NEAR-BAND-EDGE OPTICAL-PROPERTIES OF MOLECULAR-BEAM EPITAXY-GROWN ZNSE EPILAYERS ON GAAS BY MODULATION SPECTROSCOPY

A study of near-band-edge optical properties of ZnSe epilayers grown o n GaAs substrates using various modulation techniques is presented. We compare the contactless electroreflectance (CER) and piezoreflectance spectra to ascertain that our ZnSe epilayers of 1.2 mu m in thickness grown on GaAs substrates are under a biaxial tensile strain. The defe ct-related transitions near the ZnSe/GaAs interface are also compared by identifying the photoreflectance and other spectra, In addition, in order to observe the temperature-dependent energy splitting and strai ns, we present a detailed investigation of the heavy-hole and light-ho le related transition energies as a function of temperature in the 15- 200 K range by identifying the excitonic signatures in the CER spectra . We have also calculated the energy splitting between heavy-hole and light-hole valence hands by utilizing the temperature-dependent elasti c constants for ZnSe and the thermal expansion coefficients for ZnSe a nd GaAs. Both the experimental result and the theoretical calculation have shown a similar trend that the biaxial tensile strains decrease i n magnitude with increasing temperatures in the 1.2 mu m ZnSe epilayer grown on a GaAs substrate. (C) 1998 American Institute of Physics, [S 0021-8979(98)02803-5].