Influence of quantum‐mechanical reflection at the emitter‐base spike on the base transit time through abrupt heterojunction bipolar transistors

A model to simulate electron transport through the base region of abrupt heterojunction bipolar transistors has been developed taking into account the finite probability for electrons in the base to tunnel through the emitter‐base spike back into the emitter. The average base transit time is calculated as a function of the emitter‐base voltage using the impulse response technique. For all biases, the average base transit time is found to be smaller than its value computed while neglecting the finite probability for electrons with energy below the emitter‐base spike to tunnel back into the emitter. For the case of an AlGaAs/GaAs structure, the average base transit time is found to increase with the forward emitter‐base voltage.