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30 May 2005

Volume 86, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 223902 (2005); http://dx.doi.org/10.1063/1.1938253 (3 pages)

Philip J. Lee, Paul J. Hung, Robin Shaw, Lily Jan, and Luke P. Lee
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GaN-based light-emitting diodes with indium tin oxide texturing window layers using natural lithography

R. H. Horng, C. C. Yang, J. Y. Wu, S. H. Huang, C. E. Lee, and D. S. Wuu

Appl. Phys. Lett. 86, 221101 (2005); http://dx.doi.org/10.1063/1.1940723 (3 pages) | Cited 57 times

Online Publication Date: 24 May 2005

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There is a significant gap between the internal and external efficiencies of conventional GaN light-emitting diodes (LEDs). The reason for this shortfall is the narrow escape cone for light in high refractive index semiconductors. In this letter, the p-side-up GaN/sapphire LEDs with surface textured indium tin oxide (ITO) widow layers were investigated using natural lithography with polystyrene spheres as the etching mask. Under optimum etching conditions, the surface roughness of the ITO film can reach 140 nm while the polystyrene sphere on the textured ITO surface is maintained at about 250–300 nm in diameter. The output power of the ITO/GaN LED with and without surface texturing is 10.9, and 8.5 mW at 20 mA, respectively. The LEDs fabricated using the surface-textured ITO produced an output power that exceeded that of the planar-surface LED by about 28% at 20 mA.
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85.60.Jb Light-emitting devices
81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning

Amplified spontaneous emission in an organic semiconductor multilayer waveguide structure including a highly conductive transparent electrode

M. Reufer, J. Feldmann, P. Rudati, A. Ruhl, D. Müller, K. Meerholz, C. Karnutsch, M. Gerken, and U. Lemmer

Appl. Phys. Lett. 86, 221102 (2005); http://dx.doi.org/10.1063/1.1938001 (3 pages) | Cited 19 times

Online Publication Date: 24 May 2005

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We demonstrate that the amplified spontaneous emission (ASE) threshold in multilayer waveguide structures suitable for the use in future organic injection lasers can be drastically reduced by inserting a crosslinked hole transport layer (HTL) between a highly conductive indium tin oxide (ITO) electrode and the polymer emission layer. While no ASE is observed when the active layer material is directly spincoated onto the ITO electrode, it can be completely restored upon insertion of a 300-nm-thick HTL. This observation is attributed to reduced attenuation of the waveguided mode enabling the ASE process and is theoretically confirmed by calculations of the mode intensity fraction propagating in the absorptive ITO electrode.
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68.65.Ac Multilayers
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
78.45.+h Stimulated emission
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Stability of phase-modulated quantum key distribution systems

Zheng-Fu Han, Xiao-Fan Mo, You-Zhen Gui, and Guang-Can Guo

Appl. Phys. Lett. 86, 221103 (2005); http://dx.doi.org/10.1063/1.1931824 (3 pages) | Cited 11 times

Online Publication Date: 24 May 2005

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The stability of double Mach–Zehnder implementation has been investigated in experiment, which is important for practical quantum key distribution systems. The results of experiment show that the random fluctuation of interference visibility comes from polarization disturbance, especially from that of transmission fiber. A theoretical model is built and a necessary condition is given for intrinsic-stabilization unidirectional quantum key distribution system.
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03.67.Dd Quantum cryptography and communication security
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Integrated chirp compensation in a monolithic passively mode-locked semiconductor diode laser

Michael B. Flynn, Liam O’Faolain, and Thomas F. Krauss

Appl. Phys. Lett. 86, 221104 (2005); http://dx.doi.org/10.1063/1.1940728 (2 pages) | Cited 3 times

Online Publication Date: 25 May 2005

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We present traveling wave numerical simulations of passively mode-locked diode lasers that incorporate chirp compensation monolithically using a Fabry–Pérot interferometer, which provides a negative group delay. Numerical results show pulse compression of up to 65%. Time-frequency domain study of the pulses reveal a significant reduction in chirp across the pulse. Limitations of this simple linear chirp compensation scheme are examined.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
85.60.Bt Optoelectronic device characterization, design, and modeling
07.60.Ly Interferometers

Mask-free photolithographic exposure using a matrix-addressable micropixellated AlInGaN ultraviolet light-emitting diode

C. W. Jeon, E. Gu, and M. D. Dawson

Appl. Phys. Lett. 86, 221105 (2005); http://dx.doi.org/10.1063/1.1942636 (3 pages) | Cited 20 times

Online Publication Date: 25 May 2005

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We report the integration of a UV-curable polymer microlens array onto a matrix-addressable, 368-nm-wavelength, light-emitting diode device containing 64×64 micropixel elements. The geometrical and optical parameters of the microlenses were carefully chosen to allow the highly divergent emission from each micropixel to be collimated into a narrow beam of about 8-μm diam, over a distance of more than 500 μm. This device is demonstrated as a photolithographic exposure tool, where the pattern-programmable array plays the role both of light source and photomask. A simple pattern comprised of two disks having 16-μm diam and 30-μm spacing was transferred into an i-line photoresist.
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85.60.Jb Light-emitting devices
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.65.Cf Surface cleaning, etching, patterning
42.79.Bh Lenses, prisms and mirrors
42.70.Jk Polymers and organics
42.72.Bj Visible and ultraviolet sources

Microfabricated SrTiO3 ridge waveguides

M. Gaidi, L. Stafford, J. Margot, M. Chaker, R. Morandotti, and M. Kulishov

Appl. Phys. Lett. 86, 221106 (2005); http://dx.doi.org/10.1063/1.1942634 (3 pages) | Cited 5 times

Online Publication Date: 26 May 2005

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We report the microfabrication and characterization of SrTiO3/SiO2/Si ridge waveguides. SrTiO3 films are very attractive for optical integrated systems as they present a high transparency in the visible and infrared wavelength range as well as a relatively high refractive index. In this work, SrTiO3 films were grown by means of a reactive pulsed-laser-deposition technique and patterned using UV photolithography and high-density plasma etching. Propagation and loss characteristics at the telecommunication wavelength of 1.55 μm were investigated using top-view scattering and Fabry-Perot resonance methods. For specific ridge widths, we obtained single-mode propagation with relatively low losses ( ∼ 1.5 dB/cm), thereby demonstrating the strong potential of SrTiO3 films for guided-wave components for advanced optical integrated systems.
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42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Wc Optical coatings
81.15.Fg Pulsed laser ablation deposition
85.40.Hp Lithography, masks and pattern transfer

Transmission terahertz waveguide-based imaging below the diffraction limit

M. M. Awad and R. A. Cheville

Appl. Phys. Lett. 86, 221107 (2005); http://dx.doi.org/10.1063/1.1942637 (3 pages) | Cited 24 times

Online Publication Date: 26 May 2005

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Using a terahertz line source from a near dispersion-free parallel plate waveguide, we demonstrate broad bandwidth imaging at terahertz frequencies with subwavelength image resolution. Terahertz radiation is coupled into a parallel plate waveguide with a 100 μm plate spacing, which serves as the imaging aperture. The image data are collected as projections and the final image is reconstructed using the filtered back-projection algorithm, similar to that in x-ray computed tomography. Images taken using a waveguide-based line source demonstrate higher resolution than can be achieved using a confocal cylindrical lens setup.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
42.79.Gn Optical waveguides and couplers
42.30.Wb Image reconstruction; tomography

Reverse-bias electroluminescence imaging to diagnose failures of vertical-cavity surface-emitting lasers

D. K. McElfresh and D. Vacar

Appl. Phys. Lett. 86, 221108 (2005); http://dx.doi.org/10.1063/1.1943496 (3 pages) | Cited 2 times

Online Publication Date: 27 May 2005

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The charge flowing through the junction of vertical-cavity surface-emitting lasers (VCSELs) under reverse-bias gives rise to electroluminescence (EL) when breakdown conditions are satisfied. We collected the reverse-bias EL of VCSEL devices that had been subjected to accelerated stress. We observed distinctly different spatial distributions of the reverse-bias EL: for survivor (nondegraded) devices the breakdown current appears to be confined to one well-defined filament while for dark (degraded) VCSELs the reverse-bias EL pattern is a disordered network of filaments. We show that the line dislocation network that renders the VCSELs dark is directly imaged as the spatial distribution of the reverse-bias EL.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Phospho-tellurite glasses containing heavy metal oxides for ultrabroad band fiber Raman amplifiers

G. Senthil Murugan, Takenobu Suzuki, and Yasutake Ohishi

Appl. Phys. Lett. 86, 221109 (2005); http://dx.doi.org/10.1063/1.1944225 (3 pages) | Cited 11 times

Online Publication Date: 27 May 2005

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Multicomponent phospho-tellurite glasses containing heavy metal oxides and alkaline earth oxides have been fabricated. These glasses have thermal stabilities as high as 224 °C, which make them suitable for various fiber devices applications. The Raman intensities and cross sections of these glasses are compared relative to silica. These glasses show superior relative Raman cross sections than silica and conventional tellurite glasses. The presence of heavy metal oxides and alkaline earth oxides makes the Raman bands due to TeO2 and P2O5 continuous and one such glass has continuous Raman bandwidths exceeding 700 cm−1. Thus, these glasses could be potential candidates for ultrawide band fiber Raman amplifiers.
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42.70.Ce Glasses, quartz
81.05.Kf Glasses (including metallic glasses)
78.30.Hv Other nonmetallic inorganics
42.55.Wd Fiber lasers
42.55.Ye Raman lasers
42.60.By Design of specific laser systems
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Tunable electrochromic photonic crystals

Su-Lan Kuai, Georges Bader, and P. V. Ashrit

Appl. Phys. Lett. 86, 221110 (2005); http://dx.doi.org/10.1063/1.1929079 (3 pages) | Cited 34 times

Online Publication Date: 27 May 2005

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Photonic crystals based on the electrochromic phenomenon have been fabricated and proposed for band gap tuning. Electrochromic tungsten trioxide (WO3) inverse opals have been fabricated by polystyrene colloidal crystal templating. The WO3 matrix was obtained through a dip-infiltrating sol-gel process, with subsequent removal of the polymer microspheres by calcination. Scanning electron micrographs confirm the ordering of the hexagonal macroporous structure. The reflection spectra show two pronounced Bragg diffraction peaks. By inserting lithium into the crystals, the first reflection peak shifts gradually toward shorter wavelength for 36 nm, while the second reflection peak shifts toward longer wavelength for about 28 nm. This should be of great interest for photonic device applications.
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42.70.Qs Photonic bandgap materials
81.40.Gh Other heat and thermomechanical treatments
42.86.+b Optical workshop techniques
61.43.Gt Powders, porous materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Thermo-optic photonic crystal light modulator

Mark T. Tinker and Jeong-Bong Lee

Appl. Phys. Lett. 86, 221111 (2005); http://dx.doi.org/10.1063/1.1944212 (3 pages) | Cited 11 times

Online Publication Date: 27 May 2005

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A device concept is proposed for modulating light in silicon-based photonic crystal devices by using highly localized high-temperature modulation of a compact device to vary the position of the cutoff frequency in a photonic crystal waveguide and modulate light. The position of the cutoff frequency can be varied by up to 60 nm at the telecommunication wavelength of 1550 nm by locally increasing the temperature of the device. Modulators of a few to several micrometers in width can be designed that can modulate light with extinction ratios up to 50 dB and low insertion loss.
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42.79.Hp Optical processors, correlators, and modulators
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
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Nanoporous alumina as a dielectric for microcavity plasma devices: Multilayer Al/Al2O3 structures

S.-J. Park, K. S. Kim, and J. G. Eden

Appl. Phys. Lett. 86, 221501 (2005); http://dx.doi.org/10.1063/1.1923747 (3 pages) | Cited 24 times

Online Publication Date: 24 May 2005

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Nanostructured Al2O3 films with mean pore diameters of 20 nm, 5–30 μm in thickness, and grown onto Al foil by a multiple step electrochemical process, provide a dielectric having superior properties for microplasma devices and arrays. Multilayer Al/nanoporous Al2O3 structures with a 100–300 μm diameter (dia.) cylindrical microcavity and an overall thickness of ∼ 200 μm are robust and operate in the abnormal glow mode for Ne or Ar/2–5% N2 mixture gas pressures (300 K) of 500–700 Torr. When driven with a sinusoidal ac waveform at frequencies of 5–20 kHz, small arrays (3×3→10×10) of 100 μm dia. devices operate in Ne at rms voltages and currents of ∼ 160–270 V and 0.4–4.5 mA, respectively. Arrays as large as 10×10 have been fabricated to date and generate azimuthally uniform discharges in each pixel without the need for external ballast. For an rms voltage of ∼ 275 V, 5×5 arrays of 100 μm dia. devices produce a luminance of 2700 cd m−2 in 600 Torr of Ne for a sinusoidal ac excitation frequency of 20 kHz.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
81.05.Rm Porous materials; granular materials
78.66.Nk Insulators
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
73.61.Ng Insulators
61.46.-w Structure of nanoscale materials
52.75.-d Plasma devices
52.80.Hc Glow; corona
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Pressure-induced transient structural change of liquid germanium induced by high-energy picosecond laser pulses

N. Chaoui, J. Siegel, S. M. Wiggins, and J. Solis

Appl. Phys. Lett. 86, 221901 (2005); http://dx.doi.org/10.1063/1.1940117 (3 pages) | Cited 2 times

Online Publication Date: 24 May 2005

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The temporal evolution of the reflectivity of germanium at 514 nm upon irradiation with single high-energy picosecond laser pulses has been measured using a streak camera. It is found that, for a well-defined high fluence range, the reflectivity of the laser-induced molten phase attains a value of 0.85, considerably above the value reported for liquid Ge in thermal equilibrium (0.75). This behavior is consistent with a strong densification of the liquid phase remaining after the explosive vaporization of a thin surface layer. Within the specified fluence interval, this anomalously high reflectivity state is independent of the fluence and lasts tens of nanoseconds. Both characteristics point to the presence of a pressure-induced transient structural change in liquid germanium.
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62.50.-p High-pressure effects in solids and liquids
78.47.-p Spectroscopy of solid state dynamics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
64.70.F- Liquid-vapor transitions
61.25.-f Studies of specific liquid structures

Ion damage effects from negative deflector plate voltages during the plasma-assisted molecular-beam epitaxy growth of dilute nitrides

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

Appl. Phys. Lett. 86, 221902 (2005); http://dx.doi.org/10.1063/1.1940126 (3 pages) | Cited 5 times

Online Publication Date: 24 May 2005

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We studied the effects of ion damage on the optical properties of dilute nitrides grown by plasma-assisted molecular-beam epitaxy. A dual-grid retarding field ion energy analyzer was used to measure the ion flux and ion energy distribution at the substrate position from an Applied-EPI UniBuilb™ rf plasma cell. These changes were measured as the negative deflector plate voltage varied from 0 to −800 V. The largest ion flux resulted with a −100 V setting, while the greatest ion energies occurred with −200 V. Deflector plate voltages more negative than −300 V resulted in a significant reduction in both the ion flux and ion energy. The damage caused by these ions was determined by measuring the pre- and postanneal photoluminescence properties of Ga0.8In0.2N0.01As0.99 quantum wells. Comparable optical properties were possible with various combinations of ion fluxes and ion energies, which demonstrate how the ion flux and ion energy each impart an individual effect on the sample’s optical properties. An awareness of these effects is crucial because the optical properties of dilute nitrides grown with an improper deflector plate voltage setting can lead to a greater degree of ion damage to the sample.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Fg Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
52.77.Dq Plasma-based ion implantation and deposition

Critical precipitate size revisited and implications for oxygen precipitation in silicon

Jan Vanhellemont, Olivier De Gryse, and Paul Clauws

Appl. Phys. Lett. 86, 221903 (2005); http://dx.doi.org/10.1063/1.1940140 (3 pages) | Cited 3 times

Online Publication Date: 24 May 2005

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A generalized expression is derived describing the impact of intrinsic point defects and strain on the critical size of spheroidal incoherent precipitates. An important phenomenon that has been neglected so far is the incorporation of intrinsic point defects of the host matrix in the precipitate itself. It is shown that this can have an important impact both on the critical precipitate size, on the amount of emitted intrinsic point defects, and on the precipitated phase itself. The theoretical results are illustrated for the case of oxygen precipitation in silicon.
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81.30.Mh Solid-phase precipitation
61.72.J- Point defects and defect clusters

Phonons in strained In1−xGaxAs/InP epilayers characterized by infrared reflectance

G. Yu, N. L. Rowell, D. J. Lockwood, and P. J. Poole

Appl. Phys. Lett. 86, 221904 (2005); http://dx.doi.org/10.1063/1.1940732 (3 pages) | Cited 5 times

Online Publication Date: 24 May 2005

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Strained In1−xGaxAs epilayers over a wide range of x values from 0.252 to 0.762 have been grown by chemical beam epitaxy on heavily doped InP(100) substrates. The infrared p-polarized reflectivity of these samples has been measured and the first derivative of the reflectance has been analyzed using a specially developed fitting technique. Expressions for the variation of the phonon frequencies with Ga fraction for the InAs-like and GaAs-like modes have been obtained. The present results substantially improve on earlier results obtained from epilayers on semi-insulating substrates having a narrower concentration range around x = 0.468 where In1−xGaxAs is lattice matched to InP.
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81.05.Ea III-V semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors

Spin-selective optical absorption of singly charged excitons in a quantum dot

Alexander Högele, Martin Kroner, Stefan Seidl, Khaled Karrai, Mete Atatüre, Jan Dreiser, Atac Imamoğlu, Richard J. Warburton, Antonio Badolato, Brian D. Gerardot, and Pierre M. Petroff

Appl. Phys. Lett. 86, 221905 (2005); http://dx.doi.org/10.1063/1.1940733 (3 pages) | Cited 25 times

Online Publication Date: 24 May 2005

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We report high resolution laser absorption spectroscopy of a single InGaAs/GaAs self-assembled quantum dot embedded in a field-effect structure. We show experimentally that the interband optical absorption to the lower Zeeman branch of the singly charged exciton is strongly inhibited due to spin (Pauli) blockade of the optical transition. At high magnetic fields the optical absorption to the upper Zeeman branch dominates the absorption spectrum. We find, however, that the spin blockade is not complete and a 10% leakage remains at high magnetic fields. Applying a gate voltage to empty the dot of its resident electron turns the spin blockade off. This effect is observed at 1.5 K and up to 9 T.
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81.05.Ea III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.66.Fd III-V semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Ls Magneto-optical effects

Amorphous carbon film growth on Si: Correlation between stress and generation of defects into the substrate

R. S. Brusa, C. Macchi, S. Mariazzi, G. P. Karwasz, N. Laidani, R. Bartali, and M. Anderle

Appl. Phys. Lett. 86, 221906 (2005); http://dx.doi.org/10.1063/1.1940738 (3 pages) | Cited 3 times

Online Publication Date: 24 May 2005

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Amorphous carbon films of several thicknesses were prepared by graphite sputtering on crystalline silicon substrate. The samples were depth profiled with positron annihilation spectroscopy for open-volume measurements and characterized for their residual internal stress. It was found that after film growth the substrate presents vacancy-like defects decorated by oxygen in a layer extending in the substrate by several tens of nanometers beyond the film/Si interface. The width of the defected layer and the decoration of vacancy-like defects are directly and inversely proportional to the measured intensity of the residual stress, respectively. These findings indicate the existence of a relaxation mechanism of the stress in the films that involves deeply the substrate. The decorated vacancy-like defects are suggested to be bounded to dislocations induced in the substrate by the stress relaxation.
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81.05.U- Carbon/carbon-based materials
68.60.Bs Mechanical and acoustical properties
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
78.70.Bj Positron annihilation
61.72.J- Point defects and defect clusters

Photoluminescence characterization of excitonic centers in ZnO epitaxial films

M. Watanabe, M. Sakai, H. Shibata, H. Tampo, P. Fons, K. Iwata, A. Yamada, K. Matsubara, K. Sakurai, S. Ishizuka, S. Niki, K. Nakahara, and H. Takasu

Appl. Phys. Lett. 86, 221907 (2005); http://dx.doi.org/10.1063/1.1940730 (3 pages) | Cited 9 times

Online Publication Date: 24 May 2005

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Photoluminescence properties of nominally undoped ZnO thin films grown by radical-source molecular-beam epitaxy have been investigated as a function of (i) sample growth conditions, (ii) excitation laser power density, and (iii) measurement temperatures. Altogether four excitonic emission peaks were observed at photon energy of 3.3646, 3.3606, 3.3572, and 3.3331 eV, which are tentatively denoted as emission peaks A, D, F, and G, respectively. We have classified the defect types responsible for the emission peaks into the following two groups; (i) D and F, whose responsible defect types are suggested to be residual impurities such as aluminum and indium, respectively, and (ii) A and G, whose responsible defect types are suggested to be intrinsic defects such as oxygen vacancies, interstitial zinc, and extended structural defects particularly for G.
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81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
71.35.-y Excitons and related phenomena
61.72.Nn Stacking faults and other planar or extended defects
61.72.J- Point defects and defect clusters

Proton irradiation effect on single-wall carbon nanotubes in a poly(3-octylthiophene) matrix

P. P. Neupane, M. O. Manasreh, B. D. Weaver, R. P. Rafaelle, and B. J. Landi

Appl. Phys. Lett. 86, 221908 (2005); http://dx.doi.org/10.1063/1.1940721 (3 pages) | Cited 6 times

Online Publication Date: 24 May 2005

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Proton irradiation effects on interband transitions in single-wall carbon nanotubes matrixed in poly(3-octylthiophene) were investigated. The interband transitions were measured using an optical absorption technique. Two interband transitions were observed, at 0.71 and 1.28 eV in a sample that was subject to 2 MeV proton irradiation to fluences ranging between 5.0×1010 cm−2 and 5.6×1015 cm−2. The optical absorption spectra were collected after cooling the sample to 10 K. The total integrated areas of the two transitions were monitored as a function of proton fluence. The results indicate that proton irradiation to fluences as high as 5.6×1015 cm−2 has little effect on the interband transitions in carbon nanotubes. However, small radiation-related degradation has been observed as judged by the broadening of the interband transition spectra and by the reduction of the radial breathing mode intensity observed by Raman scattering.
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81.07.De Nanotubes
81.05.Qk Reinforced polymers and polymer-based composites
61.80.Jh Ion radiation effects
61.82.Rx Nanocrystalline materials
78.30.-j Infrared and Raman spectra
78.67.Ch Nanotubes

CdTe photoluminescence: Comparison of solar-cell material with surface-modified single crystals

C. R. Corwine, J. R. Sites, T. A. Gessert, W. K. Metzger, P. Dippo, Jingbo Li, A. Duda, and G. Teeter

Appl. Phys. Lett. 86, 221909 (2005); http://dx.doi.org/10.1063/1.1935752 (3 pages) | Cited 4 times

Online Publication Date: 24 May 2005

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Low-temperature photoluminescence (PL) is used to study defect evolution during Cu diffusion into single-crystal CdTe under various atmospheres. PL reveals a zero-order phonon peak at 1.456 eV when Cu-coated CdTe is annealed at 400 °C in an oxidizing atmosphere, but not under other tested conditions. A similar peak is seen in polycrystalline thin-film CdTe samples, which are known to contain copper and oxygen impurities. First-principles band structure calculations determined the likely defect assignment as a transition between a Cui–OTe donor complex and the valence band.
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81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
78.66.Hf II-VI semiconductors
71.15.-m Methods of electronic structure calculations
61.72.Cc Kinetics of defect formation and annealing
66.30.J- Diffusion of impurities
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.65.Mq Oxidation
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
84.60.Jt Photoelectric conversion

Aging effect and origin of deep-level emission in ZnO thin film deposited by pulsed laser deposition

F. K. Shan, G. X. Liu, W. J. Lee, G. H. Lee, I. S. Kim, and B. C. Shin

Appl. Phys. Lett. 86, 221910 (2005); http://dx.doi.org/10.1063/1.1939078 (3 pages) | Cited 59 times

Online Publication Date: 24 May 2005

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ZnO thin films were deposited on sapphire substrates at 400 °C in the pulsed laser deposition (PLD) system. Those thin films showed two emission peaks. One was near band edge emission at around 379 nm; the other was deep-level (DL) emission at around 510 nm. The aging effect on photoluminescence (PL) of the thin film was observed. It was found that the DL emission decreased with time. Post-annealing processes were carried out to find the origin of the DL emission. The thin films were annealed at 800 °C in N2 or O2 ambient gas in a rapid thermal annealing system. An atomic force microscope was used to investigate the surface morphologies of the thin films. The surface roughness of annealed thin film was much smaller than that of the as-deposited one. The transmittance of the annealed thin film decreased much compared with that of the as-deposited thin film. The DL emission of the thin film annealed in N2 increased, and the DL emission of thin film annealed in O2 decreased. The oxygen vacancies instead of zinc interstitials were the main reason for DL emission in ZnO thin films deposited by PLD.
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
68.37.Ps Atomic force microscopy (AFM)
71.55.Gs II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.J- Point defects and defect clusters

Compositional stability of hafnium aluminates thin films deposited on Si by atomic layer deposition

C. Driemeier, K. P. Bastos, L. Miotti, I. J. R. Baumvol, N. V. Nguyen, S. Sayan, and C. Krug

Appl. Phys. Lett. 86, 221911 (2005); http://dx.doi.org/10.1063/1.1940130 (3 pages) | Cited 6 times

Online Publication Date: 24 May 2005

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We have used nuclear reaction analyses and Rutherford backscattering spectrometry to investigate quantitatively the compositional stability of hafnium aluminate thin films deposited on Si(001) by atomic layer deposition using HfCl4/H2O and Al(CH3)3/H2O precursors. It was found that increasing Al/Hf deposition cycles ratio leads to increasing oxygen deficiency in the as-deposited films as well as to increasing metal losses (up to ∼ 15%) from the films after rapid thermal annealing at 1000 °C. Furthermore, isotopic substitution experiments, showed that incorporation of oxygen from the gas phase is eased in the cases where deposition conditions failed to supply enough oxygen to complete oxides stoichiometry.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.22.Gm Dielectric loss and relaxation
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.Cc Kinetics of defect formation and annealing
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Gold film with gold nitride—A conductor but harder than gold

L. Šiller, N. Peltekis, S. Krishnamurthy, Y. Chao, S. J. Bull, and M. R. C. Hunt

Appl. Phys. Lett. 86, 221912 (2005); http://dx.doi.org/10.1063/1.1941471 (3 pages) | Cited 11 times

Online Publication Date: 24 May 2005

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The formation of surface nitrides on gold films is a particularly attractive proposition, addressing the need to produce harder, but still conductive, gold coatings which reduce wear but avoid the pollution associated with conventional additives. Here we report production of large area gold nitride films on silicon substrates, using reactive ion sputtering and plasma etching, without the need for ultrahigh vacuum. Nanoindentation data show that gold nitride films have a hardness ∼ 50% greater than that of pure gold. These results are important for large-scale applications of gold nitride in coatings and electronics.
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62.20.Qp Friction, tribology, and hardness
81.05.Bx Metals, semimetals, and alloys
81.65.−b
79.60.−i
79.60.Dp Adsorbed layers and thin films
81.15.Cd Deposition by sputtering
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Optimized energy window of He beams for accurate determination of depth in channeling Rutherford backscattering spectrometry

Lin Shao, Y. Q. Wang, X. Zhang, C. J. Wetteland, M. Nastasi, P. E. Thompson, and J. W. Mayer

Appl. Phys. Lett. 86, 221913 (2005); http://dx.doi.org/10.1063/1.1941454 (3 pages) | Cited 2 times

Online Publication Date: 24 May 2005

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We propose a method to improve accurate determination of damage/impurity depth profiles by channeling Rutherford backscattering by using math beams in an energy window of 400–800 keV. This is based on the study of the stopping power of math ions as a function of incident energy along the Si 〈100〉 axis, which shows that the channeling stopping power within the above energy window is close to the random stopping power. Experiments on 100 nm deep Sb-doped Si superlattices show that the approach significantly reduces the error in determining the depth location of Sb, for example, from 8% by using 2-MeV math to 1% by using 600-keV math ions.
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61.85.+p Channeling phenomena (blocking, energy loss, etc.)
34.50.Bw Energy loss and stopping power
34.50.−s
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