High temperature excitonic stimulated emission from ZnO epitaxial layers
TL;DR: In this paper, the emission spectrum of high quality ZnO epilayers is studied from room temperature up to 550 K. At room temperature and low excitation power, a single emission peak is observed which may be identified with the free exciton from its peak energy and dependence on temperature.
Abstract: The emission spectrum of high quality ZnO epilayers is studied from room temperature up to 550 K. At room temperature and low excitation power a single emission peak is observed which may be identified with the free exciton from its peak energy and dependence on temperature. However, when excitation intensities exceed 400 kW cm−2 a sharp peak emerges at lower energy which we attribute to exciton-exciton scattering. At higher excitation intensities (>800 kW cm−2) a second stimulated emission peak emerges at even lower energies: we attribute this peak to be stimulated emission of an electron hole plasma. Similar features are observed for all temperatures up to 550 K.
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TL;DR: 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.
Abstract: 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. ...
10,260 citations
TL;DR: In this article, the unidirectional growth of the ZnO nanowires was controlled by the conventional vapor-liquid solid mechanism, and the observed room temperature UV emission was ascribed to the decrease in structure defects as compared to bulk materials.
Abstract: ZnO nanowires were mass produced using a physical vapor deposition approach. The ZnO nanowire monocrystallites have an average diameter around 60 nm and length up to a few micrometers. The unidirectional growth of the ZnO nanowires was controlled by the conventional vapor-liquid-solid mechanism. Intensive UV light emission peaked around 3.27 eV was observed at room temperature, which was assigned to emission from free exciton under low excitation intensity. The observed room temperature UV emission was ascribed to the decrease in structure defects as compared to bulk ZnO materials, and in particularly to the size effect in the ZnO wires.
1,282 citations
TL;DR: In this paper, the results of Schottky UV photodetectors fabricated on n-type ZnO epitaxial films were presented, which were grown on R-plane sapphire substrates by metalorganic chemical vapor deposition.
889 citations
TL;DR: In this article, the authors review the 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.
Abstract: 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)
872 citations
TL;DR: This work 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.
Abstract: 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.
796 citations
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TL;DR: In this paper, the authors reported the observation of optically pumped lasing in ZnO at room temperature using a plasma-enhanced molecular beam epitaxy on sapphire substrates.
Abstract: We report the observation of optically pumped lasing in ZnO at room temperature. Thin films of ZnO were grown by plasma-enhanced molecular beam epitaxy on (0001) sapphire substrates. Laser cavities formed by cleaving were found to lase at a threshold excitation intensity of 240 kW cm−2. We believe these results demonstrate the high quality of ZnO epilayers grown by molecular beam epitaxy while clearly demonstrating the viability of ZnO based light emitting devices.
2,126 citations
TL;DR: In this article, a new three-parameter fit to the temperature dependence of semiconductor band gaps was proposed, based on the semi-empirical Varshni equation.
Abstract: In this letter we advocate the use of a new three-parameter fit to the temperature dependence of semiconductor band gaps. This fitting improves upon the semi-empirical Varshni equation* both numerically, since it gives better fits to the data, and theoretically, since the parameters of the fit may be related to an intrinsic interaction of semiconductors, namely the electron-phonon coupling. Similar expressions to ours have appeared in the literature2T3 but the practical and theoretical justification of this kind of data fit have not previously been worked out in detail. We emphasize that our approach is empirical: we aim simply to describe the data as well as possible with the minimum number of free parameters. The Varshni relation for the temperature dependence of semiconductor band gaps is Eg(T)=Eo--cYT2/(T+pA (1)
1,010 citations
TL;DR: In this paper, room temperature free excition absorption and luminescence were observed in ZnO thin films grown on sapphire substrates by the laser molecular beam epitaxy technique.
925 citations
TL;DR: In this paper, the light emission of ZnO under high one and two-quantum excitation was investigated in the temperature region from 4 to 300 K. Emission bands are observed which can be attributed to the interactions of free excitons with phonons, free excITons and free electrons, and of bound exciton with phonon and free and bound electrons.
Abstract: The light emission of ZnO under high one- and two-quantumexcitation is investigated in the temperature region from 4 to 300 K. Emission bands are observed which can be attributed to the interactions of free excitons with phonons, free excitons and free electrons, and of bound excitons with phonons and free and bound electrons.
Die Lichtemission von ZnO-Kristallen bei starker Bin- und Zweiquantenanregung wird im Temperaturbereich von 4 bis 300 K untersucht. Dabei werden Emissionsbanden beob-achtet, die zuruckgefuhrt werden konnen auf die Wechselwirkungen von freien Exzitonen mit Phononen, freien Exzitonen und freien Elektronen und von gebundenen Exzitonenmit Phononen und freien und gebundenen Elektronen.
553 citations
TL;DR: The nonlinear optical polarizability is shown to be greatly enhanced for an assembly of such microcrystallites as the exciton is quantized due to the confinement effect and the excitons in a single microCrystallite interact strongly enough to make theexcitons deviate from ideal harmonic oscillators.
Abstract: We analyze theoretically the oscillator strength and the third-order optical polarizability X 13, due to excitons in semiconductor microcrystallites. The nonlinear optical polarizability is shown to be greatly enhanced for an assembly of such microcrystallites as the exciton is quantized due to the confinement effect and the excitons in a single microcrystallite interact strongly enough to make the excitons deviate from ideal harmonic oscillators.
540 citations