Visualization of induced charge in an organic thin-film transistor by cross-sectional potential mapping

Kelvin probe force microscopy was applied to the cross-sectional potential imaging of a working organic thin-film transistor (OTFT). The bottom-contact-type OTFT with an active layer of copper-phthalocyanine (CuPc) was cleaved and internal potential distribution of its channel region was visualized. The potential distribution on the cross section changed depending on the applied drain and gate voltage. Horizontal potential distribution in the semiconductor film from source to drain direction was roughly consistent with the results of surface potential imaging previously reported. Vertical potential distribution from bottom (gate) to top (CuPc film) showed that a potential peak appeared along the semiconductor/insulator interface when a negative voltage was applied to the gate. The charge injection process is discussed based on the visualized potential peak at the interface.