Optical Nonlinearities and Cross-Well Transport In Multiple Quantum Well Structures

Abstract

Multiple quantum well (MQW) semiconductors provide a number of nonlinear optical effects associated with well resolved, room temperature, exciton absorption features. Refractive nonlinearities arising from the saturation of the exciton by phase space filling, and the electric field induced quantum confined Stark effect (QCSE) can both be used to produce nonlinear characteristics at low laser powers. We use these effects to monitor optically created excess carrier dynamics in GaAs/AlGaAs MQW structures at room temperature on picosecond timescales. In particular, we have determined the time constants relating to cross-well carrier diffusion by thermionic emission from quantum wells, and tunnelling through 60Å barriers in the presence of an electrical field. Measurement of the temperature dependence of four wave mixing decay rates allows a study of the thermionic emission process, while the voltage dependence of the build up time of the cross­well photocurrent establishes the latter. The differential emission rates for both processes will be discussed.