Unlocking n-type semiconductivity in diamond: A breakthrough approach via surface metal doping

Device applications of ultra-wide bandgap diamond rely on controlled carrier types and concentrations, yet conventional n-type doping in diamond has been challenging due to its strong covalent bonds. Surface charge transfer doping (SCTD) provides an effective alternative, utilizing energy level differences between surface dopants and semiconductors to modulate carrier properties. In this study, we examined n-type SCTD doping on oxygen- and fluorine-passivated diamond (100) surfaces [diamond(100):Y, where Y = O, F] using alkali metals (Na, K, Rb, and Cs) through first-principle calculations. Following surface metal doping of diamond(100):Y, electron enrichment shifted the Fermi level into the conduction band, confirming effective n-type doping. The maximum areal electron densities reached 2.50 × 1014 cm−2 for diamond(100):O and 2.00 × 1014 cm−2 for diamond(100):F, exceeding the previously reported optimal values for surface organic molecule doping. For diamonds of equal thickness and identical passivating atoms, charge transfer followed the trend Na > K > Rb > Cs, inversely related to atomic radius. With increasing diamond thickness, charge transfer rose for oxygen-passivated surfaces and declined for fluorine-passivated ones before stabilizing, corresponding to the conduction band minimum (CBM) shift: downward for oxidization and upward for fluorination. For all alkali metal surface doping, charge transfer was greater in diamond(100):O than in diamond(100):F, owing to the lower CBM of oxidized diamond. Overall, effective n-type SCTD doping is critically influenced by diamond’s CBM levels—dependent on its thickness and surface passivation—and the metal atom’s radius. These findings provide theoretical insights into advancing diamond-based electronic and optoelectronic devices.