CONDUCTION ELECTRON-GAS DIELECTRIC FUNCTION OF MULTIVALLEY SEMICONDUCTORS - AN APPLICATION TO SILICON

The dielectric function of multivalley conduction electron systems is studied taking into account both the intravalley and the intervalley m atrix elements. A direct application is performed for the six-valley s ilicon case. It is shown that the dielectric function takes the form o f a sum of Lindhard-type terms, each one related to a pair of valleys. Analytical approximations for the static and dynamical cases are prop osed. It is shown that while in the static case the intervalley contri butions are negligible, in the dynamical case they lead to composite p lasma dispersion of acoustic type for q --> 0. New analytical approxim ate plasma dispersion formulae are presented and it is shown that the acoustic behavior can be interpreted within a two-component plasma mod el where to the intervalley contributions an effective mass lighter th an the band mass is associated.