Gate-voltage-dependent Hall coefficient RH is measured in high-mobility field-effect transistors of polycrystalline dinaphtho [2,3-b: 2 ′, 3′ -f] thieno[3,2-b]thiophene films. The value of RH evolves with density of accumulated charge q, precisely satisfying the free-electron formula RH =1/q near room temperature. The result indicates that the intrinsic charge transport inside the grains is bandlike in the vacuum-deposited high-mobility organic-semiconductor thin films that are of significant interest in industry. At lower temperatures, even Hall-effect mobility averaged over the whole polycrystalline film decreases due to the presence of carrier-trapping levels at the grain boundaries while the free-electron-like transport is preserved in the grains. With the separated description of the intergrain and the intragrain charge transport, it is demonstrated that the reduction in mobility with decreasing temperature often shown in organic thin-film transistors does not necessarily mean mere hopping transport.
|Physical Review B - Condensed Matter and Materials Physics
|Published - 2010 Apr 12