Magnetoresistance in a two-dimensional impurity band

Abstract

The effect of a magnetic field perpendicular to the surface on the conductance of the two-dimensional (2D) Na⁺ induced impurity band in silicon inversion layers has been studied. The temperature dependence of the conductance at low fields (H < 5T) σ = σ_o′exp-(T_o′/T)^1/13, which is expected for variable range hopping in 2-D when the impurity wave functions are hydrogenic. At higher fields (H > 10T), σ = σ_oexp-(T_o/T)^1/12, which should result for Landau (Gaussian) impurity wave functions. In this high field regime we observe T_o = aH, where a depends only on the density of states at the Fermi level and fundamental constants. The density of states derived in this way is about an order of magnitude larger than the density of states inferred from earlier measurements and is even approaching the magnitude of the free electron density of states.