Nonohmic quasi-2D hopping conductance and the kinetics of its relaxation

The nonohmic properties of a quasi-2D hopping-conductance channel are studied. The channel is formed in a p-Si layer by a field effect in the region where the Fermi level crosses the impurity band. It is shown that the dependence of conductance σ on a longitudinal electric field E has a threshold character and obeys the law lnσ(E) ∝ E1/2. The dependences of the conductance of the quasi-2D channel on temperature and the electric field are satisfactorily explained using the concepts of nonlinear screening and of nonohmic properties of disordered systems with a random Coulomb potential. This mechanism of nonlinearity is confirmed by specific features of the mesoscopic fluctuations in the off-diagonal component of resistance, which reflect the reconstruction of a percolation cluster under the action of the longitudinal electric field. A long-term relaxation in conductance is observed during transition from a nonohmic to ohmic mode, which indicates that the system exhibits properties corresponding to electronic glass and that the current paths are significantly modified in a strong electric field.