CHARGE INJECTION, ELECTRIC-FIELD MODULATION AND SPECTROSCOPY OF CHARGED STATES OF FULLERENE IN METAL-INSULATOR-SEMICONDUCTOR DEVICES

we have studied Metal-Insulator-Semiconductor (MIS) devices with fulle rene as the active semiconductor. We have made impedance analysis meas urements on these devices and we use these to characterise electrical transport in fullerene and the interfaces with insulators and metals. We have measured the modulation of the optical transmission through th e devices with gate voltage. We see a strong field-dependent modulatio n of the dipole-allowed transitions. We observe also optical transitio ns due to charges injected into the fullerene layer when we use C60/C7 0 mixtures. With pure C60 we see features related to charge injection only when the devices are exposed to illumination above the band gap. The positions of these charge-induced optical features do not match th ose observed following chemical doping. The optical characteristics of the pure C60 and the C70/C60 MIS devices are consistent with the impe dance analysis.