Optical generation of hot electrons in metallic structures and its potential as an alternative to conventional electron–hole separation in semiconductor devices are reviewed. The possibilities for realizing high conversion efficiencies with low fabrication costs are discussed along with challenges in terms of the materials, architectures and fabrication methods

Plasmon-induced hot-electron generation at nanoparticle/metal-oxide interfaces for photovoltaic and photocatalytic devices

The present status and prospects for further development of polycrystalline or amorphous transparent conducting oxide (TCO) semiconductors used for practical thin-film transparent electrode applications are presented in this paper. The important TCO semiconductors are impurity-doped ZnO, In2O3 and SnO2 as well as multicomponent oxides consisting of combinations of ZnO, In2O3 and SnO2, including some ternary compounds existing in their systems. Development of these and other TCO semiconductors is important because the expanding need for transparent electrodes for optoelectronic device applications is jeopardizing the availability of indium-tin-oxide (ITO), whose main constituent, indium, is a very expensive and scarce material. Al- and Ga-doped ZnO (AZO and GZO) semiconductors are promising as alternatives to ITO for thin-film transparent electrode applications. In particular, AZO thin films, with a low resistivity of the order of 10−5 Ω cm and source materials that are inexpensive and non-toxic, are the best candidates. However, further development of the deposition techniques, such as magnetron sputtering or vacuum arc plasma evaporation, as well as of the targets is required to enable the preparation of AZO and GZO films on large area substrates with a high deposition rate.

https://iopscience.iop.org/article/10.1088/0268-1242/20/4/004/pdf

Transparent conducting oxide semiconductors for transparent electrodes

Materials research plays a vital role in transforming breakthrough scientific ideas into next-generation technology. Similar to the way silicon revolutionized the microelectronics industry, the proper materials can greatly impact the field of plasmonics and metamaterials. Currently, research in plasmonics and metamaterials lacks good material building blocks in order to realize useful devices. Such devices suffer from many drawbacks arising from the undesirable properties of their material building blocks, especially metals. There are many materials, other than conventional metallic components such as gold and silver, that exhibit metallic properties and provide advantages in device performance, design flexibility, fabrication, integration, and tunability. This review explores different material classes for plasmonic and metamaterial applications, such as conventional semiconductors, transparent conducting oxides, perovskite oxides, metal nitrides, silicides, germanides, and 2D materials such as graphene. This review provides a summary of the recent developments in the search for better plasmonic materials and an outlook of further research directions.

/pdf/alternative-plasmonic-materials-beyond-gold-and-silver-1p8fd7ol50.pdf

Alternative Plasmonic Materials: Beyond Gold and Silver

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

ZnO - nanostructures, defects, and devices

Plasmonics is a research area merging the fields of optics and nanoelectronics by confining light with relatively large free-space wavelength to the nanometer scale - thereby enabling a family of novel devices. Current plasmonic devices at telecommunication and optical frequencies face significant challenges due to losses encountered in the constituent plasmonic materials. These large losses seriously limit the practicality of these metals for many novel applications. This paper provides an overview of alternative plasmonic materials along with motivation for each material choice and important aspects of fabrication. A comparative study of various materials including metals, metal alloys and heavily doped semiconductors is presented. The performance of each material is evaluated based on quality factors defined for each class of plasmonic devices. Most importantly, this paper outlines an approach for realizing optimal plasmonic material properties for specific frequencies and applications, thereby providing a reference for those searching for better plasmonic materials.

/pdf/searching-for-better-plasmonic-materials-4ch9r4cri1.pdf

Searching for better plasmonic materials

Low resistivity transparent conducting Al-doped ZnO films prepared by pulsed laser deposition

Highly conducting transparent indium tin oxide films prepared by pulsed laser deposition

In2O3 doped with 5 wt% SnO2 (indium-tin oxide(ITO)(5 wt%)) films have been deposited on glass and quartz substrates in a magnetic field generated from three pieces of rare–earth permanent magnets (1.25 T flux density) placed at every 120° angle to surround the plume produced by pulsed laser deposition using an ArF laser (λ=193 nm). In all experiments, a repetition rate of 10 Hz, an energy density of 1.5 J/cm2, and an irradiation time of 20–30 min (12000–18000 shots) were used. The lowest resistivity of 7.2×10-5 Ωcm and an optical transmittance of more than 90% in the visible region of the spectrum were obtained for approximately 30-nm-thick ITO (5 wt%) films deposited at a substrate temperature of 300°C in oxygen with a flow rate of 2 sccm. Very smooth surfaces with an average surface roughness of 0.61 nm were observed by scanning electron microscope (SEM) and atomic force microscope (AFM).

Pulsed Laser Deposition of Transparent Conducting Indium Tin Oxide Films in Magnetic Field Perpendicular to Plume

Approximately 800-nm-thick ZnO films doped with 4 wt% Ga2O3 (GZO films) have been deposited on glass and quartz substrates by a pulsed laser deposition method using Second-Harmonic-Genreation (SHG) of Nd:YAG laser (λ=532 nm). In all experiments, a repetition rate of 10 Hz, energy densities of 0.1–2.5 J/cm2, and irradiation times of 2–3 h were used. Scanning Electron Microscopy (SEM) observations of the film surface revealed that there were micro-textured structures (0.5–1 µm in diameter), surrounded by small rugged and irregular structures (250–400 nm in size). It was recognized from XRD spectra that a strong peak of (103) planes reflected from the micro-textured milky surfaces is dominant. A haze ratio of 46.6 % was obtained at a wavelength of 550 nm for approximately 800-nm-thick GZO (4 wt%) films grown at a substrate temperature of 300 °C in oxygen with a flow rate of 3 sccm. The lowest resistivity of 2.33×10-4 Ωcm and the lowest sheet resistance of 2.72 Ω/sq were obtained for these GZO (4 wt%) films.

https://iopscience.iop.org/article/10.1143/JJAP.38.L71/pdf

Micro-textured milky zno:ga thin films fabricated by pulsed laser deposition using second-harmonic-generation of nd:yag laser

The effect of Ag addition (0-100 wt%) to Bi2-xPbxSr2Ca2Cu3Oy (x=0.1-1.0) was systematically studied using differential thermal analysis (DTA), electrical resistivity, change in inductance, scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies. The sample was prepared by the optimum thermal procedure in which the sintering was done at the endothermic peak temperature judging from the DTA curve. It was found that the 110 K phase was produced with good reproducibility by the lowering of the melting temperature due to the addition of Ag. It was also found that high-Tc (end) corresponded well to the high-Tc fraction m= Sigma H/( Sigma H+ Sigma L+ Sigma l) (H: 2223, L: 2212, l: Ca2PbO4, Ca2CuO3) defined from the result of XRD measurements.

https://iopscience.iop.org/article/10.1088/0953-2048/7/4/007/pdf

Masahiro Okuda

Papers

Low resistivity transparent conducting Al-doped ZnO films prepared by pulsed laser deposition

Highly conducting transparent indium tin oxide films prepared by pulsed laser deposition

Pulsed Laser Deposition of Transparent Conducting Indium Tin Oxide Films in Magnetic Field Perpendicular to Plume

Micro-textured milky zno:ga thin films fabricated by pulsed laser deposition using second-harmonic-generation of nd:yag laser

The effect of Ag on the superconductivity of Bi2−xPbxSr2Ca2Cu3Oy superconductors prepared by an optimum thermal procedure