Impurity assisted hopping conduction and persistent photoconductivity in disordered carbon nanoparticle film

Abstract

We report the temperature-dependent electrical transport and photoconductivity in carbon nanoparticle films. The electrical transport is dominated by thermally activated conduction at higher temperatures in the range of ∼350-285 K, whereas at lower temperatures <280 K, the conduction is mostly due to the hopping mechanism. A film of an n-type semiconductor with a carrier concentration of ∼1016 cm-3 is prepared by pulsed laser ablation in the scanning technique. The photoconductivity shows a persistent behavior that lasts for several hundreds of seconds on sub-bandgap laser excitations. A broad green luminescence spectrum suggests the presence of a large number of oxygenated-impurity states in the nanoparticles. An unusual behavior in the temperature-dependent photoluminescence is observed in which the photoluminescence intensity first increases up to ∼100 K with the increasing temperature followed by a continuous decrease at higher temperatures. The observed persistent nature of the photocurrent and anomalous temperature dependence in photoluminescence is attributed to the presence of a large number of trap states in the nanoparticles. Due to the ability to trap and retain charges within the disordered carbon nanoparticle films, it can be utilized in the memory applications.