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

Abstract

• We grew epitaxial ZnO 1- x S x ( x ≤ 0.18) films by PLD with a ZnS ceramic target and O 2 . • Lattice parameters ( c , a ) and E g of single-phase ZnO 1−x S x alloys were determined. • C and a expand from 5.204 to 5.366 Å and 3.255 to 3.329 Å with increasing S content. • The optical bandgap shrinks from 3.27 to 2.92 eV with a bowing parameter of 2.91 eV. • In-plane perfectly matched ZnOS/MgZnO heterostructures with max. barrier are proposed. We report on a detailed investigation of the structural and optical properties of single crystalline ZnO 1 − x S x 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 ZnO 1 − x S x thin films with different S concentrations X s (0 ⩽ X s ⩽ 0.18) were grown epitaxially on c -plane sapphire substrates by pulsed laser deposition using a ZnS ceramic target with varying O 2 partial pressures. X-ray diffraction studies revealed that all grown ZnO 1 − x S x thin films have a single-phase wurtzite structure. With increasing X s 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.