Al composition dependence of band alignment in NiO/(AlxGa1−x)2O3 heterojunctions

This study investigates the electronic band alignment of the p-NiO/n-(AlxGa1−x)2O3 heterojunction, a promising candidate for next-generation power electronics. High-quality β-(AlxGa1−x)2O3 thin films with varying aluminum content (x = 0.1, 0.2, and 0.3) were grown on sapphire substrates by metalorganic vapor-phase epitaxy, followed by the deposition of p-type NiO via magnetron sputtering. The band offsets were experimentally determined using x-ray photoelectron spectroscopy via the Kraut method. Our findings reveal a type-II, staggered band alignment at the interface. The valence band offset (VBO) was measured to be highly negative, ranging from −1.63 eV for x = 0 to −1.29 eV for x = 0.3. In contrast, the conduction band offset (CBO) was found to be smaller and decreased with increasing aluminum content, even becoming negative at the highest Al content. The large, negative VBO creates a significant barrier for holes, leading to strong hole confinement within the NiO layer. This is particularly beneficial for vertical power rectifiers, as it results in low reverse leakage currents and high breakdown voltages, addressing a major limitation of conventional Schottky rectifiers. Conversely, the small or negative CBO results in weak electron confinement, which poses a challenge for lateral field-effect transistors by potentially increasing gate leakage current. The ability to tune the band alignment by controlling the Al content provides a pathway for rational device design. This research provides crucial experimental data for the development of high-voltage NiO/(AlxGa1−x)2O3 power devices, positioning them as a viable alternative to established SiC and GaN technologies.