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26 Mar 2007

Volume 90, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 90, 134101 (2007); http://dx.doi.org/10.1063/1.2679209 (3 pages)

S. Srinivasan, J. Hiller, B. Kabius, and O. Auciello
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Annealing kinetics of nanoindentation-induced polycrystalline high pressure phases in crystalline silicon

S. Ruffell, J. E. Bradby, and J. S. Williams

Appl. Phys. Lett. 90, 131901 (2007); http://dx.doi.org/10.1063/1.2716854 (3 pages) | Cited 9 times

Online Publication Date: 26 March 2007

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Transformation kinetics of nanoindented zones in silicon containing high pressure crystalline phases (Si III and Si XII) during annealing (100 °C<T<450 °C) have been studied using Raman microspectroscopy and cross-sectional transmission electron microscopy. Signature peaks associated with Si III/XII in the Raman spectra were monitored to track the annealing of these phases to polycrystalline Si I as a function of annealing time and temperature. An overall activation energy for this transformation was found to be 0.67 eV. During annealing, Si XII disappeared faster than Si III, suggesting either that Si XII first converts to Si III or that Si XII transforms to polycrystalline Si I faster than Si III.
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64.70.K- Solid-solid transitions
61.72.Cc Kinetics of defect formation and annealing
62.50.-p High-pressure effects in solids and liquids
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
78.30.Hv Other nonmetallic inorganics

Ultrasonic attenuation properties of glassy alloys in views of complex viscoelasticity

Mikio Fukuhara, Wei Zhang, Dmitri V. Louzguine-Luzgin, Akihisa Inoue, and Nobuyuki Nishiyama

Appl. Phys. Lett. 90, 131902 (2007); http://dx.doi.org/10.1063/1.2716862 (3 pages) | Cited 3 times

Online Publication Date: 26 March 2007

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Using ultrasonics, acoustic attenuation characteristics of Pd40Cu30P20Ni10, Zr65Pd12.5Ni10Al7.5Cu5, Cu55Zr30Ti10Pd5, and Ti41.5Cu47.5Ni7.5Hf5Zr2.5Sn1 glassy alloys were examined in comparison with crystalline metals based on complex viscoelasticity. The glassy alloys favor to absorb the longitudinal one, but crystalline materials absorb the shear one, associated with periodicity and randomness of energy potentials, respectively. In sharp contrast to crystalline materials, Nyquist [Bell Syst. Tech. J. 11, 126 (1932) ] diagrams of the glassy alloys are characterized by large areas of the third and the fourth quadrant in the loop, suggesting advancement of the relay in phase, that is, increment of the imaginary parts in complex waves.
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62.65.+k Acoustical properties of solids
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations

Photoluminescence of Si-rich silicon nitride: Defect-related states and silicon nanoclusters

Minghua Wang, Dongsheng Li, Zhizhong Yuan, Deren Yang, and Duanlin Que

Appl. Phys. Lett. 90, 131903 (2007); http://dx.doi.org/10.1063/1.2717014 (3 pages) | Cited 19 times

Online Publication Date: 26 March 2007

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The photoluminescence (PL) from defect-related states and Si nanoclusters was observed in the Si-rich silicon nitride films simultaneously. The weaker red-light emission of Si nanoclusters was obtained in the 1100 °C annealed films with the 514.5 nm excitation. Due to the quantum confinement effect, the PL peaks redshift with the increase of the excess Si concentration. Excited by the 325 nm line, strong PL from N and Si dangling bond centers was observed in either the as-deposited films or the 1100 °C annealed ones. The results demonstrate that the luminescence from defect-related states or Si nanoclusters is selected by the excitation energy.
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78.55.Hx Other solid inorganic materials
78.66.-w Optical properties of specific thin films
71.55.Ht Other nonmetals
81.40.Gh Other heat and thermomechanical treatments

Molecular statics calculation of the formation enthalpy for ternary metal systems based on the long-range empirical interatomic potentials

X. D. Dai, J. H. Li, and B. X. Liu

Appl. Phys. Lett. 90, 131904 (2007); http://dx.doi.org/10.1063/1.2716361 (3 pages) | Cited 6 times

Online Publication Date: 27 March 2007

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A scheme is proposed in the present study to predict the formation enthalpy of the ternary metal system. Based on the long-range empirical potential model, the interatomic potentials are first constructed for the Cu–Ag–Au, Cu–Ag–Ni, Ag–Au–Ni, and Cu–Au–Ni systems, and then molecular statics calculations are performed to predict the formation enthalpies of the four systems. It is found that the predicted results by the present scheme match well with those obtained by experiments or ab initio calculations, exhibiting a more precise feature than Miedema’s model.
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82.60.Cx Enthalpies of combustion, reaction, and formation
65.40.G- Other thermodynamical quantities

Conduction band offset for Ga0.62In0.38NxAs0.991−xSb0.009/GaNyAs1−y/GaAs systems with the ground state transition at 1.5–1.65 μm

R. Kudrawiec, S. R. Bank, H. B. Yuen, H. Bae, M. A. Wistey, L. L. Goddard, James S. Harris, Jr., M. Gladysiewicz, M. Motyka, and J. Misiewicz

Appl. Phys. Lett. 90, 131905 (2007); http://dx.doi.org/10.1063/1.2716366 (3 pages) | Cited 5 times

Online Publication Date: 27 March 2007

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Conduction band offset for Ga0.62In0.38NxAs0.991−xSb0.009/GaNyAs1−y/GaAs systems with different N contents (x = 2.2%–3.0% and y = 3.1%–4.3% of N) has been investigated by contactless electroreflectance spectroscopy supported by theoretical calculations performed within the effective mass approximation. It has been found that Ga0.62In0.38NxAs0.991−xSb0.009/GaNyAs1−y quantum wells (QWs) are promising for laser applications from the point of view of carrier confinement since the conduction band offset (QC) for these QWs is between 70% and 75%. In addition, it has been shown that GaNAs/GaAs interface is type I with QC between 80% and 90%.
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73.21.Fg Quantum wells
71.30.+h Metal-insulator transitions and other electronic transitions
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
78.67.De Quantum wells
78.20.Jq Electro-optical effects

Measurement of carrier concentration captured by InAs/GaAs quantum dots using terahertz time-domain spectroscopy

Seung Jae Oh, Chul Kang, Inhee Maeng, Joo-Hiuk Son, Nam Ki Cho, Jin Dong Song, Won Jun Choi, Woon-Jo Cho, and Jung Il Lee

Appl. Phys. Lett. 90, 131906 (2007); http://dx.doi.org/10.1063/1.2716859 (3 pages) | Cited 8 times

Online Publication Date: 27 March 2007

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The authors investigated the carrier dynamics of n-type modulation-doped InAs/GaAs quantum dots (QDs) using terahertz time-domain spectroscopy to estimate the total number of electrons captured by the QDs. The terahertz power absorption of the sample with QDs was less than that of the sample without QDs. This is attributed to the fact that the carriers are confined in the QDs. The experiment results were fitted into the Drude model and the number of electrons captured by QDs was determined through the difference in the numbers of free electrons of the samples with and without QDs.
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73.63.Kv Quantum dots
78.67.Hc Quantum dots
78.70.Gq Microwave and radio-frequency interactions
72.20.Fr Low-field transport and mobility; piezoresistance
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Well-width-dependent carrier lifetime in AlGaN/AlGaN quantum wells

J. Mickevičius, G. Tamulaitis, E. Kuokštis, K. Liu, M. S. Shur, J. P. Zhang, and R. Gaska

Appl. Phys. Lett. 90, 131907 (2007); http://dx.doi.org/10.1063/1.2717145 (3 pages) | Cited 7 times

Online Publication Date: 27 March 2007

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A set of Al0.35Ga0.65N/Al0.49Ga0.51N multiple quantum wells (MQWs) with fixed barrier width and well widths varying from 1.65 to 5.0 nm has been grown by metal-organic chemical vapor deposition. Carrier dynamics in the MQWs were studied using time-resolved photoluminescence (PL) spectroscopy and light-induced transient grating (four wave mixing) technique. The authors observed that the lifetime of nonequilibrium carriers (excitons) increases with decreasing well width and interpreted the effect by stronger localization preventing their migration to nonradiative recombination centers. Meanwhile the radiative decay time is also influenced by screening of the built-in electric field, which spatially separates the electrons and holes. It is shown that this effect affects the initial part of PL intensity decay after pulsed excitation. It becomes more pronounced with increase in the initial carrier density but saturates when the carrier density is high enough to completely screen the built-in electric field. The screening effect on PL decay is stronger in wider quantum wells.
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73.63.Hs Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.67.De Quantum wells
78.55.Cr III-V semiconductors
73.21.Fg Quantum wells
78.47.-p Spectroscopy of solid state dynamics
71.35.-y Excitons and related phenomena

Direct comparison of optical characteristics of InGaN-based laser diode structures grown on pendeo epitaxial GaN and sapphire substrates

J. S. Hwang, A. Gokarna, Yong-Hoon Cho, J. K. Son, S. N. Lee, T. Sakong, H. S. Paek, O. H. Nam, and Y. Park

Appl. Phys. Lett. 90, 131908 (2007); http://dx.doi.org/10.1063/1.2716313 (3 pages) | Cited 3 times

Online Publication Date: 28 March 2007

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Direct comparison of optical properties and carrier dynamics of InGaN multiple quantum well (MQW) laser diode structures grown on pendeo epitaxial (PE)-GaN and sapphire substrates is reported. A strong increase in quantum efficiency and a dramatic reduction in stimulated emission threshold are observed for InGaN MQWs on PE-GaN substrates as compared to MQWs on sapphire substrates. Based on temperature-dependent time-resolved optical analysis, the authors find that a significant increase in nonradiative lifetime due to suppressed dislocation density plays an important role in enhancing optical properties of InGaN MQWs grown on PE-GaN substrates, resulting in radiative-process dominant emission even at room temperature.
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42.55.Px Semiconductor lasers; laser diodes

Plasma-assisted molecular-beam epitaxy of AlN(11math2) on m sapphire

L. Lahourcade, E. Bellet-Amalric, E. Monroy, M. Abouzaid, and P. Ruterana

Appl. Phys. Lett. 90, 131909 (2007); http://dx.doi.org/10.1063/1.2716375 (3 pages) | Cited 24 times

Online Publication Date: 28 March 2007

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The authors report on the plasma-assisted molecular-beam epitaxy of semipolar AlN(11math2) films on (1math00) m-plane sapphire. AlN deposited on m sapphire settles into two main crystalline orientation domains, AlN(11math2) and AlN(10math0), whose ratio depends on the III/V ratio. The in-plane epitaxial relationships of AlN(11math2) on m-plane sapphire are [11mathmath]AlN‖[0001]sapphire and [1math00]AlN‖[11math0]sapphire. In the case of AlN(10math0), the in-plane epitaxial relationships were [1math10]AlN‖[0001]sapphire and [0001]AlN‖[11math0]sapphire. Growth under moderate nitrogen-rich conditions enables them to isolate the (11math2) orientation and to improve the surface morphology of the layers.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.-j Plasma applications
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)

Mechanism for the ablation of Si⟨111⟩ with pairs of ultrashort laser pulses

Zhan Hu, Sima Singha, Yaoming Liu, and Robert J. Gordon

Appl. Phys. Lett. 90, 131910 (2007); http://dx.doi.org/10.1063/1.2716838 (3 pages) | Cited 14 times

Online Publication Date: 28 March 2007

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Pairs of ultrafast laser pulses are used to ablate Si⟨111⟩. The fluorescence from Si atoms and ions was observed to increase by an order of magnitude as the delay between the pulses was increased. From the dependence of the fluorescence enhancement on the laser fluence and the pulse delay, it is deduced that the first pulse melts the surface and that the second pulse interacts more strongly with the liquid phase.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
61.82.Fk Semiconductors
78.55.Ap Elemental semiconductors

Real-time observation of oxidation and photo-oxidation of rubrene thin films by spectroscopic ellipsometry

M. Kytka, A. Gerlach, F. Schreiber, and J. Kováč

Appl. Phys. Lett. 90, 131911 (2007); http://dx.doi.org/10.1063/1.2717561 (3 pages) | Cited 24 times

Online Publication Date: 29 March 2007

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The authors follow in real time and under controlled conditions the oxidation of the organic semiconductor rubrene grown on SiO2 using spectroscopic ellipsometry. They derive the complex dielectric function ε1+iε2 for pristine and oxidized rubrene showing that the oxidation is accompanied by a significant change of the optical properties, namely, the absorption. The authors observe that photo-oxidation of rubrene is orders of magnitude faster than oxidation without illumination. By following different absorption bands (around 2.5 and 4.0 eV for pristine rubrene and around 4.9 eV for oxidized rubrene) they infer that the observed photo-oxidation of these films involves non-Fickian diffusion mechanisms.
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78.66.Qn Polymers; organic compounds
82.30.-b Specific chemical reactions; reaction mechanisms
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Me Organic compounds and polymers

Deformation of glass forming metallic liquids: Configurational changes and their relation to elastic softening

John S. Harmon, Marios D. Demetriou, William L. Johnson, and Min Tao

Appl. Phys. Lett. 90, 131912 (2007); http://dx.doi.org/10.1063/1.2717017 (3 pages) | Cited 9 times

Online Publication Date: 30 March 2007

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The change in the configurational enthalpy of metallic glass forming liquids induced by mechanical deformation and its effect on elastic softening is assessed. The acoustically measured shear modulus is found to decrease with increasing configurational enthalpy by a dependence similar to one obtained by softening via thermal annealing. This establishes that elastic softening is governed by a unique functional relationship between shear modulus and configurational enthalpy.
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81.05.Kf Glasses (including metallic glasses)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.10.+s Mechanical properties of liquids
65.20.-w Thermal properties of liquids

Existence of tetrahedral site symmetry about Ge atoms in a single-crystal film of Ge2Sb2Te5 found by x-ray fluorescence holography

S. Hosokawa, T. Ozaki, K. Hayashi, N. Happo, M. Fujiwara, K. Horii, P. Fons, A. V. Kolobov, and J. Tominaga

Appl. Phys. Lett. 90, 131913 (2007); http://dx.doi.org/10.1063/1.2717094 (3 pages) | Cited 11 times

Online Publication Date: 30 March 2007

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The authors discuss x-ray fluorescence holography (XFH) measurements taken from an epitaxial layer of the digital versatile disk random access memory (DVD-RAM) material Ge2Sb2Te5 grown on a single-crystal GaSb(100) substrate. By using fluorescent photons from the Ge atoms in the matrix, a three-dimensional atomic image was obtained around the Ge atoms in a Ge2Sb2Te5 film; details of the three-dimensional atomic arrangement will aim at clarification of the high-speed writing and erasing mechanism of the laser-induced crystal-amorphous phase transition in this DVD-RAM material. Analysis of the XFH images revealed that the epitaxial layer did not possess a hexagonal structure as in the equilibrium phase of Ge2Sb2Te5, but a cubic structure with tetrahedral site symmetry about Ge atoms, different from the previous powder diffraction result. The present structure may support the umbrella-flip model of the Ge atoms between the octahedral site in the distorted rocksalt crystal and the tetrahedral site in the amorphous phase on the laser-induced phase transition.
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42.70.Ln Holographic recording materials; optical storage media
42.79.Wc Optical coatings
42.79.Vb Optical storage systems, optical disks
84.30.Sk Pulse and digital circuits
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