Electronic structure and interfacial properties of ZnSe/Si, ZnSe/Ge, and ZnSe/SiGe superlattices

The detailed calculations of electronic structures of the (ZnSe)n/(Si2)m, (ZnSe)n/(Ge2)m, and (ZnSe)n/(Si1−xGe1+x)[x(−1,+1)](110) superlattices are performed by a semi-empirical sp3s∗ tight-binding method with a wide range of n,m⩽20. A strong quantum confinement effect is found that causes the states at the conduction and valence band edges to be confined in two dimensions in the IV semiconductor wells. It is found that the fundamental energy gap increases (up to 2.37 eV for ZnSe/Si and 1.73 eV for ZnSe/Ge at the X˜ point for n=m=2) with decreasing superlattice period, and that the silicon or/and germanium layer plays an important role in determining the fundamental energy gap of the superlattice system due to the spatial quantum confinement effect. The interfacial band structure and planar average of charge densities of states are presented for the ZnSe-Si and ZnSe-Ge boundaries. Two interface bands are identified in the upper region of the thermal gap in these systems, which extend over a quite different region of k-space. Furthermore, the calculated electronic structure of ZnSe/SiGe(110) with a wide range of composition variations is found to be quite different from those of II-VI compounds grown on pure group IV semiconductors, but fairly close to their average.