Collector-base junction avalanche multiplication effects in advanced UHV/CVD SiGe HBTs

The collector-base junction avalanche multiplication factor (M-1) in SiGe HBTs is investigated using a new technique better tolerant to self-heating and collector-base leakage. The new technique provides higher accuracy at low current densities and enables M-1 to be measured at high current densities typically used in circuits. Comparisons with identically processed silicon control devices show that M-1 is not inadvertently increased by the incorporation of SiGe, despite its smaller bandgap. With cooling, M-1 first increases, and then saturates when T<117 K. A 2.3 V critical reverse CB voltage at which base current reversal occurs is observed down to 83 K, which is sufficiently high for today's bipolar and BiCMOS logic applications.