Electron lifetime measurements in MQW detectors: absorption and photoresponse saturation by a free electron laser

We measured the absorption and photoresponse saturation of GaAs/AlGaAs quantum wells as a function of the incident power. We used picosecond micropulses with a power density up to 10GW/cm ² delivered by a free electron laser. First, we compared the absorption in a sample with a bound-to-bound transition to the absorption in a sample with a bound-to-free transition, and found that the electron lifetime in the bound-to-bound transition is about four times shorter than for the bound-to-free transition. Then, we measured the photoresponse saturation in multi-quantum well detectors for different biases. We observed that the electron lifetime increases with the applied electric field from about 1 ps at zero field up to 10ps at 20kV/cm.