Tight-binding calculations: Electronic structure and interfacial properties of (ZnSe)n / (Si 2) msuperlattices

Abstract

We have calculated the electronic properties of the (ZnSe) n/(Si2 ) m(110) superlattices (SLs) with n= 2–16 paying particular attention to the role of the interface states at the Zn–Si and Se–Si interfaces. The calculations are performed by means of a semiempirical tight-binding method with an sp 3s *basis. The presence of the electric field in the SL is totally ignored, i.e. ‘the zero-field model`. For the (ZnSe) 16/(Si2 ) 16(110) SL, the bandgap is 1.34 eV, with the conduction-band minimum at the X point. The states at the conduction and valence-band edges are confined two dimensionally in the Si layers. It is found that the fundamental energy gap increases (up to 2.10 eV at the X point for n=m= 2) with decreasing SL period and the Si layer plays an important role in determining the fundamental energy gap of the SL system due to spatial quantum confinement effects. For all reasonable values (ranging from 0 to 3.0 eV) of the valence-band discontinuity used in the calculation, there is an empty interface band in the upper region of the gap of the (ZnSe)n/(Si 2) m(110) (n, m⩽ 20) system and the conduction band minima shift from X to Γ along _____ ΓX while increasing the band offset.