Optical and Electrical Properties of CVD Boron-Doped Diamond Following HPHT Annealing

Boron-doped diamond (BDD) is a promising material for semiconductor applications due to diamond's outstanding properties. Nonetheless, achieving efficient p-type conductivity remains challenging as relatively deep acceptor level at low boron doping concentrations yields low activation efficiency, limiting room temperature carrier concentration, while heavy doping reduces mobility through impurity scattering and defect formation. This study aims to address these issues via high-pressure and high-temperature (HPHT) annealing. Chemical vapor deposition (CVD)-grown BDD samples were annealed at 5 GPa across 1100 to 2000 ℃ to systematically investigate electrical and optical properties evolution. The results demonstrate that annealing at suitable temperature increases carrier concentration by more than an order of magnitude and electrical conductivity by over fourfold, with the effect strongly dependent on annealing temperature and doping concentration. Comprehensive spectroscopic analyses reveal several factors contributing to the annealing temperature-dependent behavior of carriers, including lattice strain relaxation, modifications in boron-bound excitons, and nitrogen-vacancy center transformation. Additionally, the optimal annealing temperature varies significantly with doping concentration. These findings indicate that HPHT processing is a viable approach to overcome doping constraints in BDD, advancing its implementation in electronic devices.