Temperature dependent self-compensation in Al- and Ga-doped Mg0.05Zn0.95O thin films grown by pulsed laser deposition

We studied the doping efficiency of Al and Ga dopants in (Mg, Zn) O alloys as a function of the growth temperature and post growth annealing times. High-temperature growth results in the highest structural quality and highest electron mobility; the doping efficiency is limited by the dopant's solubility. It was investigated in detail that a low growth temperature is needed to achieve free carrier densities above the solubility limit of the dopants. Samples grown at temperatures of 300 degrees C and below have a free carrier density significantly above the solubility limit yielding the minimum resistivity of rho(min) = 4.8 x 10(-4) Omega cm for Mg0.05Zn0.95O:Al thin films grown on glass at 300 degrees C. Annealing of these samples reduces the free carrier density and the absorption edge to values similar to those of samples grown at high temperatures. The saturation of the free carrier density and the optical bandgap at their high temperature growth/annealing values is explained by the thermal creation of acceptor-like compensating defects in thermodynamic equilibrium. Published by AIP Publishing.