Influence of Mg composition on the characteristics of MgZnO/ZnO heterostructures grown by co-sputtering

MgZnO/ZnO heterostructures with different Mg compositions were grown on c-sapphire substrates by radio frequency magnetron co-sputtering using two targets, and their microstructural and optical properties were investigated. The analysis showed a blue shift in the ultraviolet emission and a decrease in lattice spacing with increasing power to the MgO target (i.e. increasing Mg composition in the film) up to 200 W at a ZnO target power of 300 W. Further increases in the MgO target power showed an opposite trend, which was attributed to the phase separation into Mg-rich and Zn-rich phases. The film phase separated naturally along the vertical direction and consisted of bottom and top regions, which corresponded to hexagonal and cubic structures, respectively.