Band Alignment and Interface Electronic Structure of Al₂O₃ Deposited on H-Terminated Boron and Phosphorous Doped Diamond

This study investigates H-terminated, highly boron-doped polycrystalline diamond (HBPD), moderately boron-doped single-crystalline diamond (MBSD), and moderately phosphorus-doped single-crystalline diamond (MPSD). A conformal Al₂O₃ dielectric layer was deposited on H-terminated diamond (H-diamond) surfaces via plasma-enhanced atomic layer deposition (PEALD). Post H-plasma treatments restored surface conductivity by passivating interfacial defects and re-establishing H-termination. Band alignment and valence band offsets (VBOs) at the Al₂O₃/H-diamond interface were determined using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). HBPD and MBSD showed a consistent VBO of 2.7 eV, while MPSD exhibited a significantly reduced VBO of 0.9 eV. The results provide new insights into the band alignment and interface control of Al₂O₃/H-diamond heterostructures, which are crucial for optimizing metal-oxide-semiconductor field-effect-transistors (MOSFETs) and related devices. The higher VBO for boron-doped diamond enhances carrier confinement and device performance, whereas the lower VBO for phosphorus-doped diamond could passivate PIN structures.