The effect of the base—collector potential spike on the common-emitter I—V characteristics of AlGaAs double-heterojunction bipolar transistors

Knee-shaped common-emitter current-voltage characteristics are always observed on AlGaAs double-heterojunction bipolar transistors and phototransistors when a potential spike is present at the base-collector heterojunction and the spike height is bias-dependent. This phenomenon is explained successfully using a new transport theory that is based on the current-balancing concept. In addition, many important heterojunction parameters, such as the potential spike height and the p-n junction position with respect to the metallurgical junction, can be extracted. These parameters provide a valuable means of evaluating the initial growth condition of the heterojunction during the epitaxial process. On the other hand, the transport mechanism of nonequilibrium electrons injected over the heterojunction is modeled using a simplified random-walk process. Its effect on the common-emitter current-voltage characteristics is presented.