HIGH-FREQUENCY NOISE OF BIPOLAR-DEVICES IN CONSIDERATION OF CARRIER HEATING AND LOW-TEMPERATURE EFFECTS

We derive an expression for the high-frequency spectrum of thermal cur rent noise in bipolar devices from quantum mechanical linear response theory. This expression relates the noise spectrum to local small-sign al quantities. It is independent of geometry and holds for arbitrary s pace-dependent carrier temperatures including low ones. The general re sult is applied to pn-diodes and bipolar transistors. In the isotherma l case and for not too low temperatures the expressions known from the literature can be reproduced. We apply our approach to Si1-xGex heter ojunction bipolar transistors in order to calculate the minimum noise figure at high frequencies. The electron heating in the collector is s hown to have a noticeable influence on the noise figure at very high f requencies.