Efficient p-type doping of GaN films by plasma-assisted molecular beam epitaxy

In this paper we report on the mechanism of efficient incorporation of Mg in GaN films during growth by plasma-assisted molecular beam epitaxy. It is found that Mg incorporates more efficiently during growth of GaN films at high temperatures (770 degreesC) under extreme Ga-rich conditions. We propose that this result is due to the dissolution of Mg in the excess Ga on the growth surface and its incorporation into the GaN film via liquid-phase processes. Transport measurements at 300 K together with secondary-ion-mass-spectroscopy indicate that the Mg-doping efficiency of GaN under these conditions of growth is 10%. Using this method of doping, p-type GaN films free of Ga droplets, with hole concentrations varying from 2x10(17) to 3x10(18) cm(-3) and corresponding mobilities varying from 30 to 2 cm(2)/V s, are obtained. The lowest resistivity achieved is 0.3 Omega cm. (C) 2004 American Institute of Physics.