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

MgS/ZnSe/GaAs multilayers with the MgS thickness ranging from 20 to 140 nm were grown at 300 ° 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 -MgS phase ranging between 0.563 33aMgS 0.563 67 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 0.005xZn 0.02.