Temporal response characteristics of a In/sub 0.53/Ga/sub 0.47/As/InP quantum well phototransistor

An investigation of multiple-quantum-well heterojunction phototransistors with InGaAs/InP quantum wells in the collector and InGaAsP base is discussed. The design of the structure ensures that light is absorbed only in the quantum-well region, thus providing a way to study the correlation between quantum well and phototransistor carrier dynamics. Moreover, since the operation of a n-p-n phototransistor is governed by hole injection into the base, the transient behavior of the device reflects the hole dynamics in the multiple-quantum-well region. The response of the device to picosecond optical pulses shows strong dependence on bias conditions: from device response determined by minority carrier recombination time ( approximately 2 ns) at high base-emitter bias, to current time constant dominated response ( approximately 50 ps) at low base-emitter bias. The field dependent escape times of carriers from the quantum wells under different bias conditions are obtained (10-100 ps) and are seen to affect the risetime of the transistor to pulsed photoexcitation.<
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