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. ...

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A comprehensive review of zno materials and devices

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

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Spintronics: Fundamentals and applications

Organizational Citizenship Behaviors: A Critical Review of the Theoretical and Empirical Literature and Suggestions for Future Research

We test the relationship between shareholder value, stakeholder management, and social issue participation. Building better relations with primary stakeholders like employees, customers, suppliers, and communities could lead to increased shareholder wealth by helping firms develop intangible, valuable assets which can be sources of competitive advantage. On the other hand, using corporate resources for social issues not related to primary stakeholders may not create value for shareholders. We test these propositions with data from S&P 500 firms and find evidence that stakeholder management leads to improved shareholder value, while social issue participation is negatively associated with shareholder value. Copyright © 2001 John Wiley & Sons, Ltd.

http://faculty.wwu.edu/dunnc3/rprnts.shareholdervaluesocialissues.pdf

Shareholder value, stakeholder management, and social issues: what's the bottom line?

In the past ten years we have witnessed a revival of, and subsequent rapid expansion in, the research on zinc oxide (ZnO) as a semiconductor. Being initially considered as a substrate for GaN and related alloys, the availability of high-quality large bulk single crystals, the strong luminescence demonstrated in optically pumped lasers and the prospects of gaining control over its electrical conductivity have led a large number of groups to turn their research for electronic and photonic devices to ZnO in its own right. The high electron mobility, high thermal conductivity, wide and direct band gap and large exciton binding energy make ZnO suitable for a wide range of devices, including transparent thin-film transistors, photodetectors, light-emitting diodes and laser diodes that operate in the blue and ultraviolet region of the spectrum. In spite of the recent rapid developments, controlling the electrical conductivity of ZnO has remained a major challenge. While a number of research groups have reported achieving p-type ZnO, there are still problems concerning the reproducibility of the results and the stability of the p-type conductivity. Even the cause of the commonly observed unintentional n-type conductivity in as-grown ZnO is still under debate. One approach to address these issues consists of growing high-quality single crystalline bulk and thin films in which the concentrations of impurities and intrinsic defects are controlled. In this review we discuss the status of ZnO as a semiconductor. We first discuss the growth of bulk and epitaxial films, growth conditions and their influence on the incorporation of native defects and impurities. We then present the theory of doping and native defects in ZnO based on density-functional calculations, discussing the stability and electronic structure of native point defects and impurities and their influence on the electrical conductivity and optical properties of ZnO. We pay special attention to the possible causes of the unintentional n-type conductivity, emphasize the role of impurities, critically review the current status of p-type doping and address possible routes to controlling the electrical conductivity in ZnO. Finally, we discuss band-gap engineering using MgZnO and CdZnO alloys.

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Fundamentals of zinc oxide as a semiconductor

Strong, Asymmetric Flux Pinning by Miscut-Growth-Initiated Columnar Defects in Epitaxial YBa[subscript 2]Cu[subscript 3]O[subscript 7—chi] Films

In continuation of our effort to develop single buffer layer architectures for YBCO (YBa 2 Cu 3 O 7- g ) coated tape conductors, we have studied RE 2 O 3 (RE = Y, and rare earths) as candidate materials. Three types of crystal structures including the preferred cubic phase are known for the rare earth oxides. High quality simple cubic RE 2 O 3 buffer layers were grown epitaxiahy on {100} textured Ni substrates using both reactive evaporation and sol-gel processing. Detailed X-ray studies have shown that the Y 2 O 3 , Eu 2 O 3 , Gd 2 O 3 , and Yb 2 O 3 were grown with a single epitaxial orientation. SEM micrographs indicated that both e-beam and sol-gel grown films were dense, continuous and crack free. High J c YBCO films were grown on RE 2 O 3 -buffered Ni substrates with sputtered cap layers. Two new alternative buffer layer architectures were developed. A high J c of 1.8 MA/cm 2 at 77 K and self-field was obtained on YBCO films with a layer sequence of YBCO (pulsed laser deposition)/Yb 2 O 3 (sputtered)/Y 2 O 3 (e-beam)/Ni. Also, a high J c of over 1 MA/cm 2 at 77 K and self-field was obtained on YBCO films with a layer sequence of YBCO (ex-situ BaF 2 process)/CeO 2 (sputtered)YSZ sputtered)/RE 2 O 3 (sol-gel or e-beam)Ni. The performance of sol-gel grown buffers approached the quality of e-beam grown buffers.

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Demonstration of High Current Density YBCO Coated Conductors on RE 2 O 3 -Buffered Ni Substrates with Two New Alternative Architectures

Pulsed-laser deposition has been utilized to grow metastable and artificially-layered copper oxide thin-film materials. Single-crystal thin films of Ca 1 − x Sr x CuO 2 , the ‘infinite layer’ parent compound for the high temperature superconductors, have been grown over the composition range 0.15 ≤ x ≤ 1.0 utilizing a single-target co-deposition growth scheme. These Ca 1 − x Sr x CuO 2 thin films are very high-quality single crystals of the tetragonal, infinite layer phase with extremely narrow diffraction peaks, complete in-plane crystalline alignment with the (100) SrTiO 3 substrate, and virtually no impurity phases present. In addition, superlattice structures, consisting of SrCuO 2 and (Sr,Ca)CuO 2 layers in the tetragonal, ‘infinite layer’ crystal structure, have been grown by pulsed-laser deposition. These results greatly enhance the possibility of developing new, artificially-layered high temperature superconducting phases via pulsed-laser deposition.

Artificially-layered and metastable thin-film materials development utilizing pulsed-laser deposition

Pulsed-laser deposition and epitaxial stabilization have been effectively used to engineer artificially-layered thin- film materials. Novel cuprate compounds have been synthesized using the constraint of epitaxy to stabilize (Ca,Sr)CuO2/(Ba,Ca,Sr)CuO2 superconducting superlattices in the infinite layer structure. Superlattice chemical modulation can be observed from the x-ray diffraction patterns for structures with SrCuO2 and (Ca,Sr)CuO2 layers as thin as a single unit cell. X-ray diffraction intensity oscillations, due to the infinite thickness of the film, indicate that (Ca,Sr)CuO2 films grown by pulsed-laser deposition are extremely flat with a thickness variation of only approximately 20 angstrom over a length scale of several thousand angstroms. This enables the unit-cell control of (Ca,Sr)CuO2 film growth in an oxygen pressure regime in which in situ surface analysis using electron diffraction is not possible. With the incorporation of BaCuO2 layers, superlattice structures have been synthesized which superconduct at temperatures as high as 70 K. Dc transport measurements indicate that (Ca,Sr)CuO2/BaCuO2 superlattices are two dimensional superconductors with the superconducting transition primarily associated with the BaCuO2 layers. Superconductivity is observed only for structures with BaCuO2 layers at least two unit cells thick with Tc decreasing as the (Ca,Sr)CuO2 layer thickness increases. Normalized resistance in the superconducting region collapse to the Ginzburg-Landau Coulomb gas universal resistance curve consistent with the two-dimensional vortex fluctuation model.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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Formation and properties of novel artificially layered cuprate superconductors using pulsed-laser deposition

ZnO nanorods with typical lengths and diameters of /spl sim/2 /spl mu/m and 15-30 nm, respectively, were grown on Ag-coated Si substrate by catalyst-driven Molecular Beam Epitaxy and subsequently implanted with Mn/sup +/ or Co/sup +/ ions of dose ranging from 1-5/spl times/10/sup 16/ cm/sup -2/. The samples were then annealed at 700/spl deg/C for 5 minutes. The structural properties were unaffected, but they exhibited ferromagnetism that persisted up to temperatures of 225-300 K. Coersive fields were /spl les/100 Oe even at 10 K. The results are similar to those obtained for implantation of Mn/sup +/ and Co/sup +/ ions in bulk, single-crystal ZnO, indicating the promise of nanorods for nanoscale spintronics.

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David P. Norton

Papers

Strong, Asymmetric Flux Pinning by Miscut-Growth-Initiated Columnar Defects in Epitaxial YBa[subscript 2]Cu[subscript 3]O[subscript 7—chi] Films

Demonstration of High Current Density YBCO Coated Conductors on RE 2 O 3 -Buffered Ni Substrates with Two New Alternative Architectures

Artificially-layered and metastable thin-film materials development utilizing pulsed-laser deposition

Formation and properties of novel artificially layered cuprate superconductors using pulsed-laser deposition

Ferromagnetism in Mn- and Co-implanted ZnO nanorods