P-type surface charge transfer doping of diamond via low-dimensional transition metal oxides

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Device applications of ultra-wide-bandgap diamond rely on the precise control of both carrier type and concentration. However, due to the strong covalent bonds in bulk diamond, conventional doping methods have struggled to achieve large-scale tuning of its properties. Surface charge transfer doping (SCTD) is seen as a simple and effective solution, leveraging energy-level differences between surface dopant and the semiconductor to regulate carrier properties efficiently. Here, we conducted a comprehensive theoretical study on p-type SCTD of hydrogen-terminated diamond (100) surface [diamond(100):H] using low-dimensional transition metal oxides. The doping effects of the molecular MoO3 and monolayer MoO3 were first explored. The areal hole density for molecular-MoO3-doped diamond(100):H sharply rises and then slightly decreases with increasing MoO3 density, reaching a peak of 7.55 × 1013 cm−2—surpassing the maximum value achieved with a MoO3 monolayer. For identical MoO3 densities, a stronger interaction with diamond(100):H results in a greater areal hole density. We also studied one-dimensional chain-like CrO3 and two-dimensional layered V2O5. However, a V2O5 monolayer cannot achieve the saturation areal hole density due to the large energy separation between the conduction band minimum (CBM) of V2O5 and the valence band maximum (VBM) of diamond(100):H. Increasing the number of V2O5 monolayers will enhance the doping effect. Overall, optimal doping can be achieved with smaller dimensions, higher density and thickness of the transition metal oxides, stronger interactions with diamond(100):H, and a larger energy separation between the dopant's CBM and diamond(100):H's VBM. This study provides theoretical guidance to develop superior diamond-based electronic and optoelectronic devices.