Substrate-orientation dependence of <i>β</i>-Ga2O3 nitridation by RF nitrogen plasma for GaN heterojunction diodes

The influence of substrate orientation on the structural properties of heteroepitaxial GaN films grown on nitridated β-Ga2O3 (BGO) is investigated. The nitridation of (100), (001), and (2¯01) β-Ga2O3 was monitored with reflection high energy electron diffraction and x-ray photoelectron spectroscopy, suggesting the reaction proceeds through the formation of an oxynitride phase in all cases. The nitridation rate (Γ) under fixed nitridation conditions was observed to increase monotonically with the inverse of the surface free energy of the starting substrate, Γ(001) &amp;lt; Γ(2¯01) &amp;lt; Γ(100). Hexagonal GaN is realized on all orientations, however, (001) BGO nucleates an undesired (101) plane GaN interface. The presence of restructured BGO grains is also observed on (100) BGO. Analysis of XRD pole figures suggests that twinned lamellae are not translated into the GaN epitaxy after nitridation of (2¯01) or (100), though may be present when grown on (001), attributed to large misfit strain in this orientation. Mg:GaN grown on (2¯01) BGO retained p-type conductivity and low FHWM of the 0002 x-ray rocking curve, indicating (2¯01) BGO being the most conducive of the tested interfaces for GaN heteroepitaxial device fabrication.