Excitons in GaAs/(Al,Ga)As superlattices with coupled wells

Abstract

Various new electrooptic device concepts have recently been proposed which utilize the electronic energy band structures in semiconductor superlattices. The energy bands and excitons in superlattices have not received as much attention as those in quantum wells. A series of high-quality GaAs/(Al, Ga)As superlattice samples have been fabricated to have varying barrier widths using MBE. These samples have been analyzed by transmission electron microscopy to determine the layer thicknesses. Excitation spectroscopy at 5 K was employed to study the energy subband and exciton structures in superlattices. In thin barrier superlattices, well-to-well coupling significantly affects the miniband structures and excitonic states. We report here our observations of the spectral changes associated with coupling of the wells in superlattices. Minor peaks and bumps appeared in addition to the major heavy-hole and light-hole exciton peaks. Striking changes in these exciton spectra were detected with a small change (20 Å) in the barrier widths. From these structures, exciton binding energies in superlattices were derived and found to depend on the barrier layer width. Some of the minor peaks are attributed to the excitons formed at the Brillouin zone edge.