Thick layers were deposited onto Al2O3 (00•1) substrates by using hydride vapour phase epitaxy, while modulating the growth. Cathodoluminescence and transmission electron microscopic images of the cross-sectional structure showed that there were separate multi-layers in the films. The dislocation density decreased from 1010/cm2 in the initial layer, to between 109 and 108/cm2 in the subsequently grown layer, and then to 107/cm2 in the top layer. This showed that interruption of the growth process helped to suppress structural defects.

Dislocation Reduction in GaN Grown by Hydride Vapour Phase Epitaxy via Growth Interruption Modulation. W.Zhang, S.Roesel, H.R.Alves, D.Meister, W.Kriegseis, D.M.Hofmann, B.K.Meyer, T.Riemann, P.Veit, J.Blaesing, A.Krost, J.Christen: Applied Physics Letters, 2001, 78[6], 772-4