Optical EngineeringTheoretical studies on the transient behavior of high electron mobility phototransistors
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The transient behavior of a high electron mobility phototransistor has been calculated theoretically, where radiation is allowed to fall within the gaps between source, gate, and drain and the gate behaves as an opaque material. The parameters calculated are the threshold voltage, drain-source current, and transconductance of the device as functions of time. It is observed that when the light is turned on, the parameters reach the steady-state value at around 40 ps, and when the light is turned off, they reach their dark values at around 300 ps. In the turned-on case, it is the optical relaxation time that controls the behavior, and in the turned-off case it is the photovoltage across the heterointerface, which decreases linearly with time.