D. Seghier et Hp. Gislason, Electrical characterization of Mg-related energy levels and the compensation mechanism in GaN : Mg, J APPL PHYS, 88(11), 2000, pp. 6483-6487
We investigated GaN:Mg samples grown by metal-organic chemical vapor deposi
tion using various electrical measurement techniques. Annealing of highly r
esistive as-grown samples for different duration of time gives gradual acti
vation of accepters to concentrations up to 1x10(17)cm(-3) Conductance meas
urements 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, respect
ively. The concentration of the H2 trap is always found to be Pow in our sa
mples. 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-r
elated acceptor. This assignment is confirmed by dark current measurements.
Two electron traps at 280 and 580 meV from the conduction band are observe
d in optical deep-level transient measurements. They have, too weak concent
rations 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].