We present an analytical modeling of the noise temperature associated with velocity fluctuations obtained in the framework of the linear-response theory around a steady state. The expressions are rigorously related to an eigenvalue expansion of the response matrix and are applicable to ohmic as well as to nonohmic ͑hot-carrier͒ conditions. Theory requires as input parameters the reciprocal carrier effective mass, the drift velocity, the carrier energy, the variance of velocity fluctuations, and the covariance of velocity-energy fluctuations as functions of the electric field in stationary and homogeneous conditions. The analytical results obtained for the case of holes in Si and electrons in GaAs at Tϭ300 K are validated by comparison with experiments.

We present analytical expressions for the differential-mobility spectra which are obtained from a linear analysis of the balance equations under stationary and homogeneous conditions. The expressions are rigorously related to an eigenvalue expansion of the response matrix and are applicable to ohmic as well as to non-ohmic conditions. The coefficients appearing in the formula can be calculated from the knowledge of three parameters as functions of the electric field, namely, the reciprocal effective mass, the drift velocity, and the average energy of the carriers. The theory is applied to the case of holes in Si at T= 300 K and validated by comparison with the results obtained by a direct numerical resolution of the perturbed Boltzmann equation. 0 1995 American Institute of Ph.ysics.

We present a detailed investigation of the transient transport regime in InP at room temperature based on an original method to solve numerically the coupled hot-phonon-hot-carrier time-dependent Boltzmann equations for the case of a steplike high dc electric field pulse. The method enables a study of the perturbation of the phonon distribution function induced by hot carriers and the corresponding modifications of the carrier distribution function. The numerical accuracy of the method is far beyond other existing methods, and, as a consequence, the time behavior of the main transport parameters can be resolved in great detail. The presence of nonequilibrium phonons is found to be responsible for an overall increase in the time duration of the transient regime. Modifications in the time evolution of the main transport parameters are also observed; in particular, the carrier drift velocity exhibits a second overshoot for electric fields near the threshold value for negative differential mobility. The sensitivity of the results to the value of the phonon relaxation time is also discussed.

We present two original methods which yield the small-signal response around the dc bias in bulk semiconductors, using direct numerical resolutions of the perturbed Boltzmann equation. The first method operates in the frequency domain. An ac sinusoidal electric-field perturbation superimposed to the dc field produces an ac perturbation of the distribution function which is computed at each frequency. The second method operates in the time domain. A step electric-field perturbation is superimposed at time t =0 to the dc field. The resulting perturbations of the distribution function and of the average velocity are then computed as functions of time. These methods are applied to the case of holes in silicon at T = 300 K under hot-carrier conditions and are used to compute the perturbed distribution function and the differential mobility spectrum.