Early Voltage and Current Gain of Si1-yGey Heterojunction Bipolar Transistor

Closed form analytical models were derived for Early voltage (VA) and common emitter current gain (β) for Si1-yGeyHeterojunction Bipolar Transistor (HBT). Field dependent mobility, doping dependent mobility, band gap narrowing (BGN) effect (due to both heavy doping and presence of Germanium content in the base) and velocity saturation effects were considered in these models. The derived models are applicable for uniform, exponential and Gaussian types of base doping profiles and trapezoidal, triangular or box germanium profiles.The variations of VA, β, intrinsic carrier concentration, diffusivity and electric field in the base region with the variation of germanium mole fraction were studied. The results obtained by these analytical models were compared with the results available in the literature and found in good agreement.