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.
Highlights
We report on the appearance of a strong persistent photoconductivity (PPC) and conductor-like behaviour in zinc tin oxide (ZTO) thinfilm phototransistors
We have previously reported the direct measurement of the density of sub-bandgap states by photothermal deflection spectroscopy (PDS) and photoconductive laser spectroscopy, which are very sensitive optical absorption methods[53,54]
We have demonstrated that sub-bandgap light excitation near the conduction band (CB) of the ZTO thinfilm phototransistors leads to strong PPC with long-lasting recovery time with an associated transition from semiconductor ZTO to conductor-like ZTO
Summary
We report on the appearance of a strong persistent photoconductivity (PPC) and conductor-like behaviour in zinc tin oxide (ZTO) thinfilm phototransistors. Under sub-bandgap excitation of ZTO with UV light, the photocurrent reaches as high as ~ 1 0−4 A (a photo-to-dark current ratio of ~ 1 07) 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. We observed strong PPC with a high value of the photo-to-dark current ratio (sensitivity) and appearance of the conductor-like behaviour in the ZTO semiconductor. A correlation between photoexcitation energy and DOS distribution is discussed in detail, leading to a direct evidence of the involvement of tail states of the ZTO in the observed strong PPC. We describe how the discharge current analysis (DCA) technique was employed to establish the density and distribution of sub-bandgap defect states near the conduction band edge. Some of the experimental techniques used for this work are further expanded upon in the Methods section
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