Several experimental groups have reported recently an intriguing high level of gain (Photomultiplication) in vertical organic photoresistance (as well as in other technologies, such as perovskite for instance). This mechanism is sometimes named as “Trap-Assisted Photomultiplication.” This paper investigates the origin of this mechanism by means of drift diffusion simulations, analytical theory, and experiments, considering the particular case of PCDTBT:PC60BM photoresistors, although some conclusions are likely to apply in other technologies. It turns out that an excess of charges (induced by electron–hole carrier generation) may trigger additional carrier injection, leading to photomultiplication, under specific circumstances. We call this mechanism “gain by injection enhancement.” Electron (respectively, hole) trapping for P only (respectively, N only) devices can play this role efficiently. As these additional carriers came from contacts, significant dark current injection is thus needed to achieve a large value of gain, explaining why this mechanism can occur only in P (or N) only photoresistors (and not photodiodes or intrinsic photoresistors, i.e., with midgap contacts). In such devices, however, the detectivity remains intrinsically limited by the high level of dark injection currents required to get gain, and consequently, this type of device may be interesting, in particular, in technologies where it is not possible to achieve low dark currents using photodiodes. However, penalized by the slow trap dynamics, the cut-off frequency of these devices remains extremely low (<100 Hz). Also, this gain takes a high value only at low irradiance, making photoresistor responsivity light dependent. All these results bring new light in analyzing and optimizing photoresistors, opening a large field of investigation to take advantage of gain by injection enhancement.
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7 February 2020
Research Article|
February 05 2020
Physics of trap assisted photomultiplication in vertical organic photoresistors
Mehdi Daanoune;
Mehdi Daanoune
1
Institut d’Optique Graduate School, Université de Lyon, UJM-Saint-Etienne CNRS UMR 5516, Laboratoire Hubert Curien
, 42023 Saint-Etienne, France
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Raphaël Clerc
;
Raphaël Clerc
a)
1
Institut d’Optique Graduate School, Université de Lyon, UJM-Saint-Etienne CNRS UMR 5516, Laboratoire Hubert Curien
, 42023 Saint-Etienne, France
a)Author to whom correspondence should be addressed: raphael.clerc@institutoptique.fr
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Bruno Flament;
Bruno Flament
2
Univ. Bordeaux, IMS, CNRS, UMR 5218, Bordeaux INP, ENSCBP
, F-33405 Talence, France
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Lionel Hirsch
Lionel Hirsch
2
Univ. Bordeaux, IMS, CNRS, UMR 5218, Bordeaux INP, ENSCBP
, F-33405 Talence, France
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a)Author to whom correspondence should be addressed: raphael.clerc@institutoptique.fr
J. Appl. Phys. 127, 055502 (2020)
Article history
Received:
September 01 2019
Accepted:
January 23 2020
Citation
Mehdi Daanoune, Raphaël Clerc, Bruno Flament, Lionel Hirsch; Physics of trap assisted photomultiplication in vertical organic photoresistors. J. Appl. Phys. 7 February 2020; 127 (5): 055502. https://doi.org/10.1063/1.5126338
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