Interface states in polymer metal-insulator-semiconductor devices

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 similar to 0.5 eV above. Annealing the devices under vacuum for several hours at 90 degrees C increases the concentration of the shallower traps to similar to 3x10(12) cm(-2) eV(-1), while decreasing the concentration of deep traps to similar to 1x10(10) cm(-2) eV(-1). Annealing improves the bulk hole mobility to similar to 1x10(-4) cm(2) V-1 s(-1) while reducing the field-effect mobility in MIS field-effect transistors (FETs) slightly to similar to 7x10(-3) cm(2) V-1 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. (c) 2005 American Institute of Physics.