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

Superlattice structures, consisting of SrCuO2 and (Sr,Ca)CuO2 layers in the tetragonal, ‘‘infinite layer’’ crystal structure, have been grown by pulsed‐laser deposition. Superlattice chemical modulation is observed for structures with SrCuO2 and (Sr,Ca)CuO2 layers as thin as a single unit cell (∼3.4 A). X‐ray diffraction intensity oscillations, due to the finite thickness of the film, indicate that these films are extremely flat with a thickness variation of only ∼20 A over a length scale of several thousand angstroms. These results show that unit‐cell control of (Sr,Ca)CuO2 growth is possible in an oxygen pressure regime in which in situ surface analysis is not possible.

SrCuO2/(Sr,Ca)CuO2 superlattice growth by pulsed‐laser deposition

A brief review is given of recent developments in wide bandgap semiconductor nanowire synthesis and devices fabricated on these nanostructures. There is strong interest in these devices for applications in UV detection, gas sensors and transparent electronics.

GaN, ZnO and InN nanowires and devices.

Transport and structural properties of Sr 1− x CuO 2−δ thin films grown by pulsed laser deposition support the contention that the tetragonal phase is capable of accommodating a significant density of alkaline-earth deficiencies up to x ≤0.3. Resistivity measurements indicate a significant change in the carrier density of the CuO 2 planes as Sr vacancies are introduced. In addition, an enigmatic anomaly in the resistivity at 185 K is observed for Sr 0.85 CuO 2−δ thin films. Magnetic measurements on these samples indicate that, although a significant drop in resistivity at 185 K is observed, it is not due to a superconducting transition. Hall measurements, as well as changes in the resistivity with film growth conditions, suggest that the majority carriers in these Sr 1− x CuO 2−δ thin films are electrons even with the Sr-vacancies present.

Anomalous transport and structural properties of Sr1−xCuO2−δ thin films

The authors report an investigation of the effects of channel dimensions on the properties of amorphous-InGaZnO4 (a-IGZO) thin-film transistors (TFTs) that are associated with surface depletion and surface/volume ratio. As the channel width decreased below a critical value of around 100 nm, the on current abruptly decreased and the threshold voltage abruptly increased. The magnitude of hysteresis behavior also depended on the channel size. Both of these effects result from the change of channel resistance that can be explained by surface changes due to adsorption of oxygen or water vapor. The authors also investigated short channel a-IGZO TFTs and observed short channel effects below a critical value of channel length of 900 nm. The breakdown electric field of a-IGZO was found to be in the range of 0.4–0.8 MV/cm.

Effects of channel dimensions on performance of a-InGaZnO4 thin-film transistors

Zinc oxide is generally considered to be radiation hard, although there are few experimental reports supporting this assertion. In this paper, we present results on the changes in electrical performance of bulk Pt/ZnO Schottky rectifiers exposed to 40-MeV protons at fluences from 5×109 cm−2 to 5×1010 cm−2. These doses correspond to more than 10 years or 100 years, respectively, in low-earth satellite orbit. The reverse breakdown voltage of the ZnO diodes increased from ∼3.6V in unirradiated devices to ∼4 V after the highest proton dose. The effective barrier height decreased with proton dose, while the diode ideality factor increased from 1.8 to 1.9 for the highest dose. These devices appear promising for both aerospace and terrestrial applications where irradiation hardness is a prerequisite. The main degradation mechanism appears to be creation of recombination centers and traps.

David P. Norton

Papers

SrCuO2/(Sr,Ca)CuO2 superlattice growth by pulsed‐laser deposition

GaN, ZnO and InN nanowires and devices.

Anomalous transport and structural properties of Sr1−xCuO2−δ thin films

Effects of channel dimensions on performance of a-InGaZnO4 thin-film transistors

Proton irradiation of ZnO schottky diodes