Growth and characterisation of MgS/CdSe self-assembled quantum dots

MgS has a very large bandgap of /spl sim/ 5eV and can form an excellent barrier material for wide-gap II-VI quantum structures. Although its stable crystal structure is rocksalt, our group has recently established a novel molecular beam epitaxy (MBE) technique that allows us to grow zinc-blende MgS lattice matched to GaAs substrates to thicknesses greater than 130 nm [1]. The lattice parameter of zinc-blende MgS is almost the same as that of ZnSe. Accordingly, strain between MgS and CdSe is almost identical to that between ZnSe and CdSe and a transition from 2D to 3D growth is expected with increasing CdSe coverage. Using the barrier material MgS with CdSe dots instead of ZnSe has two advantages. Firstly, large band discontinuities, which are estimated to be 2.1 and 0.9eV for the conduction and valence bands, respectively, will provide strong carrier confinement. Secondly, interdiffusion of MgS and CdSe is inhibited due to the immiscibility of these two materials. The clear material boundary between the dots and the barrier will enhance the confinement even further.