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

Dhara, Soumen, Niang, Kham M., Flewitt, Andrew J., Nathan, Arokia and Lynch, Stephen A. 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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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: 03 Nov 2021 14:09

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