Hopping conduction diamond

Nanocrystalline diamond films also frequently show remarkable conductivity that is primarily attributable to the large portion of atoms situated in grain boundaries. The sp -hybridized carbon atoms generate electronic states within the diamond s bandgap. These lead, for instance, to the so-caHed hopping conductivity, that is, a conductance arising from a successive hopping from one state to the next. 

In Fig. 2a the change of slope in the resistivity curve for the natural diamond is interpreted (31) as hopping conductivity associated with activation energy 3, whereas all three conductivity mechanisms are believed (34) to be operative for the synthetic diamonds in Fig. 2b and c. For the diamond used to obtain Fig. 2c the data may also be fitted, in the temperature range 80 to 250 K, to Mott s formula (36) for variable range hopping. In this case... 

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. 

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