The photorefractive properties of semi-insulating AlGaAs-GaAs multiple quantum wells are described for the transverse Franz-Keldysh geometry with the electric field in the plane of the quantum wells. Combining the strong electroabsorption of quantum-confined excitons with the high resistivity of semi-insulating quantum wells yields large nonlinear optical sensitivities. The photorefractive quantum wells have effective nonlinear optical sensitivities of n2 103 cm 2 /W and a2/ao =: 10 4 cm 2 /W for applied fields of 10 kV/cm. Photorefractive gains approaching 1000 cm-' have been observed in two-wave mixing under dc electric fields and stationary fringes. The transverse Franz-Keldysh geometry retains the general transport properties and behavior of conventional bulk photorefractive materials. The resonant excitation of free electrons and holes in the quantum wells leads to novel behavior associated with electron-hole competition. We demonstrate that under resonant excitation of electrons and holes the device resolution is fundamentally limited by diffusion lengths but is insensitive to long drift lengths.

No abstract

Intervalley scattering of hot electrons during high-field transport in transverse-field photorefractive quantum wells induces a nonlocal optical response in which photoinduced changes in the refractive index are spatially shifted relative to the optical stimulus, providing an avenue for optical gain. We demonstrate that the onset of the photorefractive phase shift coincides with the onset of velocity saturation. This nonlocal response is the high-resistivity consequence in semi-insulating semiconductors of the Gunn effect mechanism.

No abstract

High-order spatial harmonics of photorefractive gratings are detected directly in multi wave mixing experiments in photorefractive AlGaAs/GaAs quantum wells operating in the Franz-Keldysh geometry. We have observed diffraction signals from the first-, second-, and third-harmonic refractive-index gratings. The quadratic electro-optic effect in the quantum wells second-spatial-harmonic grating.