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

Bulk nanostructured materials from severe plastic deformation

Physical metallurgy of Ti–Ni-based shape memory alloys

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

Wurtzitic ZnO is a wide-bandgap (3.437 eV at 2 K) semiconductor which has many applications, such as piezoelectric transducers, varistors, phosphors, and transparent conducting films. Most of these applications require only polycrystalline material; however, recent successes in producing large-area single crystals have opened up the possibility of producing blue and UV light emitters, and high-temperature, high-power transistors. The main advantages of ZnO as a light emitter are its large exciton binding energy (60 meV), and the existence of well-developed bulk and epitaxial growth processes; for electronic applications, its attractiveness lies in having high breakdown strength and high saturation velocity. Optical UV lasing, at both low and high temperatures, has already been demonstrated, although efficient electrical lasing must await the further development of good, p-type material. ZnO is also much more resistant to radiation damage than are other common semiconductor materials, such as Si, GaAs, CdS, and even GaN; thus, it should be useful for space applications.

Recent Advances in ZnO Materials and Devices

Growth conditions for the preparation of a single Al 64 Cu 23 Fe 13 icosahedral (1-) quasicrystal with excellent quasicrystallinity were examined using the Czochralski method. The appreciation of the quasicrystallinity of the grown single quasicrystal was performed by X-ray structural analysts. The full widths at half-maximum (FWHM) of the Bragg reflections along 2-, 3- and 5-fold symmetry directions have no Q || and Q⊥ dependence. Where the Q || and Q⊥ mean the phason momentum and real scattering vector. Furthermore, peak shifts from ideal Bragg positions were not observed. These means that the grown Al 64 Cu 23 Fe 13 quasicrystal by the Czochralski method has perfect I-phase structure.

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Growth condition and x-ray analysis of single Al64Cu23Fe13 icosahedral quasicrystal by the Czochralski method

Present work is aimed to obtain a clear idea of the phase stabilities of the title oxide at temperatures from 10K to 900K. X-ray powder and single-crystal diffraction measurements and neutron high-resolution powder diffraction measurements were carried out for the samples annealed in several different atmospheres i.e. CO+CO 2 or O 2 +Ar mixed gas, air, vacuum at about 10 −3 Pa. Clear evidence that NiO 6 octahedrons rotate in the bc-plane( b> > a setting) in La 2 NiO 4.00 at room temperature was obtained. Shape of a magnetic peak 011 shows some broadening at temperatures below 70K i.e. LTO 2 range.

Tetragonal and orthorhombic phases of La2NiO4+y

²-Si3N4 matrix composites reinforced with nano-meter scale SiC particles were fabricated by hot-pressing the mixture of SiC and Si3N4 fine powders. Interface microstructure and crack propagation in the composite were observed by high resolution electron microscopy. The interface between SiC and Si3N4 had good coherence, but no preferred orientation was observed. At the interface between SiC and Si3N4, the (111) face of SiC particles was flat, and sometimes a disturbed lattice structure thinner than 1 nm was observed. Near the main cracks, the microcracking at fine SiC particles/Si3N4 matrix interface was frequently observed. The cracks propagated exactly along this interface. The interface microcracking seems to contribute to the improvement of fracture toughness.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400451742

Interface Structure of Si3N4 Matrix Composite with Nano-Meter Scale SiC Particles

Crack propagation behavior of a chemical vapor deposited (CVD) Si 3 N 4 -TiN composite was investigated by microindentation fracture (MIF) and high-resolution electron microscopy (HREM) techniques. TiN fibers are homogeneously dispersed in large Si 3 N 4 grains (about 8 μm in diameter), leading to an intragranular nano-composite structure, and their interfaces were directly bonded without any other phases. The main fracture mode is a mixed type of intergranular and transgranular fracture. Nanometer-sized TiN dispersed in the matrix grauns interacts with cracks, generating crack bridging and microcracking which toughens the composite

Crack Propagation Behavior of CVD Si 3 N 4 –TiN Composite Examined by High-Resolution Electron Microscopy

Ordered structures in decagonal quasicrystals are discussed by the projection of five-dimensional periodic lattices on two-dimensional space. Superlattices in rhombic and pentagonal Penrose lattices can be derived from simple and body-centered hypercubic lattices, respectively. The superlattices are compared with ordered structures observed in Al–Ni–Co and Al–Ni–Ru decagonal quasicrystals in which two types of atom clusters with different orientations of pentagonal symmetry are placed at lattice points in pentagonal or rhombic quasiperiodic lattices with definite ordered manners.

Kenji Hiraga

Papers

Growth condition and x-ray analysis of single Al64Cu23Fe13 icosahedral quasicrystal by the Czochralski method

Tetragonal and orthorhombic phases of La2NiO4+y

Interface Structure of Si3N4 Matrix Composite with Nano-Meter Scale SiC Particles

Crack Propagation Behavior of CVD Si 3 N 4 –TiN Composite Examined by High-Resolution Electron Microscopy

Ordered structures in decagonal quasicrystals with simple and body-centered hypercubic lattices