The saturation characteristics of high-voltage transisitors

It is shown that the saturation characteristic of high-voltage NPvN transistors can only be explained by a lowering of the v-layer resistance due to conductivity modulation. A semi-quantitative model is developed which explains this modified saturation region. An experimental method of isolating the resistive portion of the external collector-base (CB) voltage is presented. The results verify that the CB junction may be forward-biased even when the characteristic seemingly indicates that the transistor is unsaturated. Data is also presented showing how variations in collector resistivity and thickness alter the saturation region.