The temperature dependence of the dc characteristics of silicon germanium bipolar transistors

Silicon germanium bipolar transistors provide excellent high frequency perf ormance within the context of silicon, encroaching dramatically on III-V se miconductor's territory. Applications or the technology, however, will requ ire the performance specifications with regard to the temperature range of operation. Using devices accessible from a BiCMOS technology, adapted to in corporate SiGe, we have measured the temperature dependence of properties s uch as the de gain, ideality factors, and V-BE at various base current leve ls, from 100 to 450 K. The ideality factors are close to unity above 250 K but greater than 2.5 at 100 K. We suggest that tunneling at the emitter per imeter can account for the high base ideality factors at low current and lo w temperature. Our data show a decrease in the gain with increasing current and temperature in normal operating ranges---devices with "box" Ge profile s in the base layer do not have this feature. This is important in preventi ng thermal runaway in power transistors, and may remove the necessity of em itter ballast resistors and provide higher power-added-efficiency in an amp lifier block. We also show that the gain-Early voltage product is roughly l inear with 1/T above ambient temperature. (C) 2000 American Vacuum society. [S0734-2101(00)04802-8].