Metastable zinc-blende MgS structure: Combined experimental and theoretical study

Abstract

MgS/ZnSe/GaAs multilayers with the MgS thickness ranging from 20 to 140 nm were grown at $300\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ by molecular-beam epitaxy on [001] GaAs substrates. The samples were studied by using several x-ray methods and transmission electron microscopy. The coexistence of metastable zinc-blende (ZB) and rocksalt MgS structural phases was evidenced and discussed. The analysis of reciprocal space maps of the x-ray intensity distribution around asymmetrical reciprocal-lattice nodes allowed us to determine the strain status of the MgS layers and to show that the ZB-MgS phase was pseudomorphic also in the case of the thickest film. The lattice parameter of the pure Ζ\ensuremath{\mathrm{B}}-MgS phase ranging between $0.563\text{ }33<{a}_{\text{MgS}}<0.563\text{ }67\text{ }\text{nm}$ was obtained by extrapolation from x-ray diffraction data and predicted ab initio elastic constants, taking into account that there was a Zn incorporation during the MgS growth estimated in the range $0.005\ensuremath{\le}{x}_{\text{Zn}}\ensuremath{\le}0.02$.