Base Transit Time of Si/SiGe Heterojunction Bipolar Transistor

The base transit time of SiGe heterojunction bipolar transistor（HBT） is calculated and analysed. The effects on the intrinsic carrier concentration of the SiGe base and the electron mobility are considered which are caused by the base doping and Ge profile. The transit time of currents induced base（CIB） at the high current density is also considered. The results show that the box-triangular Ge profile with X<SUB<1</SUB</W<SUB<b</SUB<≈0.12 gives the minimum base transit time, Ge profile has little effect on the effective density of states and quite an effect on the electron mobility, and it has little effect on the base transit time whether the base doping profile is exponential or Gaussian.