Investigations on band commutativity at all oxide p-type NiO/n-type β-Ga2O3 heterojunction using photoelectron spectroscopy

Epitaxial growth of (111) oriented NiO layers on (-201) oriented beta-Ga2O3 and vice versa have been carried out to obtain an all oxide p-n heterojunction (HJ) consisting of NiO/beta-Ga2O3 and beta-Ga2O3/NiO interfaces, respectively. Careful investigations by minimizing the effect of differential charging phenomena during x-ray photoelectron spectroscopy measurements yield a valence band offset (VBO) value of 1.6 +/- 0.2 eV for both NiO/beta-Ga2O3 and beta-Ga2O3/NiO HJs. Thus, the VBO value is practically independent of the growth sequence for p-type NiO/n-type beta-Ga2O3 HJs and follows band commutativity. The band diagram shows a staggered (type-II) band alignment and the value of the conduction band offset is found to be small (0.3 +/- 0.2 eV). Our results are useful to design optoelectronic devices based on all oxide p-type NiO/n-type beta-Ga2O3 HJs.