Band alignment of indium tin oxide (ITO) and aluminum-doped zinc oxide (AZO) on non-hydrogenated and H-terminated (100) diamond

Abstract

We report the band alignments of ITO/diamond and AZO/diamond heterostructures, comparing hydrogen-terminated (H-diamond) and non-hydrogenated (O-diamond) surfaces using x-ray photoelectron spectroscopy (XPS). For O-terminated diamond, both ITO and AZO exhibit a type II (staggered gap) alignment, with valence band offsets (VBOs) of −0.13 ± 0.03 eV and −0.86 ± 0.18 eV, respectively. In contrast, H-termination induces a transition to the type I (nested) alignment, with significantly reduced VBOs (<0.2 eV). Surprisingly, despite the negative electron affinity (NEA) of H-diamond, its conduction band minimum (CBM) lies below that of ITO/AZO—a reversal from the O-terminated case. This shift is attributed to the strong upward movement of the valence band maximum (VBM) in H-diamond (3.32 ± 0.60 eV vs 1.29 ± 0.20 eV for O-diamond), which lowers the CBM relative to the oxide layers. Additionally, H-termination minimizes interfacial disorder and Fermi-level pinning, facilitating a band alignment favorable for Ohmic contact formation. These findings demonstrate that while NEA influences vacuum-level positioning, interfacial band bending and VBM shifts dominate heterojunction energetics. The reduced offsets on the H-terminated surfaces suggest that ITO/AZO interlayers can enhance hole injection in diamond-based devices, offering a pathway to improved Ohmic contacts in high-power electronics.