ENHANCED DETECTION BANDWIDTH FOR OPTICAL DOPPLER FREQUENCY MEASUREMENTS USING MOVING SPACE-CHARGE FIELD EFFECTS IN GAAS MULTIPLE-QUANTUM WELLS

Moving space charge field (photo-emf) effects are observed in standard and low temperature grown GaAs multiple quantum well (MQW) samples in which de photocurrents are generated by constant speed moving optical interference patterns. Experiments reveal an enhanced detection bandw idth for optical doppler frequency measurements compared to previously studied bulk II-VI and III-V materials due to the higher quantum effi ciency and optical absorption of GaAs MQWs, in spite of their reduced carrier mobility-lifetime product values resulting mainly from the sig nificantly shorter free carrier lifetimes. The high defect density of low temperature grown MQWs can also yield large field-of-view and, for optical ultrasound detections, high cutoff frequency. (C) 1997 Americ an Institute of Physics.