Experimental and Numerical Investigation of Contact Doping Effects in Dinaphthothienothiphene Thin-Film Transistors

Contact doping effects in p-channel dinaphthothienothiphene (DNTT) thin-film transistors with a bottom-gate, top-contact configuration were investigated with both experimental and numerical approach. Characteristic variation in transistor parameters such as the gate threshold voltage and the field-effect mobility for devices with various channel lengths was suppressed by the contact doping with tetrafluorotetracyanoquinodimethane (F₄TCNQ) as an acceptor dopant. The gate-voltage dependence of contact resistance and channel resistance was also evaluated separately to examine the contact doping effect in detail. In addition, device simulation considering a Schottky barrier at a metal/semiconductor interface successfully reproduced the experimental current–voltage characteristics by using a hole concentration of the active DNTT layer in the order of 10¹⁷ cm⁻³, which was estimated by capacitance–voltage measurement for a metal/insulator/semiconductor capacitor structure. This study suggests the importance of establishing both the carrier doping and carrier concentration measurements toward realizing practical applications of organic transistors.