Charge variable range hopping

Fig. 14 A comparison of different approaches to describe the charge carrier mobility in a Gaussian-type hopping system as a function of the normalized concentration of the charge carriers, (a) Full curves are the result of effective medium calculations [100] while symbols are computer simulations [96], (b) Full curves are calculated using the variable range hopping concept [101], symbols are the computer simulations. From [100] with permission. Copyright (2007) by the American Institute of Physics...

Charge transport in the accumulation channel is described by the percolation model [24] based on thermally activated tunneling of holes between localized states in an exponential density of states, described in Section 13.2.2. In the accumulation regime this Variable Range Hopping (VRH) model yields a gate-voltage dependent field-effect mobility of the form ... 

Another characteristic feature of disordered systems is the variable range hopping (VRH) mechanism to the electrical conduction, which is observed on the nonmetallic side of the M-NM transition at low temperamres. This arises from the hopping of charge carriers between localized states, or impurity centers. Hence, the phenomenon is also known as impurity conduction. Experimentally, it is indicated by characteristic temperature dependency to the d.c. conductivity. Eor three-dimensional systems with noninteracting electrons, the logarithm of the conductivity and are linearly related, in accordance with the equation given by Mott (Mott, 1968)... 

As follows from the detailed kinetic analysis of this scenario [13,15], the model of variable-range hopping allows quite accurate predictions of both sequence and distance dependencies for the efficiency of charge transfer through stacks with various combinations of base pairs. This, in turn, provides reasonable estimations of the distance scale for the... 

The random disorder results in an increased conductivity in these materials, due to the absence of electrostatic forces which would lead to a charge ordered state. The disorder however leads also to electron localization and hopping conduc-tion the combination of the two sets a limit to S lOOffi. cm in this class of salts, with variable range hopping occuring at low temperatures. 

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