Band structures, optical transition strengths and their pressure dependence of (GaP) n(AlP) n short-period superlattices with n=3 to 10

Abstract

The electronic structure and optical transition strengths of (GaP) n(AlP) n short-period superlattices with the clean (001) interface (SL(n,n)) are calculated for n=3 to 10 using the first principle pseudopotential method within the local density approximation (LDA). The calculated results show that SL(n,n) are pseudo-direct gap semiconductors for n=3 to 10. The calculated optical transition strengths for the pseudo-direct gap transitions oscillate between even and odd n-values and those for even n-values are as strong as those of direct-gap-semiconductors, though the transition strengths decrease gradually with increasing n. In order to investigate the character of the pseudo-direct gap, the hydrostatic pressure dependence of the pseudo-direct band-gap energy and of the optical transition strength for SL(4,4) is also calculated. The result predicts that the band-gap becomes smaller, i.e. the absorption edge exhibits a red shift, and the optical transition strength decrease gradually by applying pressure and thus that the conduction band state at the fundamental absorption edge is the X z state folded into Г.