We present results obtained from a study of the admittance of metal-insulator-semiconductor capacitors formed from regioregular poly(3-hexylthiophene). Data obtained over a range of applied bias and frequency can be explained by the presence of a distribution of trapping states at the insulator∕semiconductor interface as observed in metal-oxide-silicon capacitors. We also observe a depletion-bias instability in the threshold voltage, $V_T$ , that is consistent with negative charge trapping at the insulator∕polymer interface. The shift can be relaxed by illumination with bandgap light, $\lambda =550\mathrm{nm}$ , suggesting that the instability arises from an electronic process.

The admittance of polymer metal-insulator-semiconductor (MIS) capacitors has been measured as a function of frequency and applied voltage. The results reveal the presence of hole trapping states at the interface of the polysilsesquioxane insulator and the poly(3-hexylthiophene) semiconductor. The states appear to be distributed in two bands: one close to the equilibrium Fermi level at the semiconductor surface, the other $\sim 0.5\mathrm{eV}$ above. Annealing the devices under vacuum for several hours at $90°\mathrm{C}$ increases the concentration of the shallower traps to $\sim 3\times {10}^{12}{\mathrm{cm}}^{-2}{\mathrm{eV}}^{-1}$ , while decreasing the concentration of deep traps to $\sim 1\times {10}^{10}{\mathrm{cm}}^{-2}{\mathrm{eV}}^{-1}$ . Annealing improves the bulk hole mobility to $\sim 1\times {10}^{-4}{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ while reducing the field-effect mobility in MIS field-effect transistors (FETs) slightly to $\sim 7\times {10}^{-3}{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ . Although the concentration of interface states is sufficiently great to account for gate-bias-induced threshold voltage instability in MISFETs, their associated time constants are much too short to explain the long term nature of the instability.

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.