Effect of the growth temperature on the properties of Al _xGa _l-xN epilayers grown by HVPE

Growth of the Al _xGa _1-xN ternary alloy using AlCl ₃ and GaCl gases on sapphire substrate by hydride vapor phase epitaxy (HVPE) is presented in this study. Al _xGa _1-xN epilayers were grown directly on sapphire substrate. To investigate the effect of growth temperature, we varied temperature from 1050 to 1090 °C at intervals of 20 °C. Some compositional non-uniformity was observed on the epilayer grown at 1050 °C from the results of UV-vis spectrophotometry, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Such a compositional non-uniformity disappeared with the increase of growth temperature and it was confirmed with the existence of Ga-rich islands shown by electron probe microanalysis (EPMA) compositional mapping. In addition, other characteristics such as surface roughness and crystallinity also improved with the increase of growth temperature and showed best results at 1090 °C. The Al composition of epilayer grown at 1090 °C was around 30%.