Donor phosphorus interactions observed by bound exciton luminescence in CVD diamond

Two phosphorus-doped CVD diamond layers with nominal concentrations of 3 × 1018 cm− 3 and 1 × 1019 cm− 3 were studied by low-temperature cathodoluminescence. The measurements show that the effective doping concentration varies systematically across the sample area. Exciting individual spots with increasing local donor densities we observe novel bound exciton lines to appear and finally to dominate the spectra. The new lines are down-shifted from the conventional P-bound exciton line by up to ≈ 80 meV. They were studied as a function of excitation level and temperature. The data lead us to conclude that excitons can bind to phosphorus pairs with different spacings giving evidence for exciton–donor pair interactions.