Effects of Doping on Valence Band Offset in Al₂O₃-Deposited on H-Terminated Doped Diamond

An investigation has been conducted on H-terminated, highly boron-doped polycrystalline diamond (HBPD) (10x10 mm, 600 nm thick,10²⁰ atoms/cm³), moderately boron-doped single-crystalline diamond (MBSD) (5x5 mm, 500 nm thick, 10¹⁸ atoms/cm³), and moderately phosphorus-doped single-crystalline diamond (MPSD) (3x3 mm, 200 nm thick, 10¹⁸ atoms/cm³). A thin layer of Al₂O₃ was grown on the H-terminated diamond surfaces using plasma-enhanced atomic layer deposition (PEALD), and changes in the hole accumulation layer were monitored via the binding energy of the diamond.
The electronic band configurations were characterized using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The valence band offsets (VBO) and conduction band offsets (CBO) for HBPD were found to be 0.4 eV and 0.83 eV, respectively, while for MBSD, they were 1.9 eV and -0.67 eV. For MPSD, the VBO and CBO were 0.6 eV and 0.63 eV, respectively. It was observed that the VBO for moderately boron-doped single-crystalline diamond (MBSD) is significantly higher than that for highly boron-doped polycrystalline diamond (HBPD). The VBO and CBO for lightly boron-doped single-crystalline diamond (10¹⁷ atoms/cm³), as reported by Yang et al. (J. Appl. Phys. 122, 155304 (2017)), were 2.7 eV and -1.5 eV, respectively. H-plasma treatments were performed on the MBSD and MPSD samples after each Al₂O₃ deposition. Post-treatment, the valence band maximum (VBM) was found to be higher than that of the Al₂O₃-deposited diamond, indicating that the plasma treatment reduces Al₂O₃ defects and enhances its passivation effect.
This study is useful in understanding Al₂O₃/H-diamond heterojunctions for the fabrication of MOSFETs. While lower VBO may promote tunneling, which is helpful in applications like high electron mobility transistors (HEMTs), higher VBO can lead to improved carrier confinement in quantum wells, improving the optical properties in optoelectronic devices and the thermal stability of heterojunctions.

This research was support by the NSF through grant DMR-2003567 and the U.S. Department of Energy, Office of Science, Basic Energy Sciences through ULTRA, an Energy Frontier Research Center under Award #DE-SC0021230