Hydride vapour phase epitaxy growth and characterization of GaN layers

A vertical hydride vapour phase epitaxial reactor was applied for the growth of GaN layers on (0001) sapphire. In this paper, the growth parameters and the results of optical investigations are reported. It is seen that the layers grown at high temperature have better crystallographic properties than those grown at 600-800 °C, although the latter show a smoother surface. The absorption spectra exhibited a tail from the absorption edge down to about 1 eV that may be fitted by the Lukovsky model considering the presence of a level at about 1.2 eV from the conduction band. The cathodoluminescence spectra show three main emissions: the yellow band, a blue band (BB) centred at 2.8 eV and the near band edge recombination. The BB is mostly originated close to the layer/substrate interface and practically extinguished at the layer surface. It is seen that when the intensity of the BB increases that of the fundamental recombination decreases and vice versa.