Space-Charge-Limited Current Fluctuations in Organic Semiconductors

TL;DR

This paper studies low-frequency current fluctuations in polycrystalline polyacenes across different conduction regimes, revealing a noise peak at the trap-filling transition explained by a continuum percolation model.

Contribution

It introduces a continuum percolation model to explain the noise peak at the trap-filling transition in organic semiconductors.

Findings

Noise spectral density is constant in ohmic regime.

Noise peaks at trap-filling transition.

Model relates noise to free and trapped charge densities.

Abstract

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.