Effect on chlorine incorporation as Mg is alloyed into ZnSe

We have investigated chlorine incorporation in ZnSe and ZnxMg1-xSe through both modeling and experiment. Solubility issues, native defects and chlorine-impurity-related defects have been studied using the ab initio full potential linear muffin-tin-orbital method. Our calculations indicate that the addition of Mg reduces the formation energy for chlorine on the Se site, thereby predicting increased solubility. Subsequent chlorine doping experiments in ZnxMg1-xSe using molecular beam epitaxy indicated significantly higher chlorine incorporation in the presence of magnesium, directly supporting the prediction of the calculations. Calculations support the strong tendency for the formation of a defect complex between a chlorine impurity at the Se site and a vacancy at the neighboring Zn site for heavy n-type doping. The formation of this defect serves to compensate, i.e., negate, the chlorine as an n-type dopant. Experimental observations indicated that significant compensation occurs for heavy Cl doping. There are competing mechanisms that contribute to the effect of magnesium on chlorine when used as an n-type dopant in ZnSe. First, the formation energies for chlorine substituting for selenium decrease in the presence of magnesium. Second, the formation energies of the Cl-Se-V-Zn complex also decrease. Finally, the band gap increases in the presence of magnesium, decreasing the net electron concentration at room temperature. Thus, the net effect of adding magnesium is to decrease the maximum achievable carrier concentration through the use of chlorine as an n-type dopant.