ABSTRACT
We report on the electric transport properties of Si heavily doped with Sb at concentration just below the insulator-to-metal transition in the temperature range 1.9-3.0 K for current density J < 0.2 A cm-2. The change in the sign of the temperature dependence of the differential resistivity [Formula: see text] was observed: the d[Formula: see text]/dT is positive if J < 0.045 A cm-2 whereas it becomes negative at J > 0.045 A cm-2. The effect is explained assuming the exchange by electrons between the upper Hubbard band (UHB) and the conduction band. The obtained J dependencies of the activation energy, nonequilibrium concentration, mobility and scattering time of the conduction electrons correspond well to this hypothesis. The reason for charge instability is the Coulomb repulsion between electrons occupying states both in the UHB and conduction band. The estimated J dependencies of the conduction electrons lifetime and concentration of the D- states in the UHB strongly supports this assumption.
