The effect of nitrogen pressure on the two-step method deposition of GaN films

Abstract

GaN thin films were deposited on sapphire (0001) substrates at different nitrogen pressures by pulsed laser deposition (PLD) of GaN target in nitrogen atmosphere. Good single crystal GaN thin films were obtained after annealing at 1000 °C for 15 min in a NH3 atmosphere. An Nd:YAG pulsed laser with a wavelength of 1064 nm was used as the laser source. The influence of nitrogen pressure on the thickness, crystallinity and surface morphology of GaN films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and Raman spectroscopy. The results show that at low nitrogen pressure, the surface diffusion of adatoms can be influenced by the collisions between the nitrogen gas molecules and the activated atoms, which can influence the kinetic energy of the activated atoms. However, at high nitrogen pressure, the kinetic energy of adatoms is decided by the annealing temperature. In our experimental conditions, the GaN thin films deposited at 0.75 and 7.5 Pa have a high surface morphology and crystalline quality.