Optical transitions in very short period GaAs-AlAs superlattices

The current understanding of the optical transitions in very short period superlattices is briefly reviewed. Also reported are photoluminesence spectroscopic studies on a series of very short period (GaAs)_n-(AlAs)_n superlattice samples (n = 1, 2, 3 and 4) grown by molecular beam epitaxy. The results and discussions are mainly concerned with the ordering of the X_z and X_x,y valleys, the valley mixing induced by superlattice potential and interface potential, the excitation process and the phonon-assisted transitions.