Gate Dielectric Chemical Structure−Organic Field-Effect Transistor Performance Correlations for Electron, Hole, and Ambipolar Organic Semiconductors

TLDR

Thiophene‑based n‑type semiconductors with similar film morphologies on various bilayer gate dielectrics provide a means to probe OTFT performance versus semiconductor‑dielectric interface relationships. The study presents a general approach to probe semiconductor‑dielectric interfacial chemistry effects on OTFT performance using bilayer gate dielectrics. The authors grow p‑, n‑, and ambipolar semiconductors on six bilayer dielectrics (polymers/HMDS on SiO₂) and characterize morphology with AFM, SEM, WAXRD, then perform transistor electrical measurements. Dielectric surface modifications strongly affect air‑sensitive n‑type OTFTs, causing large performance variations, while air‑stable n‑ and p‑type devices are largely unaffected; nonpolar polystyrene coatings on SiO₂ yield the highest mobilities (~2 cm²/V s) for air‑sensitive n‑type semiconductors, and electron trapping at silanol/carbonyl sites is identified as the main cause of mobility sensitivity.

Abstract

This study describes a general approach for probing semiconductor-dielectric interfacial chemistry effects on organic field-effect transistor performance parameters using bilayer gate dielectrics. Organic semiconductors exhibiting p-/n-type or ambipolar majority charge transport are grown on six different bilayer dielectric structures consisting of various spin-coated polymers/HMDS on 300 nm SiO(2)/p(+)-Si, and are characterized by AFM, SEM, and WAXRD, followed by transistor electrical characterization. In the case of air-sensitive (generally high LUMO energy) n-type semiconductors, dielectric surface modifications induce large variations in the corresponding OTFT performance parameters although the film morphologies and microstructures remain similar. In marked contrast, the device performance of air-stable n-type and p-type semiconductors is not significantly affected by the same dielectric surface modifications. Among the bilayer dielectric structures examined, nonpolar polystyrene coatings on SiO(2) having minimal gate leakage and surface roughness significantly enhance the mobilities of overlying air-sensitive n-type semiconductors to as high as approximately 2 cm(2)/(V s) for alpha,omega-diperfluorohexylcarbonylquaterthiophene polystyrene/SiO(2). Electron trapping due to silanol and carbonyl functionalities at the semiconductor-dielectric interface is identified as the principal origin of the mobility sensitivity to the various surface chemistries in the case of n-type semiconductors having high LUMO energies. Thiophene-based n-type semiconductors exhibiting similar film morphologies and microstructures on various bilayer gate dielectrics therefore provide an incisive means to probe TFT performance parameters versus semiconductor-dielectric interface relationships.