Current Fluctuations in the Acoustoelectric Steady State

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Abstract
A theoretical study of current fluctuations about the nonequilibrium acoustoelectric steady state of a piezoelectric semiconductor is presented. The two salient features of the observed noise are its large magnitude (typically ∼60 dB) above Nyquist noise and its spectral distribution (Lorentzian, with a low-frequency cutoff ∼20 Mc/sec). The former feature arises, in the present formulation, from the large fluctuations in the excess phonon concentration about its steady-state value. The low-frequency cutoff is given essentially by the temporal-gain constant for phonon growth. Physically, it represents the characteristic time for a fluctuation in drift velocity to produce a change in phonon concentration to which the drift velocity responds adiabatically. The final result for the spectral distribution bears a strong resemblance to that derived by Moore on the basis of a bunching theory.