Comparative study of Mg doped ZnO and multilayer ZnO/MgO thin films

MgxZn1−xO (MZO) thin films were deposited from MZO targets as well as sequential deposition of ZnO/MgO multilayers on c-plane Al2O3 substrates using pulsed laser deposition. The total thickness of the films used in this study was ∼300 nm. For multilayer deposition, the thickness of each single ZnO layer was varied in the range of 0.75–2.5 nm followed with the MgO layer thickness of 1 nm. The structural transition from the hexagonal to the cubic phase was observed with the increase in Mg concentration at/above 40% from the single targets. Similar structural change was also observed with the decrease in thickness of single ZnO layer from 2.5 to 0.75 nm in multilayer deposition. The bandgap was increased with increase of Mg contents from 3.3 to 6.2 eV as well as with the change of ZnO sublayer thickness. In both cases it has not been possible to fabricate single-phase stable MZO alloys with a bandgap between 4 and 6 eV.