A theoretical analysis of velocity fluctuations in semiconductors is presented both in steady-state and in transient-regime conditions. Results obtained from a Monte Carlo procedure are shown for Si and GaAs. It has been found in particular that (i) off-diagonal contributions to the autocorrelation function must be taken into account; (ii) the convective contribution is positive; (iii) a long tail in the autocorrelation function, due to intervalley fluctuations, may be present; (iv) the negative part in the longitudinal autocorrelation function is due to the thermal contribution and is related to the increasing efficiency of the scattering mechanisms at increasing energies. Furthermore, the transport transient and the correlation transient are analyzed separately but simultaneously through the two-time autocorrelation function, and their effects on the results are discussed for real cases.

• Received 6 December 1983

DOI:https://doi.org/10.1103/PhysRevB.29.5739