An investigation of carrier transport in thin silicon-on-sapphire films using MIS deep depletion Hall effect structures

Abstract

A deep depletion MIS structure has been used to obtain measurements of the carrier concentration and mobility variations through thin epitaxial films, (0·6–2 μm), of n-type silicon on sapphire substrates. Both the mobility and the net donor concentrations decrease in the direction of the sapphire interface. The room temperature mobility in the material close to the sapphire interface is shown to be limited by scattering at charged defects but in accumulation layers adjacent to the oxide interface a phonon scattering limitation is observed and a large proportion of the oxide interface scattering is shown to be specular. Under certain conditions shallow donor states can be generated at the sapphire interface in densities of the order of 10 12 cm −2. A new technique for measuring the energy distribution of fast interface states at the oxide interface in a film with nonuniform doping is described. The energy distributions obtained on the silicon-on-sapphire films investigated in the present work are very similar to those obtained in bulk silicon by earlier workers.