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

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

Objective:To revise the “Clinical Practice Guidelines for the Sustained Use of Sedatives and Analgesics in the Critically Ill Adult” published in Critical Care Medicine in 2002.Methods:The American College of Critical Care Medicine assembled a 20-person, multidisciplinary, multi-institutional task f

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Clinical Practice Guidelines for the Management of Pain, Agitation, and Delirium in Adult Patients in the Intensive Care Unit

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

ZnO - nanostructures, defects, and devices

Transparent conductors as solar energy materials: A panoramic review

We have investigated the electronic structures of n- or p-type doped ZnO based on ab initio electronic band structure calculations. We find unipolarity in ZnO; n-type doping using Al, Ga or In species decreases the Madelung energy while p-type doping using N species increases the Madelung energy, in addition to causing substantial localization of the N states. Codoping using reactive codopants, Al, Ga or In, enhances the incorporation of N acceptors in p-type codoped ZnO. We find the delocalized states of N for p-type ZnO codoped with N and Al (Ga).

https://iopscience.iop.org/article/10.1143/JJAP.38.L166/pdf

Solution Using a Codoping Method to Unipolarity for the Fabrication of p-Type ZnO

We investigate unipolarity in ZnO based on ab initio electronic band structure calculations. We find that p-type doping using Li, N or As species causes an increase in Madelung energy, n-type doping using B, Al, Ga, In or F species gives rise to a decrease in Madelung energy. In order to solve the unipolarity, to fabricate p-type ZnO, we propose a codoping method using acceptors and reactive donors simultaneously. A codopant pair including Ga-reactive donors and N-acceptors is eminently suitable for use in the codoping. For Li-acceptors, F species is a good candidate for reactive donors. For As-acceptors, Ga species is a preferable codopant.

Physics and control of valence states in ZnO by codoping method

Codoping for the fabrication of p-type ZnO

We use In species as reactive codopants for N acceptors to realize p-type ZnS. We find a change in the impurity states of N acceptors between ZnS : N and ZnS : (2N, In), based on the calculated results using ab initio electronic band structure calculations: while we find highly localized states of N acceptors for ZnS : N, we verify delocalized states for ZnS : (2N, In).

Control of valence states for ZnS by triple-codoping method

We review our new valence control method of a co-doping for the fabrication of low-resistivity p-type GaN, p-type AlN and n-type diamond. The co-doping method is proposed based upon ab initio electronic structure calculation in order to solve the uni-polarity and the compensation problems in the wide band-gap semiconductors. In the co-doping method, we dope both the acceptors and donors at the same time by forming the meta-stable acceptor-donor-acceptor complexes for the p-type or donor-acceptor-donor complexes for the n-type under thermal non-equilibrium crystal growth conditions. We propose the following co-doping method to fabricate the low-resistivity wide band-gap semiconductors; p-type GaN: [Si + 2 Mg (or Be)], [H + 2 Mg (or Be)], [O + 2 Mg (or Be)], p-type AlN: [O + 2 C] and n-type diamond: [B + 2 N], [H + S], [H + 2 P]. We compare our prediction of the co-doping method with the recent successful experiments to fabricate the low-resistivity p-type GaN, p-type AlN and n-type diamond. We show that the co-doping method is the efficient and universal doping method by which to avoid carrier compensation with an increase of the solubility of the dopant, to increase the activation rate by decreasing the ionization energy of acceptors and donors, and to increase the mobility of the carrier.

https://iopscience.iop.org/article/10.1088/0953-8984/13/40/304/pdf

Codoping method for the fabrication of low-resistivity wide band-gap semiconductors in p-type GaN, p-type AlN and n-type diamond: prediction versus experiment

Tetsuya Yamamoto

Papers

Solution Using a Codoping Method to Unipolarity for the Fabrication of p-Type ZnO

Physics and control of valence states in ZnO by codoping method

Codoping for the fabrication of p-type ZnO

Control of valence states for ZnS by triple-codoping method

Codoping method for the fabrication of low-resistivity wide band-gap semiconductors in p-type GaN, p-type AlN and n-type diamond: prediction versus experiment