Modeling of current transport and 1/f noise in heterojunction bipolar transistors

An analytic model is proposed to determine the effect of band offsets at he teroemitter interface on the current transport and 1/f noise in heterojunct ion bipolar transistors (HBTs). The proposed model uses the modified form o f drift-diffusion formalism, which requires that the net recombination rate s be proportional to the densities of other type carriers across the hetero interface. The numerical analysis of the current-voltage and 1/f noise char acteristics of Npn AlGaAs/GaAs HBT and npn GaAs BJT demonstrates that the r ole of band offsets at heteroemitter interface in the overall current trans port and 1/f noise is very important in HBTs at low forward biases. The jun ction resistance due to diffusing minority electrons is much stronger (weak er) at small (high) forward biases than that due to recombined electrons an d holes across the heteroemitted space charge region in both Npn AlGaAs/GaA s HBTs and npn GaAs BJTs. (C) 2000 Elsevier Science Ltd. All rights reserve d.