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Space-charge-limited current fluctuations in organic semiconductors
A Carbone1, B K Kotowska, D Kotowski
1Physics Department and National Institute of Matter Physics (INFM), Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Torino, Italy.
Physical Review Letters
|December 31, 2005
Summary
Low-frequency current fluctuations in polycrystalline polyacenes reveal a noise peak at the trap-filling transition. This peak, explained by percolation theory, relates to insulating path nucleation and charge carrier densities.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Organic Electronics
Background:
- Understanding charge transport mechanisms in organic semiconductors is crucial for device performance.
- Polycrystalline polyacenes exhibit complex electrical behavior influenced by grain boundaries and trap states.
Purpose of the Study:
- To investigate low-frequency current fluctuations (noise) in polycrystalline polyacenes across different electrical regimes.
- To elucidate the physical origins of noise peaks observed at the trap-filling transition.
Main Methods:
- Experimental measurement of relative current noise power spectral density (S(f)) as a function of bias.
- Theoretical modeling using a continuum percolation model.
Main Results:
- Noise power spectral density is constant in the Ohmic regime, increases sharply at the trap-filling transition, and decreases in the space-charge-limited current regime.
- A distinct noise peak is observed at the trap-filling transition.
- The noise peak is attributed to the nucleation of insulating paths within the conducting matrix.
Conclusions:
- The continuum percolation model successfully explains the noise peak at the trap-filling transition.
- Nonequilibrium conditions arise at the interface between insulating and conducting phases due to quasi-Fermi level crossing trap levels.
- The noise peak magnitude is directly related to free and trapped charge carrier densities.
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