EXTENDED PHONON-SCATTERING MECHANISM AS AN EXPLANATION FOR LOW MOBILITY IN HIGHLY CONCENTRATED ELECTRON LAYERS AT SILICON INTERFACES

Mobility data for electrons in very-high-density accumulation layers at the Si(111)/polymer-electrolyte interface are presented which identify phonons as the major scattering source even in this density range. Next we present a revised treatment of usual acoustic-phonon and intervalley-phonon scattering mechanisms including the case of a degenerate Si(111) two-dimensional electron gas. However, this approach overestimates the experimental 100 cm2/V s mobilities by a factor of 510. Hence, a new extended scattering mechanism by acoustic phonons is proposed which accounts for these low mobilities as well as for those observed in concentrated accumulation and inversion layers at the Si/SiO2 interface around room temperature. This is done by using the kp expansion of the phonon-scattering matrix element one order higher than the usual deformation-potential mechanism in order to establish a simplified expression which is further adapted to the two-dimensional case. A simple interpretation is proposed, consisting of a deformation-induced displacement of the position of valley minima in reciprocal space. Finally, the order of magnitude of this new mechanism is explained by considering the vicinity of the conduction-band minima relative to the Brillouin-zone edges. © 1990 The American Physical Society.