Electric field and charge distribution imaging with sub-micron resolution in an organic Thin-Film Transistor

Here we show how Stark spectroscopy, coupled with confocal microscopy, is able to directly map the electric field in an n-type Copper-Fluorinated Phthalocyanine Thin-Film Transistor (TFT) under different operating conditions. To this extent, we locally probe Electro-Reflectance, with a nominal spatial resolution better than 500 nm, exploiting the fact that the detected signal is directly proportional to the square of the local field on the probe volume. This electric field imaging technique has unique advantages because it is non-invasive, since it exploits low incident power and because it probes the existing field in the bulk rather than the surface. Combining the experimental data with numerical modeling, it is possible not only to reconstruct the space charge profile in the few-nanometer thick accumulation layer, but also to extract the AC electron mobility.