Low-frequency current fluctuations are investigated over a bias range covering { \em ohmic}, { \em trap-filling} and { \em space-charge-limited current} regimes in polycrystalline polyacenes. The relative current noise power spectral density ${ \cal S}(f)$ is constant in the { \em ohmic} region, steeply increases at the { \em trap-filling transition} region and decreases in the { \em space-charge-limited-current} region. The { \em noise peak} at the { \em trap-filling transition} is accounted for within a { \em continuum percolation model}. As the quasi-Fermi level crosses the trap level, intricate insulating paths nucleate within the ohmic matrix, determining the onset of non-equilibrium conditions at the interface between the insulating and conducting phase. The { \em noise peak} is written in terms of the free and trapped charge carrier densities.
Categories: cond-mat.dis-nn cond-mat.mtrl-sci