Optical and dielectric properties of CuAl2O4 films synthesized by solid-phase epitaxy

The synthesis and properties of CuAl2O4 thin films have been examined. The CuAl2O4 films were deposited via reactive direct current magnetron sputter using a CuAl2 target. As-deposited films were amorphous. Post-deposition annealing at high temperature in oxygen yielded solid-phase epitaxy on MgO. The film orientation was cube-on-cube epitaxy on (001) MgO single-crystal substrates. The films were transparent to visible light. The band gap of crystalline CuAl2O4 was determined to be ∼ 4 eV using a Tauc plot from the optical transmission spectrum. The dielectric constant of the amorphous films was determined to be ∼ 20–23 at 1–100 kHz.