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5 Nov 2007

Volume 91, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 91, 191106 (2007); http://dx.doi.org/10.1063/1.2804016 (3 pages)

A. Pikulin, N. Bityurin, G. Langer, D. Brodoceanu, and D. Bäuerle
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Origins of high radiative efficiency and wideband emission from InAs quantum dots

C. Y. Ngo, S. F. Yoon, W. J. Fan, and S. J. Chua

Appl. Phys. Lett. 91, 191901 (2007); http://dx.doi.org/10.1063/1.2807269 (3 pages) | Cited 6 times

Online Publication Date: 5 November 2007

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Origins of high radiative efficiency and wideband emission from InAs quantum dots (QDs) were studied experimentally and theoretically. Radiative efficiency was found to depend strongly on the absence of large nonradiative islands. Theoretical calculations were performed to determine the combined effects of QD size and its fluctuation on the energy range. Good agreement between the theoretical and experimental results was obtained. Recognizing that high output power and large optical bandwidth are key figures of merit for QD superluminescent diodes (SLDs), we believe that the findings from our work will be beneficial for those working on QD-SLDs.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)

Electromigration-induced Coble creep in polycrystalline materials

Zhonghua Li, Yan Dong, Shu Li, Limin Xu, and Jun Sun

Appl. Phys. Lett. 91, 191902 (2007); http://dx.doi.org/10.1063/1.2805017 (3 pages) | Cited 7 times

Online Publication Date: 5 November 2007

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A simple expression has been derived for the prediction of the creep rate controlled by electromigration-induced grain boundary diffusion. The creep rate depends linearly on the current density and the grain boundary diffusivity, and inversely on grain size squared. It is also demonstrated that the electromigration-induced creep can be fully suppressed by a critical compressive stress gradient.
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81.40.Lm Deformation, plasticity, and creep
62.20.Hg Creep
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
66.30.Qa Electromigration
61.72.Mm Grain and twin boundaries
66.30.Lw Diffusion of other defects

Effects of different plasma species (atomic N, metastable N2*, and ions) on the optical properties of dilute nitride materials grown by plasma-assisted molecular-beam epitaxy

Michael M. Oye, Terry J. Mattord, Gary A. Hallock, Seth R. Bank, Mark A. Wistey, Jason M. Reifsnider, Aaron J. Ptak, Homan B. Yuen, James S. Harris, Jr., and Archie L. Holmes, Jr.

Appl. Phys. Lett. 91, 191903 (2007); http://dx.doi.org/10.1063/1.2806226 (3 pages) | Cited 5 times

Online Publication Date: 6 November 2007

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This letter studies the effects of atomic N, metastable N2*, and ionic species on the optical properties of dilute nitride materials. Ga0.8In0.2N0.01As0.99 was grown using a 1% N2 in Ar gas mix from an Applied-Epi Unibulb™ rf plasma source. Isonitrogen samples with and without ions were studied using various plasma operating conditions. Optical emission spectrometry was used to characterize relative proportions of different active nitrogen plasma species (atomic N and metastable N2*). Samples grown without ions and with a higher proportion of atomic N resulted in the best overall material quality, although this improvement was observed at high annealing temperatures. At lower annealing temperatures, increased blueshifts were observed for samples grown with a higher proportion of atomic N; however, there was no noticeable influence of ions on blueshift regardless of whether atomic N or metastable N2* was the dominant species present in the plasma. The key implication of this work is that it helps to elucidate a possible reason for some of the contradictory reports in the literature. The ions are not solely responsible for the commonly reported “plasma damage.” Furthermore, we demonstrate herein that atomic N and metastable N2* each have different effects on the optical properties of dilute nitride materials grown by plasma-assisted molecular-beam epitaxy.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.-j Plasma applications

Elastic properties of Fe–Mn random alloys studied by ab initio calculations

Denis Music, Tetsuya Takahashi, Levente Vitos, Christian Asker, Igor A. Abrikosov, and Jochen M. Schneider

Appl. Phys. Lett. 91, 191904 (2007); http://dx.doi.org/10.1063/1.2807677 (3 pages) | Cited 12 times

Online Publication Date: 8 November 2007

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We have studied the influence of the Mn content on the elastic properties of Fe–Mn random alloys (space group of Fmmathm) using ab initio calculations. The magnetic effects in Fe–Mn alloys have a strong influence on the elastic properties, even above the Néel temperature. As the Mn content is increased from 5 to 40 at. %, the C44 elastic constant is unaffected, while C11 and C12 decrease. This behavior can be understood based on the magnetovolume effect which softens the lattice. Since the amplitude of local magnetic moments is less sensitive to volume conserving distortions, the softening is not present during shearing.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Cr Saturation moments and magnetic susceptibilities

Growth of a-plane GaN on lattice-matched ZnO substrates using a room-temperature buffer layer

Atsushi Kobayashi, Satoshi Kawano, Kohei Ueno, Jitsuo Ohta, Hiroshi Fujioka, Hidetaka Amanai, Satoru Nagao, and Hideyoshi Horie

Appl. Phys. Lett. 91, 191905 (2007); http://dx.doi.org/10.1063/1.2809361 (3 pages) | Cited 8 times

Online Publication Date: 8 November 2007

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Nonpolar a-plane GaN films were grown on nearly lattice-matched a-plane ZnO substrates by pulsed laser deposition. Growth of GaN on a-plane ZnO at conventional growth temperatures (around 700 °C) resulted in the formation of polycrystalline materials, probably due to the interface reactions between GaN and ZnO. However, single crystalline a-plane GaN with an atomically flat surface can be grown on ZnO at room temperature in the layer-by-layer mode. X-ray diffraction and photoluminescence measurements revealed that high-quality a-plane GaN films can also be grown at elevated substrate temperatures (up to 700 °C) by using a RT a-plane GaN film as a buffer layer.
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81.15.Fg Pulsed laser ablation deposition
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Formation and reduction of pyramidal hillocks on m-plane {1math00} GaN

A. Hirai, Z. Jia, M. C. Schmidt, R. M. Farrell, S. P. DenBaars, S. Nakamura, J. S. Speck, and K. Fujito

Appl. Phys. Lett. 91, 191906 (2007); http://dx.doi.org/10.1063/1.2802570 (3 pages) | Cited 19 times

Online Publication Date: 8 November 2007

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Surface morphology and hillock reduction were studied on m-plane {1math00} n-type GaN films and light emitting diode structures grown by metal organic chemical vapor deposition on low defect-density m-plane GaN substrates. For nominally on-axis m-plane films, predominantly pyramidal hillocks were observed, which were composed of two faces symmetrically inclined by 0.1°–0.25° to the ±[11math0] a direction and two faces inclined by 0.5°–0.95° to the [000math] c− and the [0001] c+ directions, respectively. All faces of the pyramidal hillocks for the nominally on-axis GaN films had clearly defined step-terrace structures. Gradual changes in nominal miscut angles from 0° to 10° along the a and the c− directions succeeded in a continuous hillock reduction yielding atomically flat surfaces.
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68.55.-a Thin film structure and morphology
68.60.-p Physical properties of thin films, nonelectronic
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Population dynamics of localized biexcitons in AlxGa1−xN ternary alloys

Yoichi Yamada, Hideaki Murotani, Tsunemasa Taguchi, Akihiko Ishibashi, Yasutoshi Kawaguchi, and Toshiya Yokogawa

Appl. Phys. Lett. 91, 191907 (2007); http://dx.doi.org/10.1063/1.2812525 (3 pages) | Cited 1 time

Online Publication Date: 9 November 2007

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Dynamical behavior of localized biexcitons in Ga-rich AlxGa1−xN ternary alloys has been studied by means of time-resolved luminescence spectroscopy. The time-dependent luminescence was analyzed using rate equations which were modified by considering the localization times of both the biexcitons and single excitons individually. The localization times of both biexcitons and single excitons became longer with increasing aluminum composition. On the other hand, the formation time of biexcitons from single excitons remained nearly unchanged. This observation indicated that the formation rate of biexcitons in the ternary alloys was independent of the localization depth of single excitons.
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71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors

Time-resolved thermal mirror for nanoscale surface displacement detection in low absorbing solids

N. G. C. Astrath, L. C. Malacarne, P. R. B. Pedreira, A. C. Bento, M. L. Baesso, and J. Shen

Appl. Phys. Lett. 91, 191908 (2007); http://dx.doi.org/10.1063/1.2812542 (3 pages) | Cited 16 times

Online Publication Date: 9 November 2007

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A time-resolved thermal mirror method for measurements of absolute thermo-optical-mechanical properties of low absorbing solids is presented. The thermoelastic equation for the surface displacement and an analytical expression for the probe beam intensity at the detector plane were derived. Experimental proofs were performed in an optical glass and the fitted parameters are in good agreement with previous literature data for thermal, optical, and mechanical properties, suggesting that the method is a useful tool for the characterization of a wide range of transparent materials.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
42.70.Ce Glasses, quartz
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Jj Elasticity and anelasticity, stress-strain relations

Annealing of dilute-nitride GaAsSbN/InP strained multiple quantum wells

D. P. Xu, J. Y. T. Huang, J. Park, L. J. Mawst, T. F. Kuech, X. Song, and S. E. Babcock

Appl. Phys. Lett. 91, 191909 (2007); http://dx.doi.org/10.1063/1.2805637 (3 pages)

Online Publication Date: 9 November 2007

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The thermal annealing of GaAsSbN/InP strained multiple quantum wells (MQWs) grown by metal organic chemical vapor deposition was investigated. Photoluminescence peak intensity and linewidth changes indicate a significant improvement in optical quality of the GaAsSbN/InP MQWs upon annealing. We find no significant annealing-induced blueshift of the optical transitions, which confirms the theoretical expectation that a change in the nearest-neighbor configuration nitrogen atoms has negligible effect on the band gap of GaAsSbN. The evolution of (400) x-ray diffraction rocking curves with thermal treatment of the samples was consistent with the constituent redistribution in the GaAsSbN QW.
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81.07.St Quantum wells
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
78.67.De Quantum wells
78.55.Cr III-V semiconductors
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