Charge modulated reflectance topography for probing in-plane carrier distribution in pentacene field-effect transistors

By using charge modulated reflectance (CMR) topography, we showed that the in-plane carrier distribution in pentacene field-effect transistors (FETs) can be directly probed under the device operation. Further, we showed that the observed CMR signal is attributed to a decrease in the electron population in pentacene highest occupied molecular orbital level, caused by hole injection. The signal profile along the FET channel strongly depends on the bias conditions. The carrier density decreases monotonously along the channel from the source to the drain in the saturated region; this decrease is interpreted by a simple model based on interfacial accumulated charge transportation.