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

Techniques are reported for sputter deposition of biaxially oriented buffer-layers on textured Ni tapes. These buffered tapes can be employed as long, flexible, or large area substrates for biaxially-aligned high-temperature superconductors (HTS) with high critical current density Jc. Using deposition techniques at temperatures as low as 25°C, epitaxial Pd or Pt films were first deposited as a base layer on the textured Ni tapes, followed by deposition of biaxially oriented Ag or CeO2 buffer layers. Using Ar/4%H2 sputter gas, biaxially oriented CeO2 films were also grown directly on the textured Ni tapes, followed by the epitaxial growth of YSZ films. All the films show both strong in-plane and out-of-plane orientations. The effects of Ni surface smoothness on buffer-layer texture were also investigated.

Deposition of biaxially-oriented metal and oxide buffer-layer films on textured Ni tapes: New substrates for high-current, high-temperature superconductors

Recent results on achieving ferromagnetism in transition-metal-doped GaN, A1N and related materials are discussed. The field of semiconductor spintronics seeks to exploit the spin of charge carrier ...

/pdf/wide-bandgap-gan-based-semiconductors-for-spintronics-1v1ssf8w51.pdf

Wide bandgap GaN-based semiconductors for spintronics

Strategic Learning and the Balanced Scorecard

High-performance amorphous (α−) InGaZnO-based thin film transistors (TFTs) were fabricated on flexible polyethylene terephthalate substrates coated with indium oxide (In2O3) films. The InGaZnO films were deposited by rf magnetron sputtering with the presence of O2 at room temperature. The n-type carrier concentration of InGaZnO film was ∼2×1017 cm−3. The bottom-gate-type TFTs with SiO2 or SiNx gate dielectric operated in enhancement mode with good electrical characteristics: saturation mobility 11.5 cm2 V−1 s−1 for SiO2 and 12.1 cm2 V−1 s−1 for SiNx gate dielectrics and drain current on-to-off ratio >105. TFTs with SiNx gate dielectric exhibited better performance than those with SiO2. This is attributed to the relatively high dielectric constant (i.e., high-k material) of SiNx. After more than 500 h aging time at room temperature, the saturation mobility of the TFTs with SiO2 gate dielectric was comparable to the as-fabricated value and the threshold voltage shift was 150 mV.

High performance indium gallium zinc oxide thin film transistors fabricated on polyethylene terephthalate substrates

ZnO nanowires grown by site-selected molecular beam epitaxy (MBE) were contacted at both ends by Al/Pt/Au ohmic electrodes. The current–voltage (I–V) and photoresponse characteristics were obtained both in the dark and with ultraviolet (UV, 254 or 366 nm) illumination. The I–V characteristics are ohmic under all conditions, with nanowire conductivity under UV exposure of 0.2 Ω cm. The photoresponse showed only a minor component with long decay times (tens of seconds) thought to originate from surface states. The results show the high quality of material prepared by MBE and the promise of using ZnO nanowire structures for solar-blind UV detection.

David P. Norton

Papers

Deposition of biaxially-oriented metal and oxide buffer-layer films on textured Ni tapes: New substrates for high-current, high-temperature superconductors

Wide bandgap GaN-based semiconductors for spintronics

Strategic Learning and the Balanced Scorecard

High performance indium gallium zinc oxide thin film transistors fabricated on polyethylene terephthalate substrates

UV photoresponse of single ZnO nanowires