Influence of Electron Scattering on Current Gain of Heterojunction Bipolar Transistor Operating in Coherent Regime

Abstract

We have analyzed the transport of electrons in the base of a heterojunction bipolar transistor operating in the coherent regime. The analysis is based on the Boltzmann transport equation for the one-electron distribution function. The influence of electron scattering on the transistor current gain in the frequency range beyond the usual cut-off frequency is included in the proposed model. It is demonstrated that the scattering of the electrons in the base region strongly affects the current gain of the heterojunction bipolar transistor in the extended frequency range. Conditions on the relationship between the electron transit times in the base and collector regions and electron scattering rate in the base, which are necessary for the implementation of the current gain beyond the usual cut-off frequency, are found.

Numerical and analytical modelling of electron transport in heterojunction bipolar transistors operating in the coherent regime

“…It is obvious that these results are quite different from the results of an analytical model which considers the electron transport in the base to be ballistic (Grinberg and Luryi 1993). Otherwise, these results are similar to the results of an analytical model that takes into account scattering of electrons in the base (Khrenov et al 1994). Thus, it is interesting now to compare the results of numerical simulation with the results of our previously developed analytical model.…”

“…The magnitude of the base transport factor |α B | as a function of the normalized frequency ωτ B is presented in figure 6 (hereafter τ B = W B m/p 0 ). The solid curve represents the results of the analytical model (Khrenov et al 1994) and the dashed curves correspond to the results of numerical simulation. The parameters of the HBT are as follows:…”

“…Unfortunately, this result can be considered as only an optimistic prediction because the ballistic transport is observed, in practice, only over a short distance. To make consideration of a coherent transistor more realistic we have developed an analytical model, which takes into account the scattering in the base (Khrenov et al 1994). It has been found that electron scattering in the base results in a considerable degradation of the base transport factor at frequencies below the reciprocal value of the base transit time.…”