LP-MOCVD growth of GaN on silicon substrates—comparison between AlAs and ZnO nucleation layers

Abstract

The impact of AlAs and ZnO nucleation layers on the low-pressure MOCVD growth of GaN on silicon substrates is the subject of this study. In both cases, prior to the high-temperature deposition of the GaN main layer a thin low-temperature GaN buffer layer has been found to improve the crystal quality. Especially in the case of a ZnO nucleation layer, no single crystalline growth of GaN was obtained without a low-temperature GaN buffer layer. Furthermore, the crystallographic quality of the GaN layer is strongly dependent on the strength of the (0001) texture of the ZnO grains. The ZnO (0001)-texture is independent of the Si(111) or Si(001) orientation and allows for single crystalline growth of GaN on both types of Si surfaces. TEM investigations show, that the ZnO nucleation layer has completely vanished after the epitaxial process. In contrast, AlAs nucleation layers remain stable as proven by X-ray diffraction and TEM measurements.