Abstract: The SiGe HBT DC models of and the analytic expressions for various currents with definite physical meanings are established, based on the solution to equations of drift and diffusion. The established current models are suitable for both large and small current injections. MEDICI is used to simulate the effects of Ge content and doping concentration on current density. The simulating results show that the decrease of the current gain is due to the decrease of the collector current and the increase of the neutral base recombination current caused by the increase of base doping cocentration. The effects of the collector current, backward hole injection current, neutral base recombination current and space-charge region recombination current on the current gain are also analyzed and discussed.

Key words: SiGe HBT, DC characteristics, similation