Charge carriers, hopping motion

Fig. 21 A schematic view of the hierarchy of charge carrier hopping in a network of disordered conjugated polymer chains. 1 depicts ultra-fast motion within an ordered segment of the chain while 2 and 3 illustrate intra-and interchain hopping processes...

Similar conclusions on the character of conductance in the polycrystalline diamond films were derived in [33], The resistive intercrystallite boundaries can involve nonlinear resistance in polycrystalline diamond films moderately doped with boron [34]. Later, more sophisticated analysis [35-37] of the frequency dependence of impedance of polycrystalline diamond films resulted in a conclusion that at higher temperatures, in addition to the aforementioned electric conductance caused by the motion of free holes in the valence band, a second component of conductance manifests itself. The second component is due to the hopping of charge carriers between local traps possibly associated with the intercrystallite boundaries. 

Let us consider two-dimensional square lattice OABC (see Fig. 32), whereby microemulsion droplets occupy a number of sites. A selected separate charge carrier hosted by the droplet starts its motion from a position on the side OA at t = 0, and under the combined diffusion-hopping transport mechanism moves within the lattice OABC. It is understood that owing to this transport mechanism the trajectory of the individual carrier on the lattice OABC may be very complex and can even include loops. An example of such trajectories on the lattice OABC is shown in Fig. 33. 

Electronic conduction in inorganic melts can occur when atoms of the same kind in different oxidation states are present. Such systems exhibit an increased electrical conductivity with an exponential character of its temperature dependence, caused by a diffusion-like motion called hopping mechanism. The hopping mechanism is characterized by low mobility at elevated temperatures and the charge carrier is termed as a small-polaron. The mobility of the small-polaron is much lower compared to that of the carrier in a broad semi-conductor band. 

Except for these relatively few materials, most transition metal complexes exhibit properties more typical of semiconductors with conductivities usually less than 10" ohm" cm and a thermally activated conductivity behavior. The thermal activation energy, which is derived from plots of log charge carriers (as for example by direct band gap excitation in an intrinsic semiconductor) or from the carrier motion (as in systems where the conduction proceeds by a short range, thermally activated, hopping process). 

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