Effect of Interfacial Structure on the Transistor Properties: Probing the Role of Surface Modification of Gate Dielectrics with Self-Assembled Monolayer Using Organic Single-Crystal Field-Effect Transistors

Single-crystal field-effect transistors based on 2,3-dimethylpentacene have been used to probe the effect of surface modification of the insulating dielectric SiO2 layer on the transistor characteristics. Self-assembled monolayers (SAMs) of different chain lengths and functional groups were used to systematically modify the structure and property of the semiconductor/dielectric interface. The charge carrier mobility as a function of SAM used for surface modification was analyzed. The character of the terminal functional group, as well as the mechanic treatment (rubbing) of the monolayer, much influences the carrier mobility. Introduction of a polar end group (donor or acceptor type) decreases the mobility compared to a nonpolar end group. Prerubbing of the monolayer serves to increase the charge carrier mobility by a factor of 2-4-fold. The results are interpreted in terms of the orderliness of the monolayer which affects the contact at the monolayer/semiconductor interface, which in turn affects the trapping sites' density or the smoothness of the potential surface that the carriers experience while transporting along the interface.