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In this paper an asymptotic solution of the spherical harmonics equations describing the charge transport in semiconductors is found. This solution is compared with a numerical solution for bulk silicon device. We also indicate application of this solution to the construction of high field hydrodynamical models., Comment: 10 pages, LaTex, 3 figures (postscript) included in the text

In this paper the Boltzmann equation describing the carrier transport in a semiconductor is considered. A modified Chapman-Enskog method is used, in order to find approximate solutions in the weakly non-homogeneous case. These solutions allow to calculate the mobility and diffusion coefficients as function of the electric field. The integral-differential equations derived by the above method are numerically solved by means of a combination of spherical harmonics functions and finite-difference operators. The Kane model for the electron band structure is assumed; the parabolic band approximation is obtained as a particular case. The numerical values for mobility and diffusivity in a silicon device are compared with the experimental data. The Einstein relation is also shown., Comment: 15 pages, Latex, 5 figures (postscript) included in the text

A set of equations is derived from the Boltzmann kinetic equation describing charge transport in semiconductors. The unknowns of these equations depend on the space-time coordinates and the electron energy. The non-parabolic and parabolic band approximation are treated in detail. In these cases, the set of equations is equivalent to those obtained in the spherical-harmonics expansion. Stationary and homogeneous solutions are explicitly treated. In order to solve numerically the equations, a cut in the energy range is introduced. The modified model maintains the physical characteristics of the original equations. The solution of an asymptotic equation is found and compared to the numerical solutions., Comment: 26 pages, LaTex, 9 figures (postscript) included in the text