Abstract
Ambipolar conduction is an essential and fundamental property in the application of the conventional inorganic complementary metal-oxide-semiconductor thin film transistors. Though in the past, the researchers usually regarded organic semiconductors as the materials that can only be capable of transport unipolar carrier. In fact, ambipolar conduction can be achieved through a proper interfacial modification in organic field-effect transistors. The main topic of this thesis is how to achieve a balanced and matched ambipolar conduction through two important interfacial modification: one is between the gate dielectric and organic semiconductor, the other is between the organic semiconductor and metal electrodes. As for the first interfacial treatment, there exists the silanol groups on the surface of the gate dielectric silicon dioxide layer, and the deep correlation between the presence of the silanol groups and the limit of the electron accumulation has been proved. Therefore, we introduce a polymer (e.g. polymethylmethacrylate) as the interfacial modified layer to lower the density of the electron traps, and facilitate the formation of N-channel conduction. As for the second interface, inserting an ultrathin nano-scaled interlayer (e.g. LiF, Cs2CO3) between organic semiconductor and metal electrode can further enhance the ambipolar conduction. If we control the thickness of this interfacial interlayer no more than 1 nm, and the presence of the ultrathin nano-scaled interlayer could not only facilitate the electron injection but it wouldn’t limit the p-channel conduction. Therefore controlling the thickness of the interlayer within a certain limit can achieve a balanced and matched ambipolar conduction. In addition to ambipolar characteristic, chapter 2 would discuss the factors that influence the unipolar conduction such as the intrinsic property of organic semiconductors, the ordering and alignment of organic molecules, the choices of high-κ dielectric, and the architecture of device structure. Besides, chapter 5 would investigate the bi-layer amipolar field-effect transistors, and compare the pros and cons with those of the single-component counterpart. In this studies, without complicated and multiple fabrication processes, balanced and matched ambipolar characteristic can be easily achieved merely through single active layer and two interfacial modifications. Utilizing this technique to fabricate the ambipolar transistors can immensely simplify the difficulties of fabrication and make the practical applications of ambipolar field-effect transistors more feasible and promising.