Band Offset of PECVD h-BN Film on Doped-Diamond

The interface between hexagonal boron nitride (h-BN) and diamond presents intriguing possibilities for next-generation electronic devices. This study explores the band offset at the interface of thin h-BN films grown in polycrystalline boron-doped (B-doped) diamond and single crystalline (111) phosphorous-doped (P-doped) diamond. In this study, BN was deposited via ECR-PECVD using fluorine chemistry, with the h-BN phase achieved by controlling the H₂ to BF₃ precursor ratio. The interfaces were explored using stepwise deposition followed by X-ray and UV photoelectron spectroscopy (XPS) (UPS). The thicknesses of the first and second BN layers were measured to be around 4 nm and 8 nm, respectively. The presence of the π-plasmon in the B 1s and N 1s spectra of the thin BN layer indicated that the surface consisted primarily of h-BN. The measured valence band offsets (VBO) were found to be -1.6 eV for the B-doped diamond and -1.2 eV for the P-doped diamond, indicating a significant influence of substrate doping on the band alignment. Boron, being a p-type dopant, introduces acceptor levels at ~0.3 Ev from the valence band maximum, while phosphorus, an n-type dopant, creates donor levels at ~0.6 eV from the conduction band minimum. We suggest that these dopant-induced changes in the diamond’s electronic structure directly affect the band alignment with the h-BN overlayer. The combination of growth conditions and substrate doping synergistically influences the final band alignment. For B-doped diamond, the increased band offset may be attributed to the alignment of acceptor states in the diamond with the valence band edge of h-BN. Conversely, P-doping appears to reduce the band offset, possibly due to Fermi-level pinning effects at the interface. The interplay between film growth conditions, doping type, and crystallinity directly impacts the band alignment, which is crucial for optimizing charge transport across the interface.
These findings provide insights into the tunability of the electronic properties of h-BN/diamond heterostructures and suggest that careful control over doping and deposition processes can enable tailored band offsets for specific applications. The observed difference in VBO between B-doped and P-doped substrates offers opportunities for band engineering by selectively doping the diamond substrate. Our future work will focus on a more comprehensive investigation of how various PECVD parameters and surface termination affect the band alignment.

This research was supported by the NSF through grant DMR-2003567 and the DOE through the ULTRA EFRC, DE-SC0021230.