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. ...

/pdf/a-comprehensive-review-of-zno-materials-and-devices-21a3zjadem.pdf

A comprehensive review of zno materials and devices

The unique characteristics of ultrafast lasers, such as picosecond and femtosecond lasers, have opened up new avenues in materials processing that employ ultrashort pulse widths and extremely high peak intensities. Thus, ultrafast lasers are currently used widely for both fundamental research and practical applications. This review describes the characteristics of ultrafast laser processing and the recent advancements and applications of both surface and volume processing. Surface processing includes micromachining, micro- and nanostructuring, and nanoablation, while volume processing includes two-photon polymerization and three-dimensional (3D) processing within transparent materials. Commercial and industrial applications of ultrafast laser processing are also introduced, and a summary of the technology with future outlooks are also given. Scientists in Asia have reviewed the role of ultrafast lasers in materials processing. Koji Sugioka from RIKEN in Japan and Ya Cheng from the Shanghai Institute of Optics and Fine Mechanics in China describe how femtosecond and picosecond lasers can be used to perform useful tasks in both surface and volume processing. Such lasers can cut, drill and ablate a variety of materials with high precision, including metals, semiconductors, ceramics and glasses. They can also polymerize organic materials that contain a suitable photosensitizer and can three-dimensionally process inside transparent materials such as glass, and are already being used to fabricate medical stents, repair photomasks, drill ink-jet nozzles and pattern solar cells. The researchers also explain the characteristics of such lasers and the interaction of ultrashort, intense pulses of light with matter.

/pdf/ultrafast-lasers-reliable-tools-for-advanced-materials-vf0u8o1rkp.pdf

Ultrafast lasers—reliable tools for advanced materials processing

Several hundred thousands of tons of ZnO are used by per year, e.g. as an additive to concrete or to rubber. In the field of optoelectronics, ZnO holds promises as a material for a blue/UV optoelectronics, alternatively to GaN, as a cheap, transparent, conducting oxide, as a material for electronic circuits, which are transparent in the visible or for semiconductor spintronics. The main problem is presently, however, a high, reproducible and stable p-doping. We review in this contribution partly critically the material growth, fundamental properties of ZnO and of ZnO-based nanostructures, doping as well as present and future applications, with emphasis on the electronic and optical properties including stimulated emission. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ZnO : From basics towards applications

ZnO is presently experiencing a research boom with more than 2000 ZnO-related publications in 2005. This phenomenon is triggered, for example, by hope to use ZnO as a material for blue/UV optoelectronics as an alternative to GaN, as a cheap, transparent, conducting oxide, as a material for electronic circuits that are transparent in the visible or for semiconductor spintronics. Currently, however, the main problem is to achieve high, reproducible and stable p-doping. Herein, we critically review aspects of the material growth, fundamental properties of ZnO and ZnO-based nanostructures and doping as well as present and future applications with emphasis on the electronic and optical properties including stimulated emission.

ZnO: Material, Physics and Applications

We show that short-pulse laser-induced classical ripples on dielectrics, semiconductors, and conductors exhibit a prominent "non-classical" characteristic-in normal incidence the periods are definitely smaller than laser wavelengths, which indicates that the simplified scattering model should be revised. Taking into account the surface plasmons (SPs), we consider that the ripples result from the initial direct SP-laser interference and the subsequent grating-assisted SP-laser coupling. With the model, the period-decreasing phenomenon originates in the admixture of the field-distribution effect and the grating-coupling effect. Further, we propose an approach for obtaining the dielectric constant, electron density, and electron collision time of the high-excited surface. With the derived parameters, the numerical simulations are in good agreement with the experimental results. On the other hand, our results confirm that the surface irradiated by short-pulse laser with damage-threshold fluence should behave metallic, no matter for metal, semiconductor, or dielectric, and the short-pulse laser-induced subwavelength structures should be ascribed to a phenomenon of nano-optics.

Origin of laser-induced near-subwavelength ripples: interference between surface plasmons and incident laser

We report the laser-induced periodic surface structure (LIPSS) with periodicity about a quarter of the laser wavelength on unpolished diamond film treated by a P-polarized femtosecond laser. The short period LIPSS is parallel to the laser polarization and independent on the incidence angle. The LIPSS perpendicular to the laser polarization with periodicity shorter than a third of the laser wavelength slightly dependent on the incidence angle is also observed as well as the LIPSS perpendicular to the laser polarization with periodicity dependent on the incidence angle. The results are explained by interference of the incident laser and surface scattered wave related to the excited electrons during laser interactions with diamond, being in excellent agreement with a previously developed theory.

Femtosecond laser-induced periodic surface structure on diamond film

We report on photoluminescence in a ZnO/GaN heterostructure, which showed a donor–acceptor pair emission band at 3.270 eV and the longitudinal optical phonon replicas at 12 K. In comparison with p-type GaN, the positions of the peaks are redshifted. This may be associated with the variation of the residual strain in the GaN layer of the heterostructure. Using this heterostructure, near-ultraviolet light-emitting diodes were fabricated and their electroluminescence properties were characterized.

Optical properties of ZnO/GaN heterostructure and its near-ultraviolet light-emitting diode

Micro-Raman spectroscopy was employed to investigate the structural changes of diamond films prepared by hot filament chemical vapor deposition and treated by femtosecond (fs) laser and nanosecond (ns) lasers. Breit–Wigner–Fano and Lorentzian line shape simulations were used to fit the spectra. For 266 nm ns laser treated samples, increasing laser power density results in the transformation of amorphous carbons in diamond films into nanocarbon clusters whose size increases and saturates rapidly at around 5.1 nm. At the same time, the Raman G peak position considerably shifts upwardly with increasing laser power density. The different change behavior of the nanocarbons and G peak is interpreted in light of the charge transfer from the graphite π bands to the localized edge states. As the 266 nm laser power density is high enough, a Raman peak in the range of 1150–1200 cm−1 appears, which is attributed to the presence of amorphous diamond. In the case of fs laser treated samples, much more power density (>1...

Raman investigation of amorphous carbon in diamond film treated by laser

Holes were percussion drilled in Inconel 718 plates by a high intensity pulsed ultraviolet laser (266 and 355 nm) with 8 ns pulse width. It showed that shortening the laser wavelength resulted in thinner recast layers, less microcracks, and faster machining speed. In order to get high quality and fast speed in laser hole drilling, a two-step processing method was proposed and tested.

Hole drilling of Inconel 718 by high intensity pulsed ultraviolet laser

Holes were percussion drilled in 1.5 mm thick INCONEL 718 plates at 30° angle from the surface using a state-of-the-art, pulsed, Q-Switched Nd: YAG laser. It showed that shortening the laser wavelength resulted in thinner recast layers, less microcracks, and much faster machining speeds. Ripple-like patterns were found on the hole-walls and a tentative explanation was given. The temperature distribution during laser hole drilling was simulated, and the materials removal rate, reflectivity and thermodynamic critical temperature were deduced from the simulations. A two-step processing method was proposed and tested to be effective. A new rotating quartz system was designed for drilling greater diameter holes and proved working well.Holes were percussion drilled in 1.5 mm thick INCONEL 718 plates at 30° angle from the surface using a state-of-the-art, pulsed, Q-Switched Nd: YAG laser. It showed that shortening the laser wavelength resulted in thinner recast layers, less microcracks, and much faster machining speeds. Ripple-like patterns were found on the hole-walls and a tentative explanation was given. The temperature distribution during laser hole drilling was simulated, and the materials removal rate, reflectivity and thermodynamic critical temperature were deduced from the simulations. A two-step processing method was proposed and tested to be effective. A new rotating quartz system was designed for drilling greater diameter holes and proved working well.

Hole drilling of Inconel 718 by high intensity pulsed UV laser

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