Analytical Base-Collector Heterojunction Capacitance Model Including Collector Current Effects

The base‐collector heterojunction space‐charge‐region capacitance of double heterojunction bipolar transistors is treated. This capacitance cannot be modeled as the conventional heterojunction depletion capacitance because it is heavily influenced by the collector current, which is neglected in the depletion capacitance model. The analysis includes heterojunction effects as well as high current phenomena such as base pushout and space‐charge‐limited flow. Large discrepancies are found when comparing the present model with the depletion model at high current densities. Comparison of the base‐collector junction capacitances calculated from a single heterojunction bipolar transistor and a double heterojunction bipolar transistor is also included