Device design and circuit modeling issues in ultrahigh vacuum/chemical vapor deposition SiGe heterojunction bipolar transistors

We discuss the physical basis, experimental results, and compact circuit modeling issues associated with neutral base recombination, germanium-ramp effects, and high-injection heterojunction barrier effects in graded-base, silicon-germanium heterojunction bipolar transistors. All three phenomena depend strongly on Ge profile shape and temperature, and are unaccounted for in conventional silicon bipolar transistor compact models such as SPICE.