Base transport factor calculations for transistors with complementary error function and Gaussian base doping profiles

By taking account of the carrier mobility degradation at high impurity concentrations, the high-frequency base transport factor of an n-p-n germanium base transistor was computed numerically for different base doping levels. The doping profiles under consideration were Gaussian and complementary error functions. The base doping level adjacent to the emitter was optimized for minimum base transit time. The optimum values are 4×10¹⁷atom/ cm³for complementary error function profile and 2×10¹⁷atom/cm³for Gaussian profile. The effects of emitter barrier capacitance, base resistance, collector barrier capacitance, and the collector depletion layer on the overall frequency response of a junction transistor are also discussed.