EFFECTS OF DOPING AND Ge FRACTION GRADING IN THE BASE ON THE BASE TRANSIT TIME AND EARLY VOLTAGE OF Si/SiGe HBTs

摘要

The base transit time τ_b and the Early voltage V_A for Si/SiGe HBTs with gradients of Ge fraction and doping in the base are studied. It is found that the retarding field caused by doping grading exhibits 40%-80% contribution to τ_b depending on the doping level near the emitter, V_A increases quasi-exponentially and τ_b decreases with the increase in gradient of Ge fraction in the base.