Interband transitions in [001]-(GaP)1(InP)m superlattices

We study the optical interband transitions of [001]-(GaP)1(InP)m monolayer superlattices on (001) InP for m=5, 14, 27 and 51 using spectroscopic ellipsometry for photon energies from 1 to 6 eV. Samples were grown by metal-organic vapor phase epitaxy. We determine the InP-like E0, E0+Δ0, E1, E1+Δ1, and E2 transitions from lineshape analysis of the pseudodielectric function 〈ε〉. The E0 and E0+Δ0 interband transitions depend on m due to effective alloying, strain, and symmetry reduction upon the superlattice period. Empirical pseudopotential calculations for superlattices with m=1,…,14 confirm the observed dependence of the E0 transition on the superlattice period. We further discuss our theoretical findings of type-II alignment for electrons and holes, which should be located within the GaP- and InP monolayers, respectively.