Bias dependent gain and speed mechanism in illuminated HBTs

A physics-based quantitative analysis of the illuminated HBT, with empirical verification, is discussed. A novel optical mechanism, internal photoconductivity, with large gain and bandwidth is described. The responsivity of the device can be considerably improved, 20-fold in this case, with a constant external base current biasing configuration as opposed to the constant base-emitter voltage case. The transient response of the HBT is discussed regarding incident optical power and biasing.