Optical properties of semiconductor superlattice

Reflectivity measurements for a GaAs-AlAs superlattice and a Ga 0.5Al0.5As alloy were performed. Analyses of these results permit the determination of both refractive indices and absorption coefficients. The absorption edges for the alloy and superlattice are approximately 2 and 1.63 eV, respectively. A shift of 0.11 eV from the absorption edge of GaAs compares favorably with transport measurements showing that the lowest energy state in such a superlattice is about 0.1 eV above the bottom of the conduction band of GaAs.