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Posted: Mar 05, 2012

Transparent oxide-photosensor for contact-free interactive displays

(Nanowerk News) The oxide semiconductor transistor is a promising candidate for the next generation of display screens because of its high performance and high transparency associated with its wide band-gap. These properties make the transistor suitable for a range of exciting transparent display applications, e.g. new smart window technology in cars and homes.
Interestingly, although it is transparent, the oxide semiconductor can also detect visible light due to the presence of oxygen vacancies in the sub-gap states, suggesting possible transparent photosensors for visible light applications. These properties allow an oxide-photosensor integrated with a transparent display to be created, however, ionized oxygen vacancies under illumination can also lead to persistent photoconductivity (PPC). PPC causes the semiconductor material to remain conductive for hours/days, leading to low frame rates, the rate at which an imaging device produces unique consecutive images.
sensor pixel incorporating an inverted staggered switch-transistor and photo-transistor photosensor pixel array
Left: Schematic of a sensor pixel incorporating an inverted staggered switch-transistor and photo-transistor. Right: Photograph of the fully fabricated photosensor pixel array. The inset shows a photosensor composed of one photo-transistor and one switch-transistor.
LCN researcher, Sungsik Lee in collaboration with Prof. Arokia Nathan, University of Cambridge, and Samsung Advanced Institute of Technology (SAIT) showed in a recent study (see paper in Nature Materials: "Gated three-terminal device architecture to eliminate persistent photoconductivity in oxide semiconductor photosensor arrays") that a transparent active-matrix photosensor array, that can operate at high frame rates and which has potential applications in contact-free interactive displays as shown in the figure above (right), had been integrated.
The study also found that persistent photoconductivity (PPC) can be eliminated by a short-duration voltage pulse to these devices, inducing electron accumulation and accelerating their recombination with ionized oxygen vacancy sites.
Source: London Centre for Nanotechnology
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