MODELING OF SMALL-SIGNAL RESPONSE AND ELECTRONIC NOISE IN SEMICONDUCTOR HIGH-FIELD TRANSPORT

We present a survey on the theoretical modelling of the small-signal r esponse and noise associated with velocity fluctuations in semiconduct or high-field transport. Because of the high values of the applied ele ctric field, current-voltage characteristics and electrical noise are found to deviate strongly from Ohm's law and Nyquist's relation respec tively. Accordingly, in the case of homogeneous (bulk) structures the field and frequency dependence of the differential mobility, diffusivi ty and electronic noise temperature are investigated within a rigorous microscopic approach which solves exactly the appropriate kinetic equ ations through analytical and Monte Carte techniques. Spectral functio ns in the frequency domain are obtained from their correspondent respo nse and correlation functions in the time domain. The subject is also analysed within a balance-equation approach which enables us to obtain simple analytical expressions which can provide a direct microscopic interpretation and can be applied to device modelling. For validation purposes calculations are applied to the relevant case of holes in Si and electrons in GaAs. In the latter material the presence of negative differential conductivity (Gunn effect) leads to interesting behaviou r of the small-signal response and noise spectra which are also invest igated for the simplest prototype of non-homogeneous structures, that is the n(+)nn(+) diode. The comparison between the different approache s so developed and between calculations and experiments is found to be quite good, thus providing a quantitative microscopic interpretation of the main features associated with small-signal response and fluctua tions in semiconductors under high-field conditions.