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-Al0.75Ga0.25As 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.