Thermionic Injection and Contact Resistance Model for Bottom Contact Organic Field-Effect Transistors

The presence of high contact resistance at the metal–organic semiconductor interface is a crucial issue in performance of organic field-effect transistors. In this report, an analytical expression of gate-voltage-dependent contact resistance has been derived for bottom contact organic field-effect transistor geometry. In this derivation, the thermionic injection mechanism, gate-voltage-dependent carrier mobility in the vicinity of the metal–organic semiconductor interface, and the Poole–Frenkel barrier lowering effect of the injection barrier have been taken into account. The developed analytical expression has been fitted with published data of a pentacene-based organic field-effect transistor. From the fit, hopping site density, interfacial charge density, and maximum mobility, near metal–organic semiconductor contact has been extracted. Also, numerical plots for output and transfer characteristics are plotted.