Buffer layer ZnO-assistant fabrication of c-axis GaN films by using pulsed laser deposition on Si(111) substrate: annealing effects in ammonia ambience

ZnO buffer layers have been used to fabricate GaN thin films by using pulsed laser deposition on Si (111) substrates. c-axis GaN thin films were obtained by annealing in NH3 atmosphere at 950°C for 15 min. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM) have been used for the characterizations of the crystalline quality, composition, and surface morphology of the films. The annealing in ammonia (NH3) atmosphere markedly affects the preparation of GaN films and the least annealing time is 15 min under our experimental conditions. The mechanism of the effects of the ZnO buffer layers was studied. In the beginning, Zn–O bonds are destroyed in the interface of the films; 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. Many bonds (such as Ga–O bonds, Zn–N bonds) existed then. The number of Zn–O bonds decreases and the number of Ga–N bonds increases in the films with increasing of the annealing time. Many other bonds (such as Ga–O bonds, Zn–N bonds) also decreased and more Ga–N bonds formed with annealing time increasing. After having been annealed for 15 min under our experimental conditions, the quality of the hexagonal structure GaN films was markedly improved by the destroying of the Zn–O bonds during high-temperature annealing.