A COMPARATIVE-STUDY OF THE KIRK EFFECT IN GAAS AND SI BIPOLAR JUNCTION TRANSISTORS

The Kirk effect in GaAs BJTs has been compared with that of Si BJTs us ing a PISCES-IIB simulator. The simulation results have shown that, du e to the high election mobility and velocity overshoot effect of GaAs, the Kirk current density of GaAs BJTs is about two times larger than that of comparable Si BJTs. It is shown that the saturation velocity m odel of the Kirk effect is very accurate for Si BJTs, but not for GaAs BJTs. A modified structure GaAs BJT with n+-n- collector layer, which is generally believed to have a higher Kirk current, was also studied . We have found for thal case that a retarding field is formed at the n+-n- interface and that the Kirk current does not increase at all.