STARK-LADDER TRANSITIONS IN GAAS/ALGAAS SUPERLATTICES

Electroreflectance measurements have been carried out in order to investigate Stark-ladder transitions in a GaAs(40 angstrom)/AlGaAs(20 angstrom) superlattice under various uniform electric fields, and compared with the transition energies calculated on the basis of a microscopic tight-binding description. The observed electroreflectance spectra in a wide range of energies (1.5-2.2 eV) shift in proportion to an applied electric field. The signals in the higher photon energy region (1.9-2.2 eV) indicate an existence of the transition from the spin-orbit split-off band in the valence band to the Wannier-Stark localization states in the conduction band. The assignment is supported by the tight-binding calculation. The resonant couplings of the localized states are also observed.