Crystalline phase purity and twinning of Mg-doped zincblende GaN thin films

Abstract

Zincblende (zb) GaN thin films doped with Mg were grown by molecular beam epitaxy on GaAs under Ga- and N-rich conditions and different Mg cell temperatures. X-ray diffraction and electron-backscatter diffraction determined the ideal orientation of the zb-GaN, its textural relationship to the substrate, wurtzite and twin content, and their interfaces with the GaN matrix. A comparison to pole figure simulations allowed a thorough description of orientation of wurtzite inclusions and twins, forming interfaces along the 〈111〉 directions of the matrix. The results revealed zincblende volumetric purities as high as 99.9 % and twinning as low as 1.3 %. Ga-rich conditions and lower doping cell temperatures led to the highest phase purities. Moreover, crystalline and surface quality are also deeply linked to the wurtzite inclusions and twinning obtained. Films with the least amounts of these displayed the highest quality. This is likely due to excess Ga atoms on the surface helping the Mg doping atoms incorporate more orderly into the growing film. The results from this investigation provide a deeper understanding of the effects of Mg doping on the crystalline structure of zb-GaN films, paving the way for practical applications of zincblende nitrides in modern optoelectronic devices.