Tail state mediated conduction in zinc tin oxide thinfilm phototransistors under below bandgap optical excitation

Dhara, Soumen ORCID: https://orcid.org/0000-0002-4774-3966, Niang, Kham M., Flewitt, Andrew J., Nathan, Arokia and Lynch, Stephen A. ORCID: https://orcid.org/0000-0001-9818-2284 2021. Tail state mediated conduction in zinc tin oxide thinfilm phototransistors under below bandgap optical excitation. Scientific Reports 11 (1) , 19016. 10.1038/s41598-021-98339-4

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Abstract

We report on the appearance of a strong persistent photoconductivity (PPC) and conductor-like behaviour in zinc tin oxide (ZTO) thinfilm phototransistors. The active ZTO channel layer was prepared by remote plasma reactive sputtering and possesses an amorphous structure. Under sub-bandgap excitation of ZTO with UV light, the photocurrent reaches as high as ~ 10−4 A (a photo-to-dark current ratio of ~ 107) and remains close to this high value after switching off the light. During this time, the ZTO TFT exhibits strong PPC with long-lasting recovery time, which leads the appearance of the conductor-like behaviour in ZTO semiconductor. In the present case, the conductivity changes over six orders of magnitude, from ~ 10−7 to 0.92/Ω/cm. After UV exposure, the ZTO compound can potentially remain in the conducting state for up to a month. The underlying physics of the observed PPC effect is investigated by studying defects (deep states and tail states) by employing a discharge current analysis (DCA) technique. Findings from the DCA study reveal direct evidence for the involvement of sub-bandgap tail states of the ZTO in the strong PPC, while deep states contribute to mild PPC.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Additional Information:	This article is licensed under a Creative Commons Attribution 4.0 International License
Publisher:	Nature Research
ISSN:	2045-2322
Funders:	EPSRC
Date of First Compliant Deposit:	1 October 2021
Date of Acceptance:	24 August 2021
Last Modified:	12 May 2023 20:13
URI:	https://orca.cardiff.ac.uk/id/eprint/144598

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