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19 Mar 2007

Volume 90, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 123101 (2007); http://dx.doi.org/10.1063/1.2716242 (3 pages)

G. Z. Shen, Y. Bando, J. Q. Hu, and D. Golberg
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Reduced threshold current in (111)B grown InGaAs/AlGaAs laser diodes: The positive role of piezoelectric effect

G. Deligeorgis, G. Dialynas, Z. Hatzopoulos, and N. T. Pelekanos

Appl. Phys. Lett. 90, 121126 (2007); http://dx.doi.org/10.1063/1.2716214 (3 pages) | Cited 2 times

Online Publication Date: 22 March 2007

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The authors demonstrate that (111)B grown InGaAs/AlGaAs laser diodes outperform their (100) counterparts, in terms of lower threshold currents observed for all temperature and cavity lengths tested. A low temperature threshold current density as low as 15 A/cm2 has been observed in (111)B grown devices, whereas identical (100) laser diodes exhibited threshold in the range of 30–40 A/cm2. The comparison of experimental findings with a Poisson-Schrödinger self-consistent model reveals that the improved performance of the (111)B devices is attributed to the piezoelectric field present in the (111)B In0.1Ga0.9As active quantum well as well as to the different heavy hole effective masses in the (111)B configuration.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
77.65.-j Piezoelectricity and electromechanical effects

Frequency-agile terahertz-wave spectrometer for high-resolution gas sensing

Ruixiang Guo, Koichi Akiyama, Hiroaki Minamide, and Hiromasa Ito

Appl. Phys. Lett. 90, 121127 (2007); http://dx.doi.org/10.1063/1.2716146 (3 pages) | Cited 15 times

Online Publication Date: 23 March 2007

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A tabletop, frequency-agile terahertz-wave spectrometer was developed based on an injection-seeded terahertz-wave parametric generator. High-resolution (<100 MHz) spectra of polar gases can be measured in a wide frequency region (0.6–2.4 THz) within a short time (several minutes) with this spectrometer. To demonstrate the potential of this system, the authors performed real-time detection of the absorption line due to rotational transitions of the water molecule and determined their pressure-broadening coefficient.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants

Realization of ultraviolet electroluminescence from ZnO homojunction with n-ZnO/p-ZnO:As/GaAs structure

J. C. Sun, J. Z. Zhao, H. W. Liang, J. M. Bian, L. Z. Hu, H. Q. Zhang, X. P. Liang, W. F. Liu, and G. T. Du

Appl. Phys. Lett. 90, 121128 (2007); http://dx.doi.org/10.1063/1.2716206 (3 pages) | Cited 66 times

Online Publication Date: 23 March 2007

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ZnO homojunction light-emitting diode with n-ZnO/p-ZnO:As/GaAs structure is produced by metal organic chemical vapor deposition. The p-type ZnO:As film is obtained out of thermal diffusion of arsenic from GaAs substrate with subsequent thermal annealing at 550 °C. The n-type layer is composed of unintentionally doped ZnO film. Desirable rectifying behavior is observed from the current-voltage curve of the ZnO p-n homojunction. Furthermore, two distinct electroluminescence bands centered at 3.2 and 2.5 eV are obtained from the junction under forward bias at room temperature.
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85.60.Jb Light-emitting devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Cc Kinetics of defect formation and annealing

Focal tunable liquid lens integrated with an electromagnetic actuator

Seok Woo Lee and Seung S. Lee

Appl. Phys. Lett. 90, 121129 (2007); http://dx.doi.org/10.1063/1.2716213 (3 pages) | Cited 26 times

Online Publication Date: 23 March 2007

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In this letter, a focal tunable liquid lens using a large deformable polydimethylsiloxane (PDMS) membrane is integrated with an electromagnetic microactuator for uniform pressure on the membrane by a fabrication process of PDMS compatible with conventional micromachining processes. The fabricated device is characterized by surface profiling and optical observations. A rectangular PDMS membrane of 3 mm in width for actuation shows that the maximum displacement is 51.4 μm when the current is 30 mA. In the optical observations, the image is blurred when the applied current is varied. From the result, it was found that the device changes the focal length.
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42.79.Bh Lenses, prisms and mirrors
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.86.+b Optical workshop techniques
42.87.-d Optical testing techniques

Energy and momentum deposition from pulsed optical lattices to nonionized gases

Cedrick Ngalande, Sergey F. Gimelshein, and Mikhail N. Shneider

Appl. Phys. Lett. 90, 121130 (2007); http://dx.doi.org/10.1063/1.2716335 (3 pages) | Cited 6 times

Online Publication Date: 23 March 2007

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Nonresonant interaction of an optical lattice created by two counterpropagating laser fields with gas molecules is studied with the direct simulation Monte Carlo method. Energy and momentum deposition from lattice to gas in the collision regime are examined and the ability of a lattice to increase gas temperature to thousands of kelvins in a single pulse is shown.
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33.80.-b Photon interactions with molecules
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

Mid-infrared imaging with a solid immersion lens and broadband laser source

Chris A. Michaels

Appl. Phys. Lett. 90, 121131 (2007); http://dx.doi.org/10.1063/1.2716337 (3 pages) | Cited 7 times

Online Publication Date: 23 March 2007

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The application of hemispherical solid immersion lenses (SILs) is an approach to increasing the spatial resolution attainable with infrared (IR) microscopy. A hemispherical SIL forms an image for which the effective numerical aperture and magnification are increased by a factor of the SIL material index of refraction. A microscope designed for exploration of IR SIL imaging based on a hemispherical ZnSe SIL, an InSb focal plane array detector, and a broadband IR laser source is described. The imaging characteristics of this system are reported, including the spatial resolution improvement achieved in the imaging of organic test samples.
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42.79.Bh Lenses, prisms and mirrors
07.60.Pb Conventional optical microscopes
42.15.Eq Optical system design
42.79.Pw Imaging detectors and sensors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
42.72.Ai Infrared sources

Two-photon passive electro-optic upconversion in a GaAs/AlGaAs heterostructure device

Lai Zhao, Pete Thompson, N. N. Faleev, D. W. Prather, and Ian Appelbaum

Appl. Phys. Lett. 90, 121132 (2007); http://dx.doi.org/10.1063/1.2716354 (3 pages) | Cited 3 times

Online Publication Date: 23 March 2007

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A semiconductor heterostructure device that requires no external power source to upconvert two low-energy photons into one higher-energy photon is proposed. This passive device is fabricated in the AlGaAs/GaAs material system and it is used to demonstrate photon upconversion from 808 to 710 nm at room temperature.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.20.Jq Electro-optical effects

One-way total reflection with one-dimensional magneto-optical photonic crystals

Zongfu Yu, Zheng Wang, and Shanhui Fan

Appl. Phys. Lett. 90, 121133 (2007); http://dx.doi.org/10.1063/1.2716359 (3 pages) | Cited 38 times

Online Publication Date: 23 March 2007

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The authors show that one-dimensional magneto-optical photonic crystals can achieve one-way total reflection. The unit cell of the crystal, which consists of two bismuth iron garnet layers with opposite magnetization and one SiO2 layer, is designed to simultaneously break time-reversal, spatial inversion, and mirror symmetries. Such crystals are important for creating compact broadband optical isolators.
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42.70.Qs Photonic bandgap materials
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High peak-power (10.5 W) GaInAs/AlGaAsSb quantum-cascade lasers emitting at λ ∼ 3.6–3.8 μm

Quankui Yang, Christian Manz, Wolfgang Bronner, Nico Lehmann, Frank Fuchs, Klaus Köhler, and Joachim Wagner

Appl. Phys. Lett. 90, 121134 (2007); http://dx.doi.org/10.1063/1.2716363 (3 pages) | Cited 9 times

Online Publication Date: 23 March 2007

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High peak-power operation of quaternary-barrier GaInAs/AlGaAsSb quantum-cascade lasers emitting at λ ∼ 3.6–3.8 μm is reported. With as-cleaved facets, the lasers (18 μm×2.7 mm) emit a maximum peak power of 8.2 W per facet at 77 K. When applying a high-reflection coating to the back facet, a maximum peak power emitted from the front facet of 10.5 W at 77 K has been obtained for an 18 μm×2.0 mm device. The lasers operate in pulsed mode up to 340 K, and their emission wavelength shifts from 3.65 μm at 77 K to 3.79 μm at 300 K.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Spectral and spatial single mode emission from a photonic crystal distributed feedback laser

H. Hofmann, H. Scherer, S. Deubert, M. Kamp, and A. Forchel

Appl. Phys. Lett. 90, 121135 (2007); http://dx.doi.org/10.1063/1.2716972 (3 pages) | Cited 9 times

Online Publication Date: 23 March 2007

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The authors report on the fabrication and characterization of photonic crystal distributed feedback lasers, which are a generalization of distributed feedback and angled distributed feedback lasers. Spectral and spatial mode selection is provided by a two-dimensional, rectangular lattice of etched air holes that is tilted relatively to the cleaved facets. InGaAs/AlGaAs laser layers emitting around 1 μm were used for the fabrication of the devices. The laser emits at a single wavelength with a side mode suppression ratio of 50 dB. The emission is concentrated in a narrow far field, indicating that a coherent mode is formed over the entire width of the device.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
42.70.Qs Photonic bandgap materials

Ion beam irradiated channel waveguides in Er3+-doped tellurite glass

S. Berneschi, G. Nunzi Conti, I. Bányász, A. Watterich, N. Q. Khanh, M. Fried, F. Pászti, M. Brenci, S. Pelli, and G. C. Righini

Appl. Phys. Lett. 90, 121136 (2007); http://dx.doi.org/10.1063/1.2717085 (3 pages) | Cited 25 times

Online Publication Date: 23 March 2007

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Erbium-doped tellurite glasses are of great interest for the fabrication of active integrated circuits because of their unique properties in terms of bandwidth and rare earth solubility. The fabrication of multimode channel waveguides in a glass of this family, namely, a sodium-tungsten-tellurite glass, is demonstrated using a high-energy ion beam irradiation technique. Nitrogen ions with dose of 1.0×1016 ions/cm2 and 1.5 MeV energy were used for this aim. The waveguiding effect was investigated using the end-fire coupling technique.
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42.79.Gn Optical waveguides and couplers
42.70.Ce Glasses, quartz
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Extreme hydrogen plasma densities achieved in a linear plasma generator

G. J. van Rooij, V. P. Veremiyenko, W. J. Goedheer, B. de Groot, A. W. Kleyn, P. H. M. Smeets, T. W. Versloot, D. G. Whyte, R. Engeln, D. C. Schram, and N. J. Lopes Cardozo

Appl. Phys. Lett. 90, 121501 (2007); http://dx.doi.org/10.1063/1.2716208 (3 pages) | Cited 51 times

Online Publication Date: 23 March 2007

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A magnetized hydrogen plasma beam was generated with a cascaded arc, expanding in a vacuum vessel at an axial magnetic field of up to 1.6 T. Its characteristics were measured at a distance of 4 cm from the nozzle: up to a 2 cm beam diameter, 7.5×1020 m−3 electron density, ∼ 2 eV electron and ion temperatures, and 3.5 km/s axial plasma velocity. This gives a 2.6×1024 H+ m−2 s−1 peak ion flux density, which is unprecedented in linear plasma generators. The high efficiency of the source is obtained by the combined action of the magnetic field and an optimized nozzle geometry. This is interpreted as a cross-field return current that leads to power dissipation in the beam just outside the source.
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52.25.Xz Magnetized plasmas
52.50.Dg Plasma sources
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
52.25.Fi Transport properties

Modeling and simulation of the plasma absorption probe

M. Lapke, T. Mussenbrock, R. P. Brinkmann, C. Scharwitz, M. Böke, and J. Winter

Appl. Phys. Lett. 90, 121502 (2007); http://dx.doi.org/10.1063/1.2714202 (3 pages) | Cited 10 times

Online Publication Date: 23 March 2007

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The plasma absorption probe (PAP) was invented as an economical and robust diagnostic device to determine the electron density distribution in technical plasmas. It consists of a small antenna enclosed by a dielectric tube which is immersed in the plasma. A network analyzer feeds a rf signal to the antenna and displays the frequency dependence of the power absorption. From the absorption spectrum the value of the electron density is calculated. The original evaluation formula was based on the dispersion relation of plasma surface waves propagating along an infinite dielectric cylinder. In this letter the authors present the analysis of a less idealized configuration. The calculated spectra are in good qualitative agreement with their experimental counterparts, but differ considerably from those predicted by the surface wave ansatz. An evaluation scheme which takes our findings into account will improve the performance of the PAP technique further.
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52.70.Ds Electric and magnetic measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Fi Transport properties
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
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Effects of carbon nanotubes on electro-optical characteristics of liquid crystal cell driven by in-plane field

Sang Youn Jeon, Seung Hwan Shin, Seok Jin Jeong, Seung Hee Lee, Seok Ho Jeong, Young Hee Lee, Hyun Chul Choi, and Kyeong Jin Kim

Appl. Phys. Lett. 90, 121901 (2007); http://dx.doi.org/10.1063/1.2714311 (3 pages) | Cited 25 times

Online Publication Date: 19 March 2007

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Homogeneously aligned nematic liquid crystal (LC) cells doped with carbon nanotubes (CNTs) driven by an in-plane field were fabricated and their electro-optic characteristics were investigated. The effective cell retardation values showed no difference between doped and undoped LC cells in the absence of electric field. However, in the presence of electric field, it was smaller in the CNT-doped cell than in the undoped cell, resulting in the decrease of transmittance. Furthermore, the CNT-doped cell exhibited a slight increase in the driving voltage due to the increase of the twist elastic constant (K22) and the decrease in the decay response time due to the decrease in the rotational viscosity (γ) and γ/K22 compared to the undoped cell.
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42.70.Df Liquid crystals
78.20.Jq Electro-optical effects
61.72.up Other materials
62.10.+s Mechanical properties of liquids
66.20.-d Viscosity of liquids; diffusive momentum transport

Assessment of accumulated fatigue damage in solid plates using nonlinear Lamb wave approach

Mingxi Deng and Junfeng Pei

Appl. Phys. Lett. 90, 121902 (2007); http://dx.doi.org/10.1063/1.2714333 (3 pages) | Cited 26 times

Online Publication Date: 19 March 2007

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The feasibility of using the nonlinear effect of primary Lamb wave propagation for assessing accumulated fatigue damage in solid plates is theoretically analyzed. After the aluminum sheets are subjected to tension-tension fatigue loading for different numbers of loading cycles, they are subjected to ultrasonic tests near the driving frequency where Lamb waves have a strong nonlinearity. This is followed by the measurement of the amplitude-frequency curves for second harmonics of the considered Lamb waves. The experimental results show that the effect of second-harmonic generation by Lamb wave propagation is very sensitive to the accumulation of fatigue damage of solid plates.
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46.50.+a Fracture mechanics, fatigue and cracks
43.35.Pt Surface waves in solids and liquids
43.25.-x Nonlinear acoustics
68.35.Iv Acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Symmetry properties and anisotropic excitonic response for GaN films grown on semipolar (11−22)-, (10−11)-, and (10−13)-oriented GaN substrates

Bernard Gil

Appl. Phys. Lett. 90, 121903 (2007); http://dx.doi.org/10.1063/1.2715003 (3 pages) | Cited 6 times

Online Publication Date: 19 March 2007

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The author analyzes the optical properties of GaN homoepitaxies grown on semipolar (11−2x)- and (10−1x)-oriented GaN substrates. He works here in the specific cases of (11−22)-, (10−11)-, and (10−13)-orientations which currently deserve intense experimental activity. The author finds the optical anisotropy of the GaN films to be strictly ruled by the angle between the growth plane and the ⟨001⟩ direction of the GaN material.
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78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena

Heteroepitaxial growth of sixfold symmetric osmium on Si (111) and Si (100)

Tai-Yen Peng, C. K. Lo, Y. D. Yao, and San-Yuan Chen

Appl. Phys. Lett. 90, 121904 (2007); http://dx.doi.org/10.1063/1.2711658 (3 pages) | Cited 3 times

Online Publication Date: 19 March 2007

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Growing sixfold symmetric osmium (Os) epitaxial films with suitable buffer layers was developed. Using a Cu buffer layer, the lattice mismatch between Os (0002) and Si (100) was significantly reduced from >30% to ∼ 7% to grow Os films with twin relationships and weak sixfold symmetries. On the other hand, the Cu/Au buffer layer was selected to form a fcc (111) surface mesh on H–Si (111)-1×1, and therefore sixfold symmetric Os films were grown due to the lower lattice mismatch. Such growth properties may be applied in the high density magnetic random access memory manufacturing processes to connect the magnetic tunnel junction growth and Cu metal line directly.
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68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.Gy Mechanical properties; surface strains
68.60.Bs Mechanical and acoustical properties
61.72.Mm Grain and twin boundaries

Anomalous thermal stability of cubic tin confined in a nanotube

B. Wang, G. Ouyang, Y. H. Yang, and G. W. Yang

Appl. Phys. Lett. 90, 121905 (2007); http://dx.doi.org/10.1063/1.2715136 (3 pages) | Cited 5 times

Online Publication Date: 19 March 2007

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In situ observations of transmission electron microscopy have indicated that the cubic Sn phase confined in a nanotube has extreme stability even when the temperature is more than 700 °C, significantly higher than the melting point (231.9 °C) of tin. A thermodynamic model was established to pursue the physical origins of the anomalous stability of the confined cubic Sn phase. It was found that the epitaxial interface confinement of SnO2/Sn and the difference of thermal expansion between the core and shell play crucial roles in the unusual stability of the cubic Sn at high temperature.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
61.46.Fg Nanotubes

Schottky ultraviolet photodiode using a ZnO hydrothermally grown single crystal substrate

Haruyuki Endo, Mayo Sugibuchi, Kousuke Takahashi, Shunsuke Goto, Shigeaki Sugimura, Kazuhiro Hane, and Yasube Kashiwaba

Appl. Phys. Lett. 90, 121906 (2007); http://dx.doi.org/10.1063/1.2715100 (3 pages) | Cited 32 times

Online Publication Date: 20 March 2007

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A Schottky ultraviolet photodiode using a (0001) ZnO single crystal grown by the hydrothermal growth method is reported. The photodiode consisted of a semitransparent Pt film for the Schottky electrode and an Al thin film for the Ohmic electrode. The photodiode had polarity dependences on current-voltage characteristics and on responsivity. In the case of the Schottky electrode on the zinc surface, the responsivity was 0.185 A/W at a wavelength of 365 nm. On the other hand, the responsivity was 0.09 A/W for an oxygen surface. The results are attributed to the polarity dependences of surface chemical reactivity and the surface state density on ZnO surfaces.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Kk Junction diodes
85.60.Gz Photodetectors (including infrared and CCD detectors)

Microstructure analysis of c-axis oriented aluminum nitride thin films by high-resolution transmission electron microscopy

Z. Q. Yao, Q. Ye, Y. Q. Li, Y. S. Zou, W. J. Zhang, and S. T. Lee

Appl. Phys. Lett. 90, 121907 (2007); http://dx.doi.org/10.1063/1.2715173 (3 pages) | Cited 7 times

Online Publication Date: 20 March 2007

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The microstructure, in particular, the surface and interface regions, of the c-axis orientated AlN films deposited on Si (100) substrates was studied. The films showed an evolutionary columnar growth process. In contrast to the previous reports, high-resolution transmission electron microscopy revealed that the AlN films grew directly on substrates without an amorphous interlayer, despite the large lattice mismatch between AlN and Si. The occurrence of misoriented and/or amorphous top layer suggested a subsurface growth/relaxation process of the AlN films by reactive sputtering.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering

Wafer-level microelectromechanical system structural material test by electrical signal before pull-in

Yuh-Chung Hu and Po-Yuan Huang

Appl. Phys. Lett. 90, 121908 (2007); http://dx.doi.org/10.1063/1.2714998 (3 pages) | Cited 1 time

Online Publication Date: 21 March 2007

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The letter develops a wafer-level testing method to examine Young’s modulus and residual stress of structural material of capacitive microdevice by measuring the pre-pull-in capacitance variation of the microtest beam made of the material to be tested. The required instrument is only a precision LCR meter. The extracted Young’s moduli and residual stresses of demonstrated samples agree very well with the experimental measurement. The present method is expected to be applicable to the wafer-level testing in microdevice manufacture and compatible with the wafer-level testing in integrated circuit industry, since the test and pickup signals are both electrical.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.70.Bt Mechanical testing, impact tests, static and dynamic loads

Phase transition of ultrathin AlN interlayer at AlGaN/GaN interface

Duanjun Cai and Junyong Kang

Appl. Phys. Lett. 90, 121909 (2007); http://dx.doi.org/10.1063/1.2711379 (3 pages)

Online Publication Date: 21 March 2007

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The authors report the wurtizite to zinc-blende phase transition of ultrathin AlN interlayer at the interface of AlGaN/GaN. The shape transformation of the pinhole from hexagon to dodecagon exhibits the structural transition of the interfacial layer, where exists an AlN segregation interlayer. By transmission electron diffraction, the structure of AlN interlayer is determined to be zinc blende. Ab initio simulations demonstrate that the epitaxial strain favors the formation of the high Al segregation and the phase transition.
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64.70.K- Solid-solid transitions
68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology
64.75.-g Phase equilibria

Effect of ionization rates on dynamic recovery processes during electron-beam irradiation of 6H-SiC

In-Tae Bae, William J. Weber, Manabu Ishimaru, and Yoshihiko Hirotsu

Appl. Phys. Lett. 90, 121910 (2007); http://dx.doi.org/10.1063/1.2715135 (3 pages) | Cited 6 times

Online Publication Date: 21 March 2007

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The authors have investigated the effects of 200 and 300 keV electron-beam irradiations on amorphization in 6H-SiC at 100 and 295 K. Amorphization is induced by the accumulation of defects produced by direct atomic displacements. Dynamic recovery of these defects during irradiation, due to temperature increases and ionization effects, results in increases in the amorphization dose. By comparing with previous data for 2 MeV electrons and 1.5 MeV Xe ions, the results demonstrate that ionization-enhanced recovery in 6H-SiC dramatically increases above an ionization rate threshold.
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61.82.Fk Semiconductors
61.80.Fe Electron and positron radiation effects
61.43.Dq Amorphous semiconductors, metals, and alloys

Role of gross well-width fluctuations in bright, green-emitting single InGaN/GaN quantum well structures

Nicole K. van der Laak, Rachel A. Oliver, Menno J. Kappers, and Colin J. Humphreys

Appl. Phys. Lett. 90, 121911 (2007); http://dx.doi.org/10.1063/1.2715166 (3 pages) | Cited 25 times

Online Publication Date: 21 March 2007

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Gross well-width fluctuations have been observed by transmission electron microscopy (TEM) in single InGaN/GaN quantum wells (QWs) grown by metal-organic vapor phase epitaxy. Similar thickness variations are observed in commercial, green InGaN/GaN multi-QW light emitting diodes. Atomic force microscopy studies of equivalent epilayers suggest that these fluctuations arise from a network of interlinking InGaN strips, which are found (using TEM) to be indium rich at their centers. Plan-view TEM indicates that 90±8% of all threading dislocations (TDs) intersect the QW plane between the InGaN strips. Excitons may be localized at the strips’ centers, preventing nonradiative recombination at TDs.
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68.65.Fg Quantum wells
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
71.35.-y Excitons and related phenomena

Modified efficient cluster packing model for calculating alloy compositions with high glass forming ability

A. P. Wang, J. Q. Wang, and E. Ma

Appl. Phys. Lett. 90, 121912 (2007); http://dx.doi.org/10.1063/1.2715172 (3 pages) | Cited 4 times

Online Publication Date: 21 March 2007

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The efficient cluster packing model for bulk metallic glasses (BMGs) has been modified and extended to allow quantitative predictions of alloy compositions with high glass forming ability. The compositions calculated using this simple method compare favorably with the vast majority of the BMGs discovered in recent years. In addition, a Hf-based BMG has been obtained at the predicted composition.
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61.43.Fs Glasses
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
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