Above barrier doublets in GaAs/AlxGa1−xAs superlattices

Doublets from optical transitions with energies greater than the barrier energy gap were observed by photoluminescence excitation spectroscopy in a series of GaAs/AlxGa1−xAs superlattices. The well width and the aluminum concentration in the barrier regions were fixed at 150 Å and 22%, respectively. The barrier widths ranged from 70 to 180 Å. The doublets arise from transitions between the first unconfined heavy-hole and conduction subbands. The separation of the doublet is found to be a sensitive function of the barrier width. It corresponds to the energy difference between the transition at the Brillouin zone center and at the Brillouin zone boundary along the superlattice growth direction. Good agreement was found between the experimental data and theoretical calculations. The sensitivity of the energy splitting to the width of the barrier provides a useful analytical tool in determining this quantity, in much the same way that the confined transition energies relate to the well width.