Synthesis pathways of BN ₂ co-doped diamond for n-type doping: a theoretical study

Reliable n-type doping, defined here as dopant incorporation that provides a shallow donor ionization energy, sufficient electron activation at room temperature (approximately 300 K), structural stability, and compatibility with chemical vapor deposition/microwave plasma chemical vapor deposition (CVD/MPCVD) growth, remains a central obstacle to the implementation of diamond electronics. In this work, density functional theory calculations are used to examine the formation, stability, and electronic properties of BN2 defect complexes in diamond, with emphasis on feasible defect reaction pathways rather than experimental synthesis. Substitutional B–N complexes were evaluated in 64-, 216-, and 512-atom supercells, and the effect of residual strain was examined over the range from −0.10% to +0.10%. The BN2 complex exhibits a donor ionization energy of 0.132 eV based on charge-state total-energy analysis, consistent with its potential to support electron activation at approximately 300 K. Precursor-referenced reaction-energy analysis indicates that nitrogen-related precursor defects lower the energetic cost of BNx formation, while dissociation reaction-energy calculations show that BN and BN2 are thermodynamically more resistant to the considered neutral decomposition channels than nitrogen-rich BN3 and BN4 complexes. Strain modulates local B–N and B–C bonding and changes the dissociation energetics of BN2. The most favorable neutral route to BN2 formation is the reaction between BN and substitutional N defects, with a reaction energy of −1.04 eV in the 216-atom model. These results identify thermodynamically plausible routes for incorporating BN2 into diamond and provide guidance for precursor-, strain-, and temperature-controlled CVD/MPCVD growth of n-type diamond.