Cubic ZnxMg1-xO and NixMg1-xO thin films grown by molecular beam epitaxy for deep-UV optoelectronic applications

Oxide based compounds have been of increasing interest for wide bandgap, deep ultraviolet optoelectronics. While high Al content AlGaN has enabled many UV-DUV technologies, it suffers inherent drawbacks including difficulty achieving increasing Al incorporation, high threading dislocation densities and challenges in bandgap engineering due to polarization and piezoelectric effects. Here we present two wide bandgap cubic oxide compounds, ZnMgO and NiMgO, that offer advantages over AlGaN for deep ultraviolet (DUV) applications. Ni(x)Mg(1-x)O and Zn(x)Mg(1-x)O are both direct band gap, cubic rocksalt (B1) semiconductors with bandgaps in the UV-DUV spectral regions, offering alternatives without the aforementioned drawbacks associated with AlGaN. Here we present Ni(x)Mg(1-x)O and Zn(x)Mg(1-x)O thin films grown by plasma-assisted MBE on lattice matched MgO substrates as a novel means by which to realize DUV detection devices. In both systems we have shown the films to exhibit abrupt, continuously tunable absorptions edges over their respective bandgap ranges. Ni(x)Mg(1-x)O films were varied compositionally from x=0 to 1, realizing bandgaps from 3.5 to 7.8 eV. Zn(x)Mg(1-x)O films were similarly varied over the entire B1 range of the ternary (0<x<0.42) and show bandgap tunability from similar to 5 to 7.8 eV. All films are characterized through Rutherford backscattering (RBS), x-ray diffraction (XRD), atomic force microscopy (AFM) measurements and optical transmission. Significantly, we have successfully fabricated solar blind detectors in both categories and highlight the results from Ni(x)Mg(1-x)O here.