Quantitative analysis of Si/GexSi1-x/Si heterojunction bipolar transistors with linearly graded Ge profile

A new experimental methodology for the analysis of Si/Ge_xSi_1-x/Si HBT yields quantitative values for the important transistor parameters, such as the energy gap reduction and the built-in electric field due to Ge, and the minority-carrier base diffusion length, lifetime and transit time. The method also enables a charge-control analysis of the base current to be made. A demonstration is presented for a GeSi heterojunction bipolar transistor with a linearly-graded Ge profile in the base. The methodology can be extended for arbitrary material composition and doping profile in the base.