Nitrogen centers in GaP produced by hot implantation

Backscattering yields of 1.5 MeV-He+ ions and low temperature photoluminescence (PL) spectra were measured in GaP crystals implanted with 200 keV-N+ ions as functions of ion-dose, temperature during implantation and annealing temperature after implantation. Backscattering results indicate that hot implantation at 5000C greatly reduces radiation damage. The PL intensities of NN lines become maximum in the sample implanted with N+ ions of 3 x 1014 cm-2 at 5000C, and annealed at 10000C for 1 hr with aluminium glass. The PL intensity is comparable to that of the nitrogen-doped sample during liquid phase epitaxy which is widely accepted as the best method of introducing nitrogen into GaP crystals. In the case of 5000C - hot implantation, the radiation damage produced during implantation is annealed out at 700 to approximately 8000C and the implanted nitrogen substitutes for the phosphorous sites after annealing at 900 to approximately 10000C. Some kinds of defects or strains remain around the NN centers even in implanted samples with a maximum PL efficiency. These defects or strains do not seem to reduce the PL efficiency. In the case of room temperature implantation, PL efficiency decreases to one-hundredth or one-thousandth due to the formation of the non-crystalline state compared with hot implantation. (author)