Fabrication and Interfacial Electronic Structure of Wide Bandgap NiO and Ga₂O₃ p–n Heterojunction

Ga2O3 is emerging as an interesting semiconductor for high-power electronics and solar-blind ultraviolet photodetectors because of its ultrawide bandgap and high breakdown field. To fully extend its applications in optoelectronics, it is highly desirable to fabricate a p–n heterojunction. In this work, we report detailed investigations on the epitaxial growth and interface properties of a p–n heterojunction consisting of wide bandgap NiO and β-phase Ga2O3. We show that the NiO(111) layer can be grown on β-Ga2O3(201) thin films, with an epitaxial relationship of NiO(111)||β-Ga2O3(201) and NiO{110}||β-Ga2O3(132). The p–n diode exhibits a large current rectification ratio of about 6 orders of magnitude at ±2.0 V. A detailed X-ray photoemission spectroscopy study reveals a “staggered” band alignment with valence band offsets of 2.1 eV. More interestingly, a large upward built-in potential of 1.1 eV for β-Ga2O3 is observed near the interface region. The valence band offset and large built-in potential formed at the heterointerface provide advantageous energetics for the separation and migration of photogenerated excitons, of particular interest for self-powered solar-blind ultraviolet photodetection.