OPTICAL SPECTROSCOPY OF FIELD-INDUCED CHARGE IN POLY(2,5-DIMETHOXY-P-PHENYLENE VINYLENE) METAL-INSULATOR-SEMICONDUCTOR STRUCTURES

We have investigated metal-insulator-semiconductor structures fabricat ed with poly(2,5-dimethoxy-p-phenylene vinylene) as the active semicon ductor. In accumulation, we have observed three charge-related absorpt ion features at 0.7eV, 1.7eV and 2.0eV which scale in intensity with t he field-induced charge present in the device accumulation layer. We n ote that the two lower transitions are due to the same state, which ca n be associated with the presence of long-lived bipolarons, observed i n photo-induced absorption. We estimate a value for the optical cross- section associated with the bipolaron absorption at 0.7eV, of around 2 x 10(-15)cm2.