Abstract

The spatial confinement of carriers in semiconductor quantum well structures leads to resolvable excitonic features at room temperature. Saturation of these due to phase space filling gives rise to a very large non-linear refractive index [1,2]. We have used this non-linearity in GaAs/AlGaAs multiple quantum wells in two separate degenerate four wave mixing configurations. The two arrangements, forward travelling and counter-propagating (see fig.1), produce transient phase gratings across and parallel to the plane of the wells respectively. Time resolved measurements of the decay of these gratings allow comparison of intra-well and cross-well contributions to carrier diffusion, which is highly anisotropic, and reveal decay rates dependent upon the angle of the sample to the normal. In addition such experiments give carrier relaxation times and the intensity at which the excitonic non-linear refraction starts to saturate.

© 1988 Optical Society of America