Measurement of collector-base junction avalanche multiplication effects inadvanced UHV/CVD SiGe HBT's

This paper presents measurements of the avalanche multiplication factor (M - 1) in SiGe HBT's using a new technique capable of separating the avalanch e multiplication and Early effect contributions to the increase of collecto r current with collector-base bias, as well as allowing safe measurements a t practical current densities. The impact of collector doping, current dens ity, Ge profile, and operation temperature are reported for the first time using measured and simulated results from a production quality UHV/CVD Sice HBT technology. Limitations of the technique in the presence of significan t self-heating are discussed. By turning on the secondary hole impact ioniz ation, we revealed the difference in impact ionization between strained SiG e and Si in the presence of the "dead space" effect, Despite its smaller ba ndgap, the compressively strained SiGe layer shows an apparent decrease in the secondary hole impact ionization rate compared to Si.