Abstract

While the speed at which a SEED device may be switched is limited fundamentally by carrier vertical transport times and RC effects, in a practical parallel processing system it is likely to be limited by the ratio of incident optical power and device switch energy. Since high speed SEED operation is desirable for a high processing rate, it is important that the device performance is not degraded at high incident power. One of the important mechanisms which result in this degradation is the build-up of a carrier density in the quantum wells (QWs). This carrier density weakens the excitonic absorption feature, resulting in a reduction of the reflectivity contrast ratio. In references [1] and [2] several QW structures were compared and the saturation effects were found to decrease as the sweep-out time [3] was reduced by either lowering or thinning the barrier between wells. An MQW consisting of 100Å GaAs wells and 35Å Ga_0.7Al_0.3As barriers was therefore developed in [1] and for this structure, at the intensities used in that work, no saturation effects were observed. We have extended the results by examining a similar structure and measuring the saturation of the responsivity and reflectivity at incident intensities up to 40kW/cm² (1400μW in a spot with 2.1μm 1/e²-1/e² intensity). Thermal effects were also observed. Using time resolved photoluminescence (TRPL) we have directly measured carrier sweep-out times and so have been able to calculate the carrier densities generated in the saturation experiments.

© 1993 Optical Society of America