Band-to-band tunneling in vertically scaled SiGe:C HBTs

A nonideal base current component with negative differential resistance is observed at low injection on Gummel characteristics of high-speed SiGe:C bipolar transistors. The temperature dependence of this effect and the influence of emitter-base engineering on its magnitude are described. The results point to band-to-band tunneling in the emitter-base junction as the physical origin of this phenomenon.