The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

/pdf/a-comprehensive-review-of-zno-materials-and-devices-21a3zjadem.pdf

A comprehensive review of zno materials and devices

ZnO nanowire (NW) visible-blind UV photodetectors with internal photoconductive gain as high as G ∼ 108 have been fabricated and characterized. The photoconduction mechanism in these devices has been elucidated by means of time-resolved measurements spanning a wide temporal domain, from 10-9 to 102 s, revealing the coexistence of fast (τ ∼ 20 ns) and slow (τ ∼ 10 s) components of the carrier relaxation dynamics. The extremely high photoconductive gain is attributed to the presence of oxygen-related hole-trap states at the NW surface, which prevents charge-carrier recombination and prolongs the photocarrier lifetime, as evidenced by the sensitivity of the photocurrrent to ambient conditions. Surprisingly, this mechanism appears to be effective even at the shortest time scale investigated of t < 1 ns. Despite the slow relaxation time, the extremely high internal gain of ZnO NW photodetectors results in gain-bandwidth products (GB) higher than ∼10 GHz. The high gain and low power consumption of NW photodetec...

http://www1.spms.ntu.edu.sg/~oson/publications/papers/NL%207,%201003%20(2007).pdf

ZnO Nanowire UV Photodetectors with High Internal Gain

https://chemistry.beloit.edu/classes/nanotech/ZnO/mattoday10_05_40.pdf

ZnO - nanostructures, defects, and devices

One-dimensional (1D) ZnO nanostructures have been studied intensively and extensively over the last decade not only for their remarkable chemical and physical properties, but also for their current and future diverse technological applications. This article gives a comprehensive overview of the progress that has been made within the context of 1D ZnO nanostructures synthesized via wet chemical methods. We will cover the synthetic methodologies and corresponding growth mechanisms, different structures, doping and alloying, position-controlled growth on substrates, and finally, their functional properties as catalysts, hydrophobic surfaces, sensors, and in nanoelectronic, optical, optoelectronic, and energy harvesting devices.

/pdf/one-dimensional-zno-nanostructures-solution-growth-and-30xs4d6be7.pdf

One-dimensional ZnO nanostructures: Solution growth and functional properties

Unlike silver and gold, aluminum has material properties that enable strong plasmon resonances spanning much of the visible region of the spectrum and into the ultraviolet. This extended response, combined with its natural abundance, low cost, and amenability to manufacturing processes, makes aluminum a highly promising material for commercial applications. Fabricating Al-based nanostructures whose optical properties correspond with theoretical predictions, however, can be a challenge. In this work, the Al plasmon resonance is observed to be remarkably sensitive to the presence of oxide within the metal. For Al nanodisks, we observe that the energy of the plasmon resonance is determined by, and serves as an optical reporter of, the percentage of oxide present within the Al. This understanding paves the way toward the use of aluminum as a low-cost plasmonic material with properties and potential applications similar to those of the coinage metals.

/pdf/aluminum-for-plasmonics-oy8t9f6wgd.pdf

Aluminum for Plasmonics

We report room-temperature, white-color electroluminescence in vertically oriented ZnO nanowires. Excitonic luminescence around 380 nm is observed as a shoulder on a broader defect-related band covering all of the visible range and centered at 620 nm. The ZnO nanowires are grown in a low-temperature process on SnO2-coated glass substrates, employing a technique that is suitable for large-area applications. The nanowires are robustly encapsulated in a thin polystyrene film deposited from high-molecular-weight solutions. Electron injection occurs through the transparent SnO2 layer, while hole injection is mediated by a p-doped polymer and an evaporated Au contact. Stable device operation is observed at ambient conditions on the time scale of 1 h.

/pdf/vertical-nanowire-light-emitting-diode-1xnqfqabm9.pdf

Vertical nanowire light-emitting diode

We report ultraviolet electroluminescence at 390 nm from diode structures consisting of electrodeposited ZnO nanorods sandwiched between a transparent SnO2 film and a p-type conducting polymer. The nanorods are embedded in an insulating polystyrene layer. ZnO deposition occurs at 90 °C and produces vertically oriented nanorods with very high uniformity over areas of ∼20 cm2. Electron diffraction shows the nanorods to be single crystalline wurtzite ZnO. As-grown films show a broad electroluminescence band over the visible spectrum. Annealing at moderate temperatures (T = 300 °C) increases the emission and strongly raises the excitonic contribution. Optimally processed films show a narrow ultraviolet electroluminescence line at ∼390 nm.

Ultraviolet electroluminescence from ZnO/polymer heterojunction light-emitting diodes.

We report a highly flexible light-emitting device in which inorganic nanowires are the optically active components. The single-crystalline ZnO nanowires are grown at 80 °C on flexible polymer-based indium-tin-oxide-coated substrates and subsequently encapsulated in a minimal-thickness, void-filling polystyrene film. A reflective top contact serving as the anode in the diode structure is provided by a strongly doped p-type polymer and an evaporated Au film. The emission through the polymer side of this arrangement covers most of the visual region. Electrical and optical properties as well as performance limitations of the device structure are discussed.

Flexible inorganic nanowire light-emitting diode.

5.4 nm spatial resolution in biological photoemission electron microscopy.

We report visible electroluminescence at room temperature in nanoporous TiO2 films using solid-state heterojunction contacts. Electrons are injected from an n-type polymer layer, while hole injection occurs from a conductive SnO2 substrate. As the polymer material penetrates into the TiO2 nanopore structure a highly non-planar interface with a greatly enlarged area is created. This type of interface establishes very short current paths to the recombination region of the device and allows high carrier fluxes from the electron-injecting contact. The electroluminescence onset occurs at 7 V applied bias, and involves a broad emission band covering most of the visible region with a peak centred at 600 nm.

https://iopscience.iop.org/article/10.1088/0957-4484/17/8/008/pdf

Robert Campbell Word

Papers

Vertical nanowire light-emitting diode

Ultraviolet electroluminescence from ZnO/polymer heterojunction light-emitting diodes.

Flexible inorganic nanowire light-emitting diode.

5.4 nm spatial resolution in biological photoemission electron microscopy.

Electroluminescence in nanoporous TiO2 solid-state heterojunctions