Anomalous Photocurrent Generation in Transistor Structures

It has been previously reported that, at relatively modest dose-rates (~109 rad/sec), certain transistor types exhibit an anomalous primary photocurrent response which results in serious departures from the commonly assumed linear dose-rate dependence. This paper presents additional experimental evidence concerning the anomalous photocurrent problem and develops a model which explains the observed data in terms of carrier generation and transport processes within the device. The analysis and supporting experimental evidence shows that the observed phenomenon is the result of base-emitter junction breakdown. This breakdown is induced by transverse photocurrent flow in the active base region and causes the device to assume a common emitter configuration wherein the primary photocurrent is amplified by the device gain.