University of Science and Technology Beijing,School of Mathematics and Physics,Department of applied physics
Polycrystalline gallium nitride (GaN) thin films were deposited at low temperatures on GaAs (001) substrates via plasma-enhanced atomic layer deposition (PEALD). The growth process, surface mechanism and interface characteristics were investigated. The results showed that the PEALD temperature window was 215~270℃, and the average growth rate of GaN thin films was 0.82?/cycle. The GPC analysis was performed in terms of kinetic energy barriers and thermodynamics. X-ray diffraction (XRD) patterns indicate that the GaN thin films are polycrystalline with hexagonal wurtzite structure and have a tendency to form (103) preferential orientation. With High-resolution transmission electron microscopy (HRTEM), the atomic steps on the mitered substrate surface and the presence of an amorphous layer of about 1 nm at the GaN/GaAs interface are easily observed. This may be related to the surface concentration of active sites and the steric effect of the adsorbed precursor fragments. Most interestingly, X-ray photoelectron spectroscopy (XPS) analysis shown that all N elements combine with Ga elements to form GaN by Ga-N bond, but a small part of Ga formed Ga-Ga bonds and Ga-O bonds. This bonding method during deposition may be related to the defects and impurities in the GaN thin films.