and PzR spectra were compared to ascertain that ZnTe epilayers of 1.5 mu m in thickness grown on GaAs substrates are under a biaxial tensile strain. An attempt was also made to identify the origins of the near-band-edge transitions of ZnTe epilayer in the CER and PzR spectra by comparing these spectra with PL spectra and the second harmonic frequency CER. By doing so, the interference below the band gap of ZnTe could be effectively eliminated. Moreover, the energy splitting between heavy- and light-hole valence bands at 15 K was calculated by utilizing the temperature-dependent elastic constants for ZnTe and the thermal-expansion coefficients for ZnTe and GaAs. The discrepancy between experiment and calculation indicates that the residual mismatch-induced strain and the thermally induced strain in ZnTe epilayers grown on GaAs during cooling must be simultaneously considered. (C) 1998 American Institute of Physics. [S0021-8979(98)05217-7].