Electron transport in silicon inversion layers at high magnetic fields and the influence of substrate bias

Abstract

Studies are reported of the conductivity in high magnetic fields of n-type inversion layers on the 〈100〉 surface of silicon. Previous studies of the conductivity minima occurring when the Ferrni level lies between two Landau levels have shown that conduction can occur by excitation to a mobility edge. At low temperatures, conduction is found to occur by hopping below the mobility edge with a temperature dependence given by σ 0 exp( 1 T ) 0.3 . The influence of substrate bias upon the conductivity spectrum has also been investigated. At moderate values of magnetic field (10–15 T) the conductivity maxima and minima change in both position and amplitude as a function of substrate bias. Additional splittings of the normal four-fold degeneracy also occur, and the energy levels of the valley and spin-split sub-bands are thought to re-order in some cases. At very high magnetic fields and large values of substrate bias it is found that the additional splitting is almost completely resolved so that eight peaks seem to appear within one Landau level.