Large room-temperature optical nonlinearity in GaAs/Ga1−x AlxAs multiple quantum well structures

We report the first measurements of optical absorption saturation in GaAs/GaAlAs multiple quantum well (MQW) structures at room temperature near the heavy hole exciton peak. Linear absorption shows distinct exciton peaks at room temperature in the MQW and we deduce this is because the confinement increases exciton binding energy without increasing LO phonon coupling. This room-temperature MQW absorption also saturates more readily than that in a comparable GaAs sample; the measured saturation intensity is 580 W/cm2 with a recombination time of 21 ns in a MQW with 102-Å GaAs layers. From this we predict a nonlinear refraction coefficient n2∼2×10−5 cm2/W. This large nonlinearity should permit room-temperature optical devices compatible with laser diode wavelengths, materials and power levels.