The composition of amorphous oxide semiconductors, which are well known for their optical transparency, can be tailored to enhance their absorption and induce photoconductivity for irradiation with green, and shorter wavelength light. In principle, amorphous oxide semiconductor-based thin-film photoconductors could hence be applied as photosensors. However, their photoconductivity persists for hours after illumination has been removed, which severely degrades the response time and the frame rate of oxide-based sensor arrays. We have solved the problem of persistent photoconductivity (PPC) by developing a gated amorphous oxide semiconductor photo thin-film transistor (photo-TFT) that can provide direct control over the position of the Fermi level in the active layer. Applying a short-duration (10 ns) voltage pulse to these devices induces electron accumulation and accelerates their recombination with ionized oxygen vacancy sites, which are thought to cause PPC. We have integrated these photo-TFTs in a transparent active-matrix photosensor array that can be operated at high frame rates and that has potential applications in contact-free interactive displays.

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Gated three-terminal device architecture to eliminate persistent photoconductivity in oxide semiconductor photosensor arrays

With large surface-to-volume ratios and Debye length comparable to their small sizes, one-dimensional inorganic nanostructures have extensively been investigated and widely used to fabricate high-performance nanoscale electronic and optoelectronic devices. This feature article reviews the state-of-the-art research activities that focus on the one-dimensional inorganic nanostructures and their photodetector applications. It begins with a survey of one-dimensional inorganic nanostructures and the fundamentals of photodetectors. Some remarkable photoresponse characteristics are then presented, which are organized into sections covering several kinds of important nanostructures, such as ZnO, V 2 O 5 , ZnS, In 2 Se 3 , InSe, CdS, CdSe, ZnSe, Sb 2 Se 3 , ZrS 2 , Ag 2 S, and Zn x Cd 1-x Se. Each section describes the corresponding photodetective properties in detail. Finally, the article concludes with some perspectives and outlook on the future developments in the field.

Recent Developments in One-Dimensional Inorganic Nanostructures for Photodetectors

With large surface-to-volume ratios and Debye length comparable to their small sizes, one-dimensional inorganic nanostructures have extensively been investigated and widely used to fabricate high-performance nanoscale electronic and optoelectronic devices This feature article reviews the state-of-the-art research activities that focus on the one-dimensional inorganic nanostructures and their photodetector applications It begins with a survey of one-dimensional inorganic nanostructures and the fundamentals of photodetectors Some remarkable photoresponse characteristics are then presented, which are organized into sections covering several kinds of important nanostructures, such as ZnO, V 2 O 5 , ZnS, In 2 Se 3 , InSe, CdS, CdSe, ZnSe, Sb 2 Se 3 , ZrS 2 , Ag 2 S, and Zn x Cd 1-x Se Each section describes the corresponding photodetective properties in detail Finally, the article concludes with some perspectives and outlook on the future developments in the field

A new Schottky junction ultraviolet photodetector (UVPD) is fabricated by coating a free-standing ZnO nanorod (ZnONR) array with a layer of transparent monolayer graphene (MLG) fi lm. The single-crystalline [0001]-oriented ZnONR array has a length of about 8‐11 μ m, and a diameter of 100 ∼ 600 nm. Finite element method (FEM) simulation results show that this novel nanostructure array/MLG heterojunction can trap UV photons effectively within the ZnONRs. By studying the I‐V characteristics in the temperature range of 80‐300 K, the barrier heights of the MLG fi lm/ZnONR array Schottky barrier are estimated at different temperatures. Interestingly, the heterojunction diode with typical rectifying characteristics exhibits a high sensitivity to UV light illumination and a quick response of millisecond rise time/fall times with excellent reproducibility, whereas it is weakly sensitive to visible light irradiation. It is also observed that this UV photodetector (PD) is capable of monitoring a fast switching light with a frequency as high as 2250 Hz. The generality of the above results suggest that this MLG fi lm/ZnONR array Schottky junction UVPD will have potential application in future optoelectronic devices.

Monolayer Graphene Film on ZnO Nanorod Array for High‐Performance Schottky Junction Ultraviolet Photodetectors

Visible-light driven photocatalyst, Ag/ZnO flower (ZnO Fl) heterostructures, was prepared on indium doped tin oxide (ITO) glass via a simple photoreduction method without surfactants. The samples are characterized by X-ray diffraction, scan electron microscopy, X-ray photoelectron spectroscopy, UV–vis spectroscopy, photoluminescence spectra and photocurrent response. The results show that ZnO FRs are wurtzite phase with single crystalline grown along the [0 0 1] direction and Ag nanoparticles (NPs) located on the surface are metallic. The binding energy of Ag 3d for the Ag/ZnO Fls sample shifts remarkably to the lower binding energy compared with the corresponding value of pure metallic Ag attribute to the interaction between Ag and ZnO Fls. Ag/ZnO Fl heterostructures exhibit higher visible-light driven photocatalytic activity. It is suggested that photo-induced electrons are generated from Ag due to surface plasmon resonance, and transfer from Ag to ZnO Fls. Then the electrons interact with adsorbed oxygen, finally forming hydroxyl radicals ( OH), and the visible-light driven photocatalytic efficiency is enhanced. The proposed mechanism is further confirmed by the photoluminescence and transient photocurrent response. Additionally, the as-prepared Ag/ZnO Fls/ITO as a convenient photocatalytic device can be recycled without centrifugation.

Ag/ZnO flower heterostructures as a visible-light driven photocatalyst via surface plasmon resonance

This study fabricates and characterizes ultraviolet (UV) photosensors with ZnO nanorods (NRs). The NR arrays were selectively grown in the gap between interdigitated (IDT) electrodes of devices using hydrothermal solution processes and a lithography-based technique. Compared with a conventional ZnO photosensor without NRs, the proposed UV NR photosensors have much higher photoresponse in the UV region. Additionally, the photoconductive gain of an NR photosensor increased as UV illumination time increased; it varied at 34.45−5.32 × 102 under illumination by 18.28 mW/cm2 optical power. Consequently, the substantial photoconductive gain can be attributed to high surface-to-volume ratio of ZnO NRs. The high density of hole-trap states on NR surfaces lead to a persistent photoconductivity (PPC) state, promoting the transport of carriers through devices.

C. Z. Wu

Papers

Ultraviolet ZnO Nanorod Photosensors