Epitaxial growth of nonpolar and polar ZnO on γ-LiAlO_2 (100) substrate by plasma-assisted molecular beam epitaxy

摘要

Low lattice mismatched γ-LiAlO_2 (100) substrates were employed for the epitaxial growth of ZnO by plasma-assisted molecular beam epitaxy. The crystallographic orientations of the samples were determined by the X-ray diffraction (XRD) patterns. The surface morphology and roughness of ZnO films were investigated by scanning electronic microscopy (SEM) and atomic force microscopy (AFM). Results confirmed that both nonpolar (1010)- and polar (0001 )-oriented ZnO epilayers can be grown, demonstrating the dual orientation-selection characteristic of the γ-LiAlO_2 substrate. The growth temperature and grow rate are two major factor which affects the orientation competition. A two-step growth method was therefore designed to improve the quality of the polar ZnO film grown at high temperature. Room temperature photoluminescence spectra of both polar and nonpolar ZnO films showed a near band edge emission peak at around 377 nm and a negligible green band emission.