Oxygen-Assisted B-N Codoping Enables Shallow BN₂ Donors for n-Type Diamond

Achieving stable n-type conductivity in diamond has remained a central challenge due to the deep donor levels and compensation associated with conventional dopants. Here, we show that oxygen-assisted B-N codoping during microwave plasma chemical vapor deposition activates shallow BN₂ donors within a narrow thermal window (~1,020 K), yielding reproducible electron conduction. First-principles calculations identify the BN₂ complex-stabilized via oxygen-mediated regulation of N site occupancy that suppresses deeper N-related defects-as a shallow and strain-tolerant donor, consistent with the experimentally optimized growth window for BN₂ codoping. The resulting films exhibit electron concentrations above 10¹⁹ cm^-3 with a mobility of 4.05 cm²/(V·s) and a shallow activation energy of ~21.1 meV, confirming effective n-type transport. Integration with p-type 2H-MoTe₂ yields a diamond-based pn junction with clear rectifying behavior. While device performance is presently limited by interface states, these findings establish BN₂ codoping as a viable strategy for n-type diamond and highlight interface quality as the decisive frontier for diamond electronics, opening opportunities for high-frequency, high-power, and radiation-hard device platforms.