A new method for reducing the dislocation density in films grown on sapphire by means of metal-organic chemical vapour deposition was reported. In this method, SiH4 and NH3 were simultaneously introduced, at a low temperature, some time before the growth of an initial low-temperature nitride buffer layer. Transmission electron microscopy showed that the density of threading dislocations which originated from the interface between the low-temperature buffer layer and a high-temperature nitride layer decreased to apparently zero, from the 7 x 108/cm2 found when using conventional growth technology. Atomic force microscopy data indicated that introducing SiH4 and NH3 at a low temperature changed the surface morphology. This probably enhanced lateral growth, and thus decreased the dislocation density.
A New Method for a Great Reduction of Dislocation Density in a GaN Layer Grown on a Sapphire Substrate T.Wang, Y.Morishima, N.Naoi, S.Sakai: Journal of Crystal Growth, 2000, 213[1-2], 188-92