The effect of high-temperature buffer layers on the structural characteristics of GaN grown, using hydride vapour-phase epitaxy, onto sapphire was investigated. Strain relaxation as well as mismatch-induced defect reduction in thick GaN layers grown on an AlN buffer was identified microscopically by applying cathodoluminescence and micro-Raman spectroscopy to cross-sections of the films. The results were correlated with photoluminescence and Hall-effect data for layers with various thicknesses. These relaxation processes were suggested to account for the specific defect distributions in the buffers, as revealed by high-resolution X-ray diffraction and transmission electron microscopy.

Defect and Stress Relaxation in HVPE-GaN Films using High-Temperature Reactively Sputtered AlN Buffer. T.Paskova, E.Valcheva, J.Birch, S.Tungasmita, P.O.Å.Persson, P.P.Paskov, S.Evtimova, M.Abrashev, B.Monemar: Journal of Crystal Growth, 2001, 230[3-4], 381-6