Zn-triggered critical behavior of the formation of highly coherent domains in a Mg_1-xZn_xO thin film on Al₂O₃

A series of Mg_1-xZn_xO (x=0, 0.05, 0.10, and 0.15) thin films were grown by metal-organic chemical vapor deposition on a (0001) sapphire substrate, and the structural characteristics of Mg_1-xZn_xO thin films were investigated by synchrotron x-ray diffraction. The increasing amount of Zn was found to gradually enhance the structural coherence of Mg_1-xZn_xO films. For a sample with 15 at. % of Zn, in particular, the formation of highly coherent domains in Mg_1-xZn_xO was observed to be triggered, with an accompanying phase separation of ZnO. An integrated intensity analysis predicted that the critical concentration x_c of Zn at which the phase separation occurred was 0.086±0.015, and that the highly coherent domains in Mg_1-xZn_xO accounted for 12±1%.