Mott Variable Range Hopping VRH Model

We are now in a position to consider conduction models, after which we may look at some of the experimental observations that these models attempt to predict. One of the first models to be considered for CPs, primarily because it appeared to apply to disordered conventional semiconductors and CPs were considered disordered. 

The Mott VRH model agrees well with experiment for moderate temperatures and doping levels for CPs, and is found to apply in many cases to materials such as amorphous carbon as well [176]. Indeed, many recent studies on a variety of CPs, such as those correlating ESR spins with dc conductivity [177], appear to confirm the Mott VRH model. Although there are two fitting parameters, and T , the latter 

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First, at low dopant concentrations, both PPY and PAc act as insulators. At a relatively high temperature, electronic transport can be described by Mott variable-range-hopping (VRH) model. Resistivity is a function of temperature that follows ... 

As the first insulating/semiconducting higher boride series, the electrical transport of these compounds has been carefully investigated (e.g. Slack et al., 1977 Golikova, 1987 Werheit et al., 1991). The temperature dependence of the resistivity p follows the dependency of Mott s variable range hopping (VRH) model for 3 dimensional systems (Mott, 1968 Efros and Shklovskii, 1985), where... 

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