Structural and optical properties of single-phase ZnO1−xSx alloy films epitaxially grown by pulsed laser deposition

We report on a detailed investigation of the structural and optical properties of single crystalline ZnO1−xSx thin films, placing emphasis on the elucidation of the correlation of the band gap and lattice parameters, particularly the lattice constant a, with the S content in the alloy films. High-quality ZnO1−xSx thin films with different S concentrations Xs (0 ⩽ Xs ⩽ 0.18) were grown epitaxially on c-plane sapphire substrates by pulsed laser deposition using a ZnS ceramic target with varying O2 partial pressures. X-ray diffraction studies revealed that all grown ZnO1−xSx thin films have a single-phase wurtzite structure. With increasing Xs value from 0 to 0.18, both lattice constants c and a expand monotonically from 5.204 to 5.366 Å and from 3.255 to 3.329 Å, respectively, while the optical band gap shrinks from 3.27 to 2.92 eV with a bowing parameter of 2.91 eV. Based on these information, ZnOS/MgZnO heterostructures that have a perfect in-plane lattice match and a maximum barrier height can be proposed, which might eventually lead to new optoelectronic devices with superior performance.