Axial-strain effects on superlattice band structures

Abstract

The author has used Harrison's (1980, 1983) universal tight-binding method to calculate the valence band (001) axial deformation potential b in group IV and III-V semiconductors. It is found that b= alpha cp(27.4)/d2- alpha csp(16.95)/d2 where d is the bond length in angstroms and alpha cp and alpha csp are the covalency of p and sp3 bonds respectively. This is in reasonable agreement with experiment. A 1% net axial strain then splits the valence band maximum by about 25 meV in most group IV and III-V semiconductors. The resultant bands are anisotropic, with different effective masses parallel and perpendicular to the strain axis. In a strained-layer superlattice, such as GaAs-InAs, significant strain (to about 5%) can be incorporated in each layer, and the highest hole band can then be a light-hole band. The author discusses how it should be possible to achieve hole-based 'effective-mass superlattices' where the light- and heavy-hole confinement well maxima are in different layers of a strained-layer superlattice.