Modeling of current gain's temperature dependence in heterostructure-emitter bipolar transistors

The temperature dependence of the current gain is investigated for GaAs-based heterostructure-emitter bipolar transistors (HEBT's). With the separation of the p-n junction and the heterojunction, the mechanism of hole injection from the base to emitter in the HEBT is different from that of a conventional HBT. Theoretical results demonstrate that the thermionic emission current plays an important role for the hole current which results in a smaller negative or even positive temperature coefficient for the current gain. Experimental data show that the base current for HEBTs is indeed dominated by thermionic emission as predicted. This finding indicates that the HEBT structure is the suitable choice for high power and high speed applications.