Electron trapping and inversion layer formation in photoexcited metal-insulator-poly(3-hexylthiophene) capacitors

Abstract

Photocapacitance measurements are reported on metal-insulator-semiconductor (MIS) capacitors employing polyimide (PI) or polysilsesquioxane (PSQ) as the gate insulator and poly(3-hexylthiophene) as the active semiconductor. By stressing devices into depletion while simultaneously irradiating with light of energy exceeding the semiconductor band gap, photogenerated electrons become trapped at the insulator/semiconductor interface or possibly in bulk insulator states. Additionally for the PSQ device, evidence is provided for the formation of a photogenerated inversion layer at the interface. The time dependence of electron detrapping in the PI case is similar to that observed for accumulation stress instability in organic MIS devices.