Electrical characterization of Mg-doped GaN grown by metalorganic vapor phase epitaxy

We have applied frequency-dependent capacitance measurements and admittance spectroscopy on GaN:Mg to study the electronic states associated with Mg doping. Metalorganic vapor phase epitaxy GaN:Mg samples with two different Mg doping levels were grown and thermally annealed in nitrogen. Lateral dot-and-ring Schottky diodes using Au/Ti were fabricated. Frequency-dependent measurements on these diodes show that the capacitance is reduced at a higher frequency, most likely due to the inability of a deep center to maintain an equilibrium ionization state under a high-frequency modulation. Admittance spectroscopy, in which the conductance is monitored as a function of temperature, verifies the existence of one impurity-related acceptor level in the higher Mg-doped sample with an activation energy of 136 meV. For the lower Mg-doped sample, two acceptor levels at 124 and 160 meV were observed. We believe these levels are most probably associated with the Mg acceptor state itself, possessing energy levels which are very close to the results previously reported in the literature. (C) 1996 American Institute of Physics.