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 rock-salt (RS) MgS structural phases were 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 were pseudomorphic in also the case of the thickest film. The lattice parameter of the pure ZB-MgS phase ranging between 0.56333 aMgS 0.56367 nm was obtained by extrapolation from X-ray diffraction data, taking into account that there was a Zn incorporation during the MgS growth estimated in the range 0.005 d xZn d 0.02, and predicted ab initio elastic constants.