EFFECTS OF OXYGEN ON THE PHOTOCARRIER DYNAMICS IN A C60 FILM - STUDIES OF TRANSIENT AND STEADY-STATE PHOTOCONDUCTIVITY

The intrinsic dynamics of photoexcited carriers in an oxygen-free C60 film and their remarkable evolution as the film is exposed to oxygen a re revealed by transient and steady-state photoconductivity (PC) measu rements at various temperatures, light intensities, and photon energie s. Exposure of C60 film to oxygen creates deep traps that reduce drast ically the carrier lifetime and, consequently, the room-temperature st eady-state photoconductivity by three to six orders of magnitude. Oxyg en affects the steady-state photoconductivity excitation spectrum in a qualitatively similar way, as does decreasing the ambient temperature ; in both cases, the photoconductivity decreases faster when carriers are photoexcited into the band edges. The transient and steady-state P C of a C60 film fully exposed to oxygen becomes temperature independen t.