Direct imaging of conductivity in pentacene field-effect transistors by a near-field scanning microwave microprobe

A near-field scanning microwave microprobe (NSMM) is employed to visualize the carrier distribution in the active layer of an organic field-effect transistor (OFET). Experiments using this technique with a pentacene OFET reveal changes of the conductivity profiles in the channel which arise from the development and exhaustion of an accumulated charge region. Electric field profiles that are visualized by using the electric field induced optical second harmonic generation (EFISHG) method, verify the results. NSMM is a powerful tool, and in combination with EFISHG will provide a way to directly probe carrier transport.

3D near-field microwave images from the 50 μm channel of a pentacene field-effect-transistor at various negative drain–source, Vds and gate–source, Vgs voltages. Voltages are applied to the drain and gate electrodes with the source electrode grounded.Figure optionsDownload as PowerPoint slideResearch highlights
► We visualized the conductivity profiles in the active layer of a pentacene organic field-effect transistor (OFET) by a near-field scanning microwave microprobe (NSMM) and by the electric field induced optical second harmonic generation (EFISHG) method.
► The conductivity of pentacene active layer of OFET was investigated by measuring the microwave reflection coefficient S11.
► The resulting spatial and lateral resolutions of mapping were about 2 μm and 5 μm, respectively, however, the NSMM incorporating with a commercial AFM probe-tip and 2D PZT scanner is able to map with an effective resolution of up to 50 nm.
► NSMM experiments in combination with EFISHG measurements could be an effective method for directly characterizing the I–V and C–V characteristics of materials on a microscopic scale.
► We anticipate that the use of this microwave method will be of great help for the understanding of carrier transport in organic materials, including bio-materials and molecules.