Features of free carrier and exciton recombination, diffusion, and photoluminescence in undoped and phosphorus-doped diamond layers

We investigated carrier dynamics and photoluminescence in undoped and n-type phosphorus-doped diamond epilayers under interband picosecond-pulse photoexcitation at 213nm. Carrier/exciton lifetime and diffusion coefficient D were determined in 4×1017 to 4×1019cm−3 carrier density range. The low D=7÷11cm2/s value in the undoped epilayer was ascribed to exciton formation and contribution of many-body effects. At low excitations, photoluminescence spectra in the undoped layer exhibited exciton emission, while at the higher ones (above 2×1018cm−3) free carrier emission became dominant. The calculated radiative lifetime of excitons (860ns) was found much higher than the experimentally measured nonradiative lifetime of 11ns, governed by excess carrier diffusive flow to the surface, with S=(3±2)×105cm/s surface recombination velocity. In the n-type layer, donor-related emission dominated and the phosphorus-related defect complexes diminished the carrier lifetime to 30–50ps. Optically recharged phosphorus states resulted in millisecond long decay tails of trapped carriers.