Study of structural transition from metastable zinc-blende to rock-salt crystal in MBE MgS/ZnSe/GaAs multilayer system

The stable bulk crystal structure of magnesium sulphide is rock-salt (RS) However, the metastable zinc-blende (ZB) structure is obtained when MgS is deposited by molecular beam epitaxy (MBE) on (001) zinc-blende substrates with a relatively small misfit. As ZB-MgS is a metastable phase, the ZB crystal structure is easily lost. In the present work the ZB to RS phase transition has been analysed in MgS/ZnSe/GaAs multilayer samples grown by MBE with different MgS layer thickness. By using x-ray diffraction and transmission electron microscopy methods, a partial nucleation of MgS rock-salt is evidenced and correlated to the presence of crystallographic defects (stacking faults) at the bottom interface. The unexpected coexistence of both rocksalt and zinc-blende MgS structural phases is discussed.