Current voltage characteristics and excess noise at the trap filling transition in polyacenes

TL;DR

This paper investigates the trap filling transition in polyacenes, revealing a super-quadratic I-V increase and a peak in excess noise, explained by field-assisted trapping-detrapping processes, with a model matching experimental data.

Contribution

It introduces a physical model linking trap filling and excess noise in organic semiconductors, validated by experimental data in tetracene and pentacene films.

Findings

Super-quadratic I-V behavior observed at trap filling transition.

Sharp peak in excess noise correlates with I-V transition.

Model predictions agree with experimental results across various film lengths.

Abstract

Experiments in organic semiconductors (polyacenes) evidence a strong super quadratic increase of the current-voltage (I-V) characteristic at voltages in the transition region between linear (Ohmic) and quadratic (trap free space-charge-limited-current) behaviours. Similarly, excess noise measurements at a given frequency and increasing voltages evidence a sharp peak of the relative spectral density of the current noise in concomitance with the strong super-quadratic I-V characteristics. Here we discuss the physical interpretation of these experiments in terms of an essential contribution from field assisted trapping-detrapping processes of injected carriers. To this purpose, the fraction of filled traps determined by the I-V characteristics is used to evaluate the excess noise in the trap filled transition (TFT) regime. We have found an excellent agreement between the predictions of our model and existing experimental results in tetracene and pentacene thin films of different length in the range $0.65 \div 35 \ \mu m$.