High-frequency noise analysis of Si/SiGe heterojunction bipolar transistors

A novel approach to the noise of bipolar transistors at medium and high frequencies is developed and applied to Si/Si1- x Gex/Si heterojunction bipolar transistors. It is closely related to the technological process and it allows numerical HF noise prediction and optimization. For medium frequencies analytical expressions for minimum and optimum noise figure are derived. To obtain the noise figures at higher frequencies the time-dependent drift-diffusion equations are solved by using a two-dimensional device simulation code. The dependence of the noise figure on base doping and Ge profile is discussed.