Controllable band-gap engineering of the ternary Mg_xNi _{1 - X}O thin films deposited by radio frequency magnetron sputtering for deep ultra-violet optical devices

The ternary Mg_xNi_{1 - x}O thin films were deposited on glass substrates by radio frequency (RF) magnetron co-sputtering with NiO and MgO targets. The Mg mole fraction was controlled by RF power of MgO target from 0 to 200 W at 600 C. As a result, the absorption edge was proportionally shifted from 330 nm (3.75 eV) to 314 nm (3.95 eV), when RF power of MgO target increased. The Mg composition was easily mixed up to 4.9% in the Mg _xNi_{1 - x}O thin films when the RF power for MgO was 200 W, which was confirmed by secondary ion mass spectrometry data showing similar changes in the Mg mole fraction. In addition, the transmittance of all films maintained at an average value of 80% in the visible region and no significant structural changes were observed, regardless of the Mg contents, because of the identical rock-salt structure and low lattice mismatch (0.8%) between NiO and MgO.