Electrical characterization of Mg-related energy levels and the compensation mechanism in GaN:Mg

We investigated GaN:Mg samples grown by metal-organic chemical vapor deposition using various electrical measurement techniques. Annealing of highly resistive as-grown samples for different duration of time gives gradual activation of accepters to concentrations up to 1x10(17)cm(-3) Conductance measurements of the annealed samples show the presence of two hole traps H1 and H2 with activation energies 130 and 170 meV from the valence band, respectively. The concentration of the H2 trap is always found to be Pow in our samples. The H1 trap is the shallowest one in our samples. Its concentration is directly proportional to the electrically active acceptor concentration in the samples, increasing with annealing. Hence, we attribute it to a Mg-related acceptor. This assignment is confirmed by dark current measurements. Two electron traps at 280 and 580 meV from the conduction band are observed in optical deep-level transient measurements. They have, too weak concentrations to influence the fi-ee carrier concentration. We conclude that the hole conductivity observed in the annealed GaN samples is produced through thermal dissociation of passivating H donors from Mg accepters. Most of the Mg concentration in the samples remains electrically inactive, however. (C) 2000 American Institute of Physics. [S0021-8979(00)03321-1].