Structural properties of ZnSe epilayers on (111) GaAs

Structural and optical studies of ZnSe epilayers, which were grown on the B side of (111)-oriented GaAs substrates, indicate the presence of tensile in-plane strains in the epilayers at room temperature. Electron microscopy observations showed that the ZnSe epilayer forms a coherent sharp interface with the GaAs substrate and consists of crystallites which are grown in epitaxial or twin orientation with respect to the substrate, having the (111) planes oriented parallel to the interface. In addition, embedded twins are observed within the epilayer. The twin boundaries are, generally, terminated by Shockley partial dislocations, which are expected to relax the compressive lattice mismatch strain. Plastic or thermal relaxation cannot account for sign and magnitude of the observed strains. Evidence is found that the observed tensile strains are piezoelectrically induced in a depletion layer, due to Fermi level pinning at the ZnSe/GaAs interface.