A New Method for A Great Reduction of Dislocation Density in A GaN Layer Grown on A Sapphire Substrate

A new method to reduce the dislocation density in a GaN film grown on sapphire substrate by metalorganic chemical vapor deposition (MOCVD) is reported. In this new method, SiH4 and NH3 gases are simultaneously introduced at a low temperature with a certain time before the growth of an initial low-temperature GaN buffer layer. By transmission electron microscope (TEM), the density of threading dislocation originating from the interface between low-temperature buffer layer and high-temperature GaN layer decreases to be almost invisible from 7×108/cm² in the conventional MOCVD growth technology for GaN film. Atomic force microscopy indicates that introducing SiH4 and NH3 gases at a low temperature changes surface morphology, which probably enhances the lateral growth and then decreases the dislocation density. This method could be used for fabrication of long-lifetime GaN-based laser instead of epitaxial lateral overgrowth.

N hydride vapor phase epitaxial (HVPE) growth of GaN, the sputtered ZnO layer has been found to be one of the best buffer layers because of the fact that physical properties of ZnO are nearly analogous with those of GaN. With a ZnO buffer layer, the reproducibility of growing GaN single crystal by HVPE has been greatly improved. The GaN films grown by this method show excellent crystalline, electrical, and optical properties. In particular, the Hall mobility of 1920 cm² V-1 s-1 at 120 K is the highest value that has ever been reported by HVPE.


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