Electrorefraction associated with Wannier-Stark localization in strongly coupled three-quantum-well structures

Wannier-Stark localization of heavy holes and the associated refractive index changes in a strongly coupled GaAs-Al/sub 0.75/Ga/sub 0.25/As three-quantum-well structure have been investigated. Electroabsorption has been measured for TE polarization and the results compared with simulations performed by the exciton Green´s function method to reveal the dominant contributions to the differential absorption at low applied electric field. The refractive index changes calculated by Kramers-Kronig transformation are large compared with those arising from the quantum-confined Stark effect in conventional square quantum wells and are shown to derive from the emergence of only first-order ladder states due to the strong localization of heavy holes. Preliminary experimental confirmation of strong electrorefraction associated with heavy-hole state localization is obtained at 80 meV detuning. This effect is potentially useful for electrooptic device applications.