NEUTRAL BASE RECOMBINATION AND ITS INFLUENCE ON THE TEMPERATURE-DEPENDENCE OF EARLY VOLTAGE AND CURRENT GAIN EARLY VOLTAGE PRODUCT IN UHV CVD SIGE HETEROJUNCTION BIPOLAR-TRANSISTORS/

We present the first comprehensive investigation of neutral: base reco mbination (NBR) in ultra-high vacuum/chemical vapor deposited (UHV/CVD ) SiGe heterojunction bipolar transistors (HBT's), and its influence o n the temperature characteristics of Early voltage (V-A) and current g ain-early voltage product (beta V-A). We show that a direct consequenc e of NBR in SiGe HBT's is the degradation of V-A when transistors are operated with constant-current input (forced-I-B) as opposed to a cons tant-voltage input (forced-V-BE). In addition, experimental and theore tical evidence indicates that with cooling, V-A in SiGe HBT's degrades faster than in Si bipolar junction transistors (BJT's) for forced-I-B mode of operation, Under the forced-V-BE mode of operation, however, SiGe HBT's exhibit a thermally-activated behavior for both V-A and bet a V-A, in agreement with the first-order theory, The differences in V- A as a function of the input bias and temperature for SiGe HBT's are a ccurately modeled using a modified version of SPICE, The performance o f various practical SiGe HBT circuits as a function of temperature, in the presence of NBR, is analyzed using this calibrated SPICE model.