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Applied Physics Letters

Photorefractive gain in GaAs under a dc electric field

Duncan T. H. Liu, Li‐Jen Cheng, Mann-Fu Rau, Faa-Ching Wang

Published Oct 10, 1988• 20 citations
Publisher

Abstract

We report the first observation of a photorefractive gain coefficient as high as 2.6 cm−1 in the undoped liquid-encapsulated Czochralski-grown GaAs crystals at 1.06 μm under a dc electric field of 13 kV/cm without using the moving grating technique. The absorption coefficient of the crystals used is 1.3 cm−1, showing that a net gain has been achieved. This measured gain coefficient is close to the predicted theoretical value.

DOI
10.1063/1.99981

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Journal of the Optical Society of America B•May 1, 1995•3 citations
We report the first observation of a photorefractive gain coefficient as high as 2.6 cm−1 in the undoped liquid-encapsulated Czochralski-grown GaAs crystals at 1.06 μm under a dc electric field of 13 kV/cm without using the moving grating technique. The absorption coefficient of the crystals used is 1.3 cm−1, showing that a net gain has been achieved. This measured gain coefficient is close to the predicted theoretical value.
We have observed two-wave mixing in semi-insulating AlGaAs/GaAs multiple quantum well structures at wavelengths near the exciton absorption. The photorefractive index changes are caused by the Franz–Keldysh effect on quantum-confined excitons. Photorefractive gains larger than 200 cm−1 are obtained for the first time at wavelengths near 836 nm using stationary fringes and dc applied fields up to 5 kV/cm. The direction of energy transfer between the two beams is determined by the direction of applied electric field.
We have observed two-beam coupling gain (0.273 cm−1) that exceeds absorption (0.145 cm−1) in InP:Fe without applying an external field at λ=1.32 μm. Measurements of the gain coefficient as a function of grating spacing fit the photorefractive theory for simultaneous electron-hole transport, with the effective density of traps NE = (3.86 ± 1.1)NE=(3.86±1.1)× 1015 cm−3 and ξ, the factor that accounts for competition between electrons and holes, equaling −0.729±0.026. Absorption measurements, combined with the photoionization cross sections of electrons and holes, confirm these results. The agreement between theory and experiment suggests how to choose impurity concentrations that optimize net gain.
The theory of photorefractive grating formation in a semi-insulating GaAs/AlGaAs multiple-quantum-well structure (MQWS) with an electric field applied across the layers and for counterpropagating writing beams is presented. The gain and the response time demonstrate a resonant behavior with respect to variations in both the applied field and the light’s wavelength. For a semi-insulating MQWS such an interaction geometry could provide the highest two-wave mixing gain, as much as 104 cm−1, which exceeds the linear absorption.