GaN films grown on (0 0 1) and (1 1 0) MgF2 substrates by plasma-assisted molecular beam epitaxy (PA-MBE)

Abstract

The growth of gallium nitride (GaN) on magnesium fluoride (MgF2) by plasma-assisted molecular beam epitaxy (PA-MBE) was investigated under different conditions. GaN films on MgF2 substrates are a promising material combination for UV-detectors in space applications. Two different crystallographic orientations of MgF2 were used to analyse the influence on the formation of GaN. The GaN layers on (0 0 1) MgF2 had better quality in comparison to a (1 1 0) surface orientation. Under a high Ga flow only cubic β-GaN without hexagonal α-GaN was formed at the growth on (0 0 1) MgF2. The layers, grown under other conditions, consisted mainly of the meta-stable cubic GaN with inclusions of the hexagonal phase. With higher substrate temperatures a rougher surface and a higher grain size could be observed. The best results were obtained with a substrate temperature of 450 °C and a prior wetting of the surface with only gallium. In this case the relative low substrate temperature could be compensated. In X-ray diffraction (XRD) analysis mainly (1 1 1), (2 2 2) and (2 2 0) peaks were observed indicating that mostly cubic GaN was present.