비만아 부모의 돌봄 경험: q 방법론

Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

A review of Ga2O3 materials, processing, and devices

Transparent conductors as solar energy materials: A panoramic review

Beams of electrons and ions are now fairly routinely focused to dimensions in the nanometer range. Since the beams can be used to locally alter material at the point where they are incident on a surface, they represent direct nanofabrication tools. The authors will focus here on direct fabrication rather than lithography, which is indirect in that it uses the intermediary of resist. In the case of both ions and electrons, material addition or removal can be achieved using precursor gases. In addition ions can also alter material by sputtering (milling), by damage, or by implantation. Many material removal and deposition processes employing precursor gases have been developed for numerous practical applications, such as mask repair, circuit restructuring and repair, and sample sectioning. The authors will also discuss structures that are made for research purposes or for demonstration of the processing capabilities. In many cases the minimum dimensions at which these processes can be realized are considerably larger than the beam diameters. The atomic level mechanisms responsible for the precursor gas activation have not been studied in detail in many cases. The authors will review the state of the art and level of understanding of direct ion and electron beam fabrication and point out some of the unsolved problems.

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Gas-assisted focused electron beam and ion beam processing and fabrication

A common misconception is that the irradiation of solids with energetic electrons and ions has exclusively detrimental effects on the properties of target materials. In addition to the well-known cases of doping of bulk semiconductors and ion beam nitriding of steels, recent experiments show that irradiation can also have beneficial effects on nanostructured systems. Electron or ion beams may serve as tools to synthesize nanoclusters and nanowires, change their morphology in a controllable manner, and tailor their mechanical, electronic, and even magnetic properties. Harnessing irradiation as a tool for modifying material properties at the nanoscale requires having the full microscopic picture of defect production and annealing in nanotargets. In this article, we review recent progress in the understanding of effects of irradiation on various zero-dimensional and one-dimensional nanoscale systems, such as semiconductor and metal nanoclusters and nanowires, nanotubes, and fullerenes. We also consider the t...

Ion and electron irradiation-induced effects in nanostructured materials

Transparent conductive Sn-doped β-Ga2O3 single crystal with high crystallinity was successfully fabricated as a substrate for the growth of GaN-based compounds. Sn-doped β-Ga2O3 single crystals were grown using a floating zone (FZ) method, and the properties of electrical conductivity, optical transmittance, and crystallinity were characterized to optimize the growth condition. It was found that these properties are controlled by the Sn doping concentration, and the specimen for 32 ppm Sn-doped β-Ga2O3 single crystal was optimized to satisfy these properties simultaneously, i.e. the substrate with the internal optical transmittance of above ∼85% in the visible region, the electrical resistivity of 4.27×10–2 Ωcm, the carrier density of 2.26×1018 cm–3, and the FWHM of X-ray rocking curve of 43 arcsec was obtained. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication and characterization of transparent conductive Sn-doped β-Ga2O3 single crystal

Nondestructive determination of the polarity of GaN has been achieved by the use of coaxial impact-collision ion scattering spectroscopy analysis. The polarity of a GaN film with a smooth surface on non-nitrided c-plane sapphire was identified (0001) (Ga face; +c). GaN films with a 20 nm buffer layer on nitrided sapphire had (0001) (N face; −c) polarity and a hexagonal faceted surface. The influence of both the buffer layer and of substrate nitridation on the polarity of wurtzite {0001} GaN films deposited by two-step metal organic chemical vapor deposition (MOCVD) has been investigated. The polarity of the buffer layer on a nitrided sapphire substrate was altered by varying its thickness or the annealing time. It was found that the polarity of the GaN film is determined by the polarity of the annealed buffer layer; MOCVD-GaN films on buffer layers with +c and −c polarity have either +c (smooth surface) or −c (hexagonal facet) polarity, respectively.

Analysis of the polar direction of GaN film growth by coaxial impact collision ion scattering spectroscopy

Amorphous SiO2 transforms into crystalline Si by 200 kV electron irradiation at ambient temperature. The transformation of amorphous SiO2 to crystalline Si takes place in two steps; the first step involves transformation of amorphous SiO2 into amorphous Si, while the second step is the crystallization of amorphous Si. Valence electron ionization is determined as the key factor for the transformation from SiO2 to amorphous Si; beam heating and knock-on displacement are responsible for the transformation from amorphous Si to crystalline Si. The energy threshold for the crystallization of amorphous Si is determined to be 150.2 kV.

Formation of crystalline Si nanodots in SiO2 films by electron irradiation

We have successfully fabricated nano-dots containing W from a metal–organic gas source by electron-beam-induced deposition in an ultra-high vacuum transmission electron microscope. The size of the dots can be controlled by changing the time for irradiation and the partial pressure of the precursor. The smallest particle size is less than 2 nm in diameter, which is the record smallest ever made by this method.

The size dependence of the nano-dots formed by electron-beam-induced deposition on the partial pressure of the precursor

We have successfully fabricated nano-dots containing tungsten or gold from metal-organic gas sources by electron beam-induced deposition in an ultrahigh vacuum transmission electron microscope The size of the dots can be controlled by changing the time for irradiation and the partial pressure of the precursor The smallest particle size fabricated from W(CO)6 is ∼15 nm in diameter, which is close to the theoretical resolution limit Copyright © 2005 John Wiley & Sons, Ltd

Miyoko Tanaka

Papers

Fabrication and characterization of transparent conductive Sn-doped β-Ga2O3 single crystal

Analysis of the polar direction of GaN film growth by coaxial impact collision ion scattering spectroscopy

Formation of crystalline Si nanodots in SiO2 films by electron irradiation

The size dependence of the nano-dots formed by electron-beam-induced deposition on the partial pressure of the precursor

Ultimate sized nano‐dots formed by electron beam‐induced deposition using an ultrahigh vacuum transmission electron microscope