Layers grown by molecular beam epitaxy onto c-axis oriented sapphire substrates were implanted with 180keV Mg ions to doses of between 1014 and 1016/cm2. The implantation-induced defect states were investigated by means of temperature-dependent conductivity and thermal or optical admittance spectroscopy. Dominant carrier emissions, with thermal activation energies of between 0.36 and 0.80eV, were found. These states were attributed to implantation-induced electron traps, since they did not appear in the non-implanted reference sample. Defect states with similar transition energies were also observed in optical admittance spectroscopy; resulting in an enhancement of defect-to-band transitions in the near-bandgap region around 3.45eV, in the blue band around 3.0eV, as well as in the mid-gap range for photon energies of between 2.5 and 1.80eV, respectively. In addition, new transitions were found at 2.1 and 1.95eV. Furthermore, transitions from implantation-induced shallow states (the Mg acceptor and a new donor level at about 0.07eV) were observed and tentatively attributed to a N vacancy. The critical ion dose for amorphization was deduced to be between 5 x 1015 and 1016Mg+/cm2 by using X-ray diffraction.

Electrical Characterization of Magnesium Implanted Gallium Nitride. A.Krtschil, A.Kielburg, H.Witte, J.Christen, A.Krost, A.Wenzel, B.Rauschenbach: Journal of Applied Physics, 2002, 91[1], 178-82