Identification and characterization of defect levels in GaN by radioactive isotopes

In this work the optical and electrical properties of the dopands Se, Ag, Hg, Au, Cd, Pt, Br, As, Ge and the formation of anti-site defects in GaN were investigated by photoluminescence spectroscopy and Hall effect measurements by using radioactive isotopes. The change of spectral or electrical features at a rate consistent with the half-life provides confirmation of the chemical identity of the impurity involved in the corresponding defect. The changes of the PL intensities as a function of time after implantation and annealing could be perfectly described by using exponential fits with the corresponding half-lives of the isotopes and therefore an unequivocal chemical assignment of all observed transitions was done for the first time.Additionally Hall effect measurements were performed to investigate the influence of these dopands on the carrier concentration, specific resistivity and mobility of the carriers.A suitable annealing procedure is necessary to achieve an efficient electrical and optical activation of the implanted dopands. The performance of different annealing methods was characterized with PAC measurements. After annealing GaN at 1373 K in an ammonia atmosphere only 60 of the probe atoms are located on unperturbed lattice sites. Annealing temperatures up to 1585 K are possible if one adds Al during the annealing procedure. This procedure led to an improved incorporation of 85 of all probe atoms on unperturbed substitutional lattice sites.Hall-effect measurements show that annealing at 1523 K activates 22 of the implanted dopands substituting a Ga-site, while only 6 of the implanted dopands substituting a N-site are electrically activated