Dynamic Infrared Electro-Optic Response of Soluble Organic Semiconductors in Thin Film Transistors

TL;DR

This study employs a frequency-dependent electro-optic method to measure hole mobility in small molecule organic semiconductors within thin film transistors, revealing frequency-dependent behaviors and deviations at high frequencies related to dielectric and contact properties.

Contribution

It introduces a novel electro-optic measurement technique for organic FETs and analyzes frequency-dependent charge dynamics in different dielectric environments.

Findings

Measured hole mobility in organic semiconductors using infrared electro-optic response.

Observed deviations at high frequencies in alumina dielectric FETs, indicating contact impedance effects.

Provided insights into charge flow and spatial charge distribution in organic thin film transistors.

Abstract

We use a frequency-dependent electro-optic technique to measure the hole mobility in small molecule organic semiconductors, such as 6,13 bis(triisopropylsilylethynyl)-pentacene. Measurements are made on semiconductor films in bottom gate, bottom contact field-effect transistors (FETs.) Because of the buried metal layer effect the maximum response, due to absorption in the charge layer, will be for a dielectric film ~ 1/4 of a wavelength (in the dielectric) (e.g. ~ 1 micron thick in the infrared.) Results are presented for FETs prepared with both spin-cast polymer and alumina dielectrics prepared by atomic layer deposition. At low frequencies the results are fit to solutions to a non-linear differential equation describing the spatial dependence of flowing charge in the FET channel, which allows us to study multiple crystals forming across one set of drain-source contacts. FETs prepared on alumina dielectrics show interesting deviations from the model at high frequencies, possibly due to increased contact impedance.