Gate voltage dependent mobility of oligothiophene field-effect transistors

TLDR

Organic field‑effect transistors using oligothiophene semiconductors of varying chain lengths have been fabricated and characterized, with gate‑voltage dependence possibly arising from trap‑limited transport or carrier‑concentration‑dependent mobility. The study investigates the origin of the gate‑bias dependence of mobility. The authors developed a method to estimate field‑effect mobility corrected for contact series resistance. Mobility rises nearly 100‑fold from quaterthiophene to octithiophene and increases quasi‑linearly with gate voltage.

Abstract

Organic field-effect transistors, in which the active semiconductor is made of oligothiophenes of various lengths, have been fabricated and characterized. A method is developed to estimate the field-effect mobility μ corrected for the contact series resistance. The mobility is found to increase by a factor of nearly 100 from quaterthiophene (4T) to octithiophene (8T). More importantly, μ increases quasilinearly with gate voltage. The origin of this gate bias dependence is discussed. One explanation could be the presence of traps that limit charge transport. Alternatively, the gate-voltage dependence is tentatively attributed to a dependence of the mobility with the concentration of carriers in the accumulation layer.