2N/2P-Ga/Al/B co-doping scheme for possible n-type diamond: Direct bandgap optimization form first-principles study based on GGA-PBE functional

The structural stability, electronic and optical properties of diamond co-doped with 2N/2P-Ga/Al/B complexes were studied using first-principles calculations based on GGA-PBE functional. Among the five doped systems studied, the NCGaCN configuration (N-C-Ga-C-N) demonstrated the lowest formation energy (E_f = −1829 eV), highest stability, and smallest ionization energy (E_I = 0.101 eV). Band structure and density of states analysis revealed reduced bandgaps in all doped structures, with the most significant reduction occurring in the NCGaCN system. All systems exhibited direct bandgap n-type semiconductor characteristics. The doped systems showed significantly enhanced optical properties, particularly in the PCAlCP and PCGaCP doped systems, where the dielectric constants in the low-energy region increased from 4.2 in intrinsic diamond to 21.8 and 22.5, respectively. Additionally, the conductivity of the NCBCN-doped system reached 21 S/m, and the light absorption coefficient of the NCGaCN-doped system achieved 5.5 × 10⁵ cm⁻¹. These findings provide a solid theoretical foundation for the development of diamond semiconductor materials.