The Role of Defective Regions Near the Contacts on the Electrical Characteristics of Bottom-Gate Bottom-Contact Organic TFTs

We studied, by 2D numerical simulations, the effects of poor semiconductor morphology near the source and drain contacts of BGBC-OTFTs. The variations of the electrical characteristics and of the path of the injected carriers in the transistor channel have been analyzed considering different defective regions, parameters (mobility, density of states) and contact thicknesses. The results showed that 100 nm wide defective regions can induce high contact resistance, resulting in large variation in the electrical characteristics. However, the typical S-shape in the low-Vds output characteristics is clearly observed only considering a combination of highly defected regions and Schottky barrier at the contacts. Furthermore, the simulations showed that most of the current is injected and extracted, at the source and drain contact, within a few nanometers from the semiconductor-dielectric interface. This explains the small influence of the contact thickness on the simulated electrical characteristics, at least for a contact thickness down to 10 nm.