A simple electrical approach to extracting the difference in bandgap across neutral base for SiGe HBT's

A simple general-purpose electrical approach to extracting the difference in bandgap across neutral base, i.e. ΔEG grade, for SiGe HBT's as well as Si BJT's with arbitrary Ge and dopant profiles, has been proposed. This approach is based on temperature dependence evaluation of combination of collector current, transconductance, and output conductance. In this work, it has been applied to fabricated RPCVD SiGe HBT's with the extracted values for ΔEG grade of 48 and 69 meV for two experimental splits, respectively. The bigger value for the latter has been ascribed to better confinement of boron profile within SiGe base layer owing to carbon incorporation which can effectively suppress boron out-diffusion.