Layers grown by metal organic vapor phase epitaxy onto sapphire were implanted with 90keV Mg ions to achieve p-type conductivity. However, besides the Mg acceptors the implantation process also induces additional defects with compensating impact preventing the p-type conductivity wanted. The approach to reducing this compensation effect was based upon defect passivation by S; achieved by the co-implantation of 150keV S ions in various implantation sequences. The corresponding implantation induced defect states were characterized by various electrical and photoelectrical spectroscopy techniques, e.g. deep level transient spectroscopy and admittance spectroscopy. Regardless of the implanted ion species and of the implantation sequence, 4 implantation-induced electron traps were found, with thermal activation energies of between 0.14 and 1.1eV. These were typical of all single and co-implanted layers. The depth-resolved concentration profile of these intrinsic defects determined by deep level transient spectroscopy at different bias voltages corresponded either to the profile of the introduced ions or to those of the generated vacancies as predicted by simulations. Besides this normal implantation induced defect generation, signs of passivation effects due to S were found in the optical admittance spectra where contributions from deep states as well as from the Mg acceptor could be drastically suppressed. Remarkably, these effects significantly depended upon the implantation sequence, e.g. whether Mg or S ions were implanted last.

Electrical Characterization of Deep Defect States in Gallium Nitride Co-Implanted with Magnesium and Sulfur Ions. A.Krtschil, A.Kielburg, H.Witte, A.Krost, J.Christen, A.Wenzel, B.Rauschenbach: Materials Science and Engineering B, 2002, 93[1-3], 85-9