TRANSIENT AND STEADY-STATE PHOTOCONDUCTIVITY OF A SOLID C-60 FILM

We report the experimental results of the subnanosecond time-resolved transient photoconductivity (PC) of solid C60 film at various photon e nergies, and the spectral response of the steady-state PC in the energ y range between 1.5 and 4.5 eV. The initial fast transient PC response decays exponentially in the subnanosecond time regime, followed by a weak slower component. Decay time at HBARomega = 2. 0 eV is longer tha n that at HBARomega = 2.6 and 2.9 eV. At HBARomega = 2.0 eV, transient PC peak shows a superlinear intensity dependence, suggesting carrier generation via exciton-exciton collision ionization, consistent with t he recent results of fast photoinduced absorption. However, the linear intensity dependence of the transient PC at HBARomega = 2.6 and 2.9 e V and a sharp increase of the transient and steady-state PC response a t HBARomega almost-equal-to 2.3 eV indicate direct photogeneration of free electrons and holes at HBARomega > 2.3 eV.