Effects of ZnO buffer layers on the fabrication of GaN films using pulsed laser deposition

摘要

GaN thin films were deposited on Si (111) substrates using ZnO buffer layers by pulsed laser deposition of a GaN target in a nitrogen atmosphere. High-quality GaN thin films were obtained after annealing at 950℃ for 15 min in a NH_3 atmosphere. The crystalline quality, composition, and surface morphology of the films were characterized by x-ray diffraction, Fourier transform infrared spectroscopy, and atomic force microscopy. Through analysis of the measured results, a conclusion was drawn that ZnO buffer layers and their crystalline quality affected the structural properties (crystalline quality, composition, and surface morphology) of GaN films. Crystalline ZnO buffer layers improved nucleation and growth of GaN films. Zn-O bonds are destroyed when the GaN films are annealed in ammonia (NH_3) ambience; a few O and Zn atoms depart from their positions, while N and Ga atoms fill in the empty positions and form a hexagonal structure of a special component. The structure is propitious to the epitaxial growth of GaN, while the motion of atoms gives the grains of GaN more chances to move and form Ga-N bonds. The annealing time markedly affects the preparation of GaN films and the least annealing time is 15 min under our experimental conditions.