Ga-doping of nonpolar m-plane ZnMgO with high Mg contents

The electrical and optical properties of m-plane Ga-doped ZnMgO alloys are analyzed by capacitance-voltage profiling, Hall effect, and IR reflectance and UV-VIS absorption spectroscopies, spanning more than four orders of magnitude in electron concentration. Mg contents up to 50% are achieved while maintaining the wurtzite phase, with a measured band-edge energy of 4.41 eV. Despite the deterioration of the electrical properties with Mg incorporation, high electron concentrations (∼4.4×1019cm−3) are measured for Mg contents up to 35%, revealing doping efficiencies close to 100%. The potential physical origin for the drop of the electron concentration and mobility with Mg is analyzed and correlated to the absorption measurements. In ZnO:Ga epilayers band filling is observed, although upon alloying with Mg, bandgap shrinkage and Urbach tailing become evident. It is deduced that the observed carrier compensation arises from the presence of acceptor traps, such as VZn and VZn-GaZn complexes, whereas impurity scattering and electron trapping at extended defects are the mechanisms affecting the mobility.