Effect of A1N buffer layer on the microstructure and bandgap of A1N films deposited on sapphire substrates by pulsed laser deposition

摘要

A1N buffer layer is proposed to improve the growth of A1N films on the sapphire substrate by pulsed laser deposition. The buffer layers were pre-deposited under vacuum for different time, which was aimed to suppress the negative nitridation effect in the initial growth stage, and their effects on the surface morphology, crystal structure and bandgap of A1N films were characterized. It is found that AIN-buffered films exhibit a single (0002) preferred orientation and the crystallinity improves as the pre-deposition time increases from 5 to 20 min. Al-polarity A1N films are obtained at the pre-deposition time of 5 and 10 min, while the polarity inversion from the Al- to N-polarity is observed at 20 min. Based on the analysis of optical transmittance spectra, the bandgap of A1N films decreases with increasing pre-deposition time, which may be resulted from the decrease of axial ratio cla.