Above barrier PLE doublets in GaAs/Al sub x Ga sub (1-x) As superlattices.

Doublets from optical transitions with energies greater than the barrier gap were observed by photoluminescence excitation (PLE) spectroscopy in a series of GaAs/Al sub x Ga sub (1-x) As superlattices. The well width and the aluminum concentration in the barrier regions were fixed at 150angstroms and 22%, respectively. The barrier widths ranged from 70angstroms to 180angstroms. 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.