P-type InGaN alloys

We have demonstrated via electrolyte-based capacitance-voltage (CV) measurements that a set of Mg-doped In$_{1-x}$Ga$_{x}$N thin films (x=.05,.30,.33,and .80) exhibit bulk p-type activity. There is a change in the slope of the Mott-Shockley plots of In$_{1-x}$Ga$_{x}$N with x $\le $ .33 which is consistent with p-type bulk material underneath an n-type surface inversion layer. In contrast, CV analysis of Mg-doped In$_{0.2}$Ga$_{0.8}$N indicates p-type activity throughout the film. These results are consistent with surface Fermi level pinning at --4.9 eV with respect to the vacuum level. Based on the known valence band offsets between GaN and InN, a surface inversion layer is predicted for In$_{1-x}$Ga$_{x}$N with x $\le $ .66 and a surface Schottky barrier for x $>$ .66. These results provide the first evidence of p-type doping of InGaN alloys in the whole composition range.