Multiple triple-quantum-well active region for above-GaAs-bandgap reflection modulator

We have investigated a modulator structure based on GaAs/AlGaAs strongly coupled triple-quantum-wells (TQWs). Photocurrent measurements show sharper excitonic features with the TQW structure, while maintaining an equivalent Stark effect, compared to an alternate approach using multiple AlGaAs quantum wells and barriers with Al mole fractions of 0.06 and 0.3, respectively. With the goal of optimizing the speed of the device, we are currently investigating carrier dynamics in the TQW samples by means of picosecond laser pump/probe experiments. We have grown four samples by MBE containing identical intrinsic regions of multiple-TQWs, but with varying values of doping and/or thickness of the p-region for comparison. The results of picosecond pump/probe measurements that monitor the absorption recovery following an excitation pulse are compared to theoretical predictions of a model based on diffusive conduction of the carriers in the conductive layers, modified to include excess carrier transit times