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.