Impact of gate dielectric surfaces on carrier transport and injection in inverted-coplanar single-crystal organic transistors
Phys. Rev. Applied 24, 024038 – Published 15 August, 2025
DOI: https://doi.org/10.1103/8stj-n7cf
Abstract
The selection of gate dielectric materials is critical in organic thin-film transistors (OTFTs), as carrier transport occurs at the semiconductor/gate dielectric interface, directly impacting device performance. In this study, we systematically investigate how gate dielectric surfaces affect both carrier transport and injection at the contacts in model inverted-coplanar or bottom-gate bottom-contact (BGBC), single-crystal OTFTs. We examine ten gate dielectric surfaces with relatively high hydrophobicity and classify their influence into three groups based on chemical structure and surface energy: (i) fluorinated polymers, (ii) silane coupling agents (SCAs) without phenyl rings, and (iii) hydrocarbons containing phenyl rings. Among these, OTFTs using fluorinated polymers (low surface energy) exhibited the highest mobility and the smallest subthreshold swing (SS), while devices with high surface energy dielectrics displayed reduced mobility or degraded subthreshold characteristics. The transfer-line method (TLM) and Kelvin probe force microscopy (KFM) revealed that contact resistance is highly sensitive to the gate dielectric, with the highest resistance observed in devices using phenyl-containing hydrocarbons with high surface energy. Importantly, when the effects of contact resistance are excluded, all the devices exhibited high intrinsic mobility. These findings highlight the pivotal role of gate dielectric surface properties in determining both carrier transport and injection, offering key insights for optimizing the performance of BGBC-type OTFTs.
