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20 Jul 2009

Volume 95, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 033502 (2009); http://dx.doi.org/10.1063/1.3178556 (3 pages)

Akihito Ikedo, Takahiro Kawashima, Takeshi Kawano, and Makoto Ishida
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A plasma microlens for ultrashort high power lasers

Yiftach Katzir, Shmuel Eisenmann, Yair Ferber, Arie Zigler, and Richard F. Hubbard

Appl. Phys. Lett. 95, 031101 (2009); http://dx.doi.org/10.1063/1.3184788 (3 pages) | Cited 3 times

Online Publication Date: 20 July 2009

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We present a technique for generation of miniature plasma lens system that can be used for focusing and collimating a high intensity femtosecond laser pulse. The plasma lens was created by a nanosecond laser, which ablated a capillary entrance. The spatial configuration of the ablated plasma focused a high intensity femtosecond laser pulse. This configuration offers versatility in the plasma lens small f-number for extremely tight focusing of high power lasers with no damage threshold restrictions of regular optical components.
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52.75.-d Plasma devices
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.58.Lq Z-pinches, plasma focus, and other pinch devices

Coupled photonic crystal nanobeam cavities

Parag B. Deotare, Murray W. McCutcheon, Ian W. Frank, Mughees Khan, and Marko Lončar

Appl. Phys. Lett. 95, 031102 (2009); http://dx.doi.org/10.1063/1.3176442 (3 pages) | Cited 22 times

Online Publication Date: 20 July 2009

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We describe the design, fabrication, and spectroscopy of coupled, high quality (Q) factor silicon nanobeam photonic crystal cavities. We show that the single nanobeam cavity modes are coupled into even and odd superposition modes, and we simulate the frequency and Q factor as a function of nanobeam spacing, demonstrating that a differential wavelength shift of 70 nm between the two modes is possible while maintaining Q factors greater than 106. For both on substrate and freestanding nanobeams, we experimentally monitor the response of the even mode as the gap is varied, and measure Q factors as high as 2×105.
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42.70.Qs Photonic bandgap materials
42.82.Bq Design and performance testing of integrated-optical systems
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays

An optical beam frequency reference with 10−14 range frequency instability

J. J. McFerran, J. G. Hartnett, and A. N. Luiten

Appl. Phys. Lett. 95, 031103 (2009); http://dx.doi.org/10.1063/1.3184578 (3 pages) | Cited 2 times

Online Publication Date: 20 July 2009

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The authors report on a thermal beam optical frequency reference with a fractional frequency instability of 9.2×10−14 at 1 s reducing to 2.0×10−14 at 64 s before slowly rising. The 1S0↔3P1 intercombination line in neutral 40Ca is used as a frequency discriminator. A diode laser at 423 nm probes the ground state population after a Ramsey–Bordé sequence of 657 nm light-field interactions on the atoms. The measured fractional frequency instability is an order of magnitude improvement on previously reported thermal beam optical clocks. The photon shot-noise of the read-out produces a limiting square root Λ-variance of 7×10−14/math.
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06.30.Ft Time and frequency
06.20.fb Standards and calibration
37.20.+j Atomic and molecular beam sources and techniques
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
03.75.Be Atom and neutron optics

Characterization of terahertz field confinement at the end of a tapered metal wire waveguide

Victoria Astley, Rajind Mendis, and Daniel M. Mittleman

Appl. Phys. Lett. 95, 031104 (2009); http://dx.doi.org/10.1063/1.3186065 (3 pages) | Cited 14 times

Online Publication Date: 21 July 2009

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We present experimental verification of the possibility of strong subwavelength confinement of the terahertz electric field at the end of a tapered metal wire waveguide. The axial field component at the end of the tapered waveguide shows a lateral confinement that is an order of magnitude greater than an untapered waveguide, and over 100 times greater than the free-space wavelength. The axial component is also strongly confined in the propagation direction, in contrast to the radial field component. Comparison to numerical simulation yields excellent agreement when the effect of the detecting probe is included in the analysis.
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42.79.Gn Optical waveguides and couplers
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Photonic crystal distributed feedback quantum cascade lasers with 12 W output power

Y. Bai, B. Gokden, S. R. Darvish, S. Slivken, and M. Razeghi

Appl. Phys. Lett. 95, 031105 (2009); http://dx.doi.org/10.1063/1.3182567 (3 pages) | Cited 15 times

Online Publication Date: 21 July 2009

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We demonstrate room temperature, high power, and diffraction limited operation of photonic crystal distributed feedback (PCDFB) quantum cascade lasers emitting around 4.7 μm. PCDFB gratings with three distinctive periods are fabricated on the same wafer. Peak output power up to 12 W is demonstrated. Lasers with different periods show expected wavelength shifts according to the design. Dual mode spectra are attributed to a purer index coupling by putting the grating layer 100 nm away from the laser core. Single lobed diffraction limited far field profiles are observed.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.70.Qs Photonic bandgap materials

Highly reliable 500 mW laser diodes with epitaxially grown AlON coating for high-density optical storage

T. Kamikawa, Y. Kawaguchi, P. O. Vaccaro, S. Ito, and H. Kawanishi

Appl. Phys. Lett. 95, 031106 (2009); http://dx.doi.org/10.1063/1.3184595 (3 pages) | Cited 6 times

Online Publication Date: 21 July 2009

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Highly reliable operation of 405 nm laser diodes for high-density optical storage was demonstrated. Introduction of epitaxially grown AlON layer between the front facet and normal coating layer was shown to be effective to suppress catastrophic optical damage at the laser facet. Stable operation in excess of 1000 h was confirmed at an output power of 500 mW in a pulsed-mode at a case temperature of 80 °C.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Vb Optical storage systems, optical disks
42.79.Wc Optical coatings

Energy transfer and 1.54 μm emission in amorphous silicon nitride films

S. Yerci, R. Li, S. O. Kucheyev, T. van Buuren, S. N. Basu, and L. Dal Negro

Appl. Phys. Lett. 95, 031107 (2009); http://dx.doi.org/10.1063/1.3184790 (3 pages) | Cited 25 times

Online Publication Date: 22 July 2009

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Er-doped amorphous silicon nitride films with various Si concentrations (Er:SiNx) were fabricated by reactive magnetron cosputtering followed by thermal annealing. The effects of Si concentrations and annealing temperatures were investigated in relation to Er emission and excitation processes. Efficient excitation of Er ions was demonstrated within a broad energy spectrum and attributed to disorder-induced localized transitions in amorphous Er:SiNx. A systematic optimization of the 1.54 μm emission was performed and a fundamental trade-off was discovered between Er excitation and emission efficiency due to excess Si incorporation. These results provide an alternative approach for the engineering of sensitized Si-based light sources and lasers.
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78.66.Nk Insulators
78.55.Qr Amorphous materials; glasses and other disordered solids
64.70.K- Solid-solid transitions
81.40.Gh Other heat and thermomechanical treatments
81.15.Cd Deposition by sputtering
68.55.jd Thickness
61.72.up Other materials

Laser action from a sugar-threaded polyrotaxane

Marta M. Mróz, Stefano Perissinotto, Tersilla Virgili, Giuseppe Gigli, Marco Salerno, Michael J. Frampton, Giuseppe Sforazzini, Harry L. Anderson, and Guglielmo Lanzani

Appl. Phys. Lett. 95, 031108 (2009); http://dx.doi.org/10.1063/1.3179689 (3 pages) | Cited 10 times

Online Publication Date: 22 July 2009

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We present gain and lasing results from a polyrotaxane consisting of a conjugated polymer (polyfluorene-alt-biphenylene) threaded through sugar macrocycles (β-cyclodextrin). Encapsulation suppresses interchain charge separation, leading to lasing emission not observed in the unthreaded polymer, and enlargement of the stimulated emission in threaded polymer is observed. We demonstrate all-optical switching distributed feedback laser.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.70.Jk Polymers and organics

Optofluidic circular grating distributed feedback dye laser

Yan Chen, Zhenyu Li, M. David Henry, and Axel Scherer

Appl. Phys. Lett. 95, 031109 (2009); http://dx.doi.org/10.1063/1.3186786 (3 pages) | Cited 2 times

Online Publication Date: 22 July 2009

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We demonstrate an optically pumped surface emitting optofluidic dye laser using a second-order circular grating distributed feedback resonator. We present a composite bilayer soft lithography technique specifically developed for the fabrication of our dye laser and investigate a hybrid polymer material system [poly(dimethylsiloxane)/perfluoropolyether] to construct high-resolution Bragg gratings. Our lasers emit single frequency light at low lasing thresholds of 6 μJ/mm2. These optofluidic dye lasers can serve as low-cost and compact coherent light sources that are fully integrated within microfluidic analysis chips and provide an efficient approach to construct compact spectroscopy systems.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
42.70.Hj Laser materials
42.55.Px Semiconductor lasers; laser diodes
47.85.Np Fluidics
85.60.-q Optoelectronic devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Growth and characterization of InAsN/GaAs dilute nitride semiconductor alloys for the midinfrared spectral range

M. de la Mare, Q. Zhuang, A. Krier, A. Patanè, and S. Dhar

Appl. Phys. Lett. 95, 031110 (2009); http://dx.doi.org/10.1063/1.3187534 (3 pages) | Cited 10 times

Online Publication Date: 22 July 2009

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We report the growth of InAsN onto GaAs substrates using nitrogen plasma source molecular beam epitaxy. We describe the spectral properties of InAsN alloys with N-content in the range of 0%–1% and photoluminescence emission in the midinfrared spectral range. The photoluminescence emission of the sample containing 1% N reveals localized energy levels resonant with the conduction band states of InAsN.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.20.Nr Semiconductor compounds
68.55.ag Semiconductors
52.77.-j Plasma applications
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Damage of amorphous carbon induced by soft x-ray femtosecond pulses above and below the critical angle

J. Chalupský, V. Hájková, V. Altapova, T. Burian, A. J. Gleeson, L. Juha, M. Jurek, H. Sinn, M. Störmer, R. Sobierajski, K. Tiedtke, S. Toleikis, Th. Tschentscher, L. Vyšín, H. Wabnitz, et al.

Appl. Phys. Lett. 95, 031111 (2009); http://dx.doi.org/10.1063/1.3184785 (3 pages) | Cited 5 times

Online Publication Date: 23 July 2009

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We present results of damage studies conducted at the Free Electron LASer in Hamburg (FLASH) facility with 13.5 nm (91.8 eV) and 7 nm (177.1 eV) radiations. The laser beam was focused on a sample of 890-nm-thick amorphous carbon coated on a silicon wafer mimicking a x-ray mirror. The fluence threshold for graphitization was determined for different grazing angles above and below the critical angle. The observed angular dependence of Fth is explained by the variation in absorption depth and reflectivity. Moreover, the absorbed local dose needed for the phase transition leading to graphitization is shown to vary with the radiation wavelength.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.46.-w Structure of nanoscale materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
64.70.K- Solid-solid transitions

Mesa-isolated InGaAs photodetectors with low dark current

J. F. Klem, J. K. Kim, M. J. Cich, G. A. Keeler, S. D. Hawkins, and T. R. Fortune

Appl. Phys. Lett. 95, 031112 (2009); http://dx.doi.org/10.1063/1.3184807 (3 pages)

Online Publication Date: 23 July 2009

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We demonstrate InGaAs photodiodes with an epitaxial heterostructure that allows simple mesa isolation of individual devices with low dark current and high responsivity. An undoped InAlAs barrier and passivation layer enables isolation of detectors without exposing the InGaAs active region, while simultaneously reducing electron diffusion current. Photodetectors with mesa sizes as small as 25×25 μm2 exhibit dark current densities of 10 nA/cm2 at 295 K and responsivities of 0.62 A/W at 1550 nm.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
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Electron avalanches and diffused γ-mode in radio-frequency capacitively coupled atmospheric-pressure microplasmas

D. W. Liu, F. Iza, and M. G. Kong

Appl. Phys. Lett. 95, 031501 (2009); http://dx.doi.org/10.1063/1.3186073 (3 pages) | Cited 19 times

Online Publication Date: 20 July 2009

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Space-, time- and wavelength-resolved optical emission profiles suggest that the helium emission at 706 nm can be used to indicate the presence of high energy electrons and estimate the sheath in helium rf discharges containing small concentration of air impurities. Furthermore, the experimental data supports the theoretical predictions of energetic electron avalanches transiting across the discharge gap in rf microdischarges and the absence of an α-mode. Nonetheless, microdischarges sustained between bare metal electrodes and operating in the γ-mode can produce diffuse glowlike discharges rather than the typical radially constricted plasmas observed in millimeter-size rf atmospheric-pressure γ discharges.
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52.80.Pi High-frequency and RF discharges
52.80.Hc Glow; corona
52.25.Vy Impurities in plasmas
52.40.Kh Plasma sheaths
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
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Blueshift in optical band gap in nanocrystalline Zn1−xCaxO films deposited by sol-gel method

Kamakhya Prakash Misra, R. K. Shukla, Atul Srivastava, and Anchal Srivastava

Appl. Phys. Lett. 95, 031901 (2009); http://dx.doi.org/10.1063/1.3184789 (3 pages) | Cited 14 times

Online Publication Date: 20 July 2009

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A blueshift in the optical band gap of nanocrystalline Zn1−xCaxO thin films has been obtained. A 12.72% enhancement in the band gap of ZnO thin films has been obtained using Ca dopant for the first time. The band gap widens from 3.38 to 3.81 eV as the Ca concentration increases from x = 0 to x = 0.15. The films are deposited by sol-gel method and have a hexagonal wurtzite phase with no indication of calcium. Grain size lies in the range of 12–92 nm. Atomic force micrographs indicate much smaller rms surface roughness showing significantly smooth surfaces.
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78.66.Hf II-VI semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.35.bg Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds

Lattice polarity detection of InN by circular photogalvanic effect

Q. Zhang, X. Q. Wang, X. W. He, C. M. Yin, F. J. Xu, B. Shen, Y. H. Chen, Z. G. Wang, Y. Ishitani, and A. Yoshikawa

Appl. Phys. Lett. 95, 031902 (2009); http://dx.doi.org/10.1063/1.3186042 (3 pages) | Cited 3 times

Online Publication Date: 20 July 2009

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We report an effective and nondestructive method based on circular photogalvanic effect (CPGE) to detect the lattice polarity of InN. Because of the lattice inversion between In- and N-polar InN, the energy band spin splitting is opposite for InN films with different polarities. Consequently under light irradiation with the same helicity, CPGE photocurrents in In- and N-polar layers will have opposite directions, thus the polarity can be detected. This method is demonstrated by our CPGE measurements in both n- and p-type InN films.
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72.40.+w Photoconduction and photovoltaic effects
68.55.ag Semiconductors
61.80.-x Physical radiation effects, radiation damage
81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
81.05.Ea III-V semiconductors

Photoluminescence of highly excited AlN: Biexcitons and exciton-exciton scattering

R. A. R. Leute, M. Feneberg, R. Sauer, K. Thonke, S. B. Thapa, F. Scholz, Y. Taniyasu, and M. Kasu

Appl. Phys. Lett. 95, 031903 (2009); http://dx.doi.org/10.1063/1.3186044 (3 pages) | Cited 11 times

Online Publication Date: 20 July 2009

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Low-temperature photoluminescence spectra of nominally undoped high quality AlN layers on SiC and Al2O3 substrates are reported. Under high excitation conditions, we observe several bands that increase superlinearly with the excitation density. Based on temperature and excitation level dependences recorded on different samples, we identify a band 36 meV below the free A-exciton transition as due to exciton-exciton scattering (P2 band) and a second band down-shifted from the A-exciton transition by 27 meV as due to biexciton recombination. The combined data yield an exciton binding energy of 48 meV.
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71.35.Gg Exciton-mediated interactions
78.55.Cr III-V semiconductors

Electromechanical instability in semicrystalline polymers

Xuanhe Zhao and Zhigang Suo

Appl. Phys. Lett. 95, 031904 (2009); http://dx.doi.org/10.1063/1.3186078 (3 pages) | Cited 19 times

Online Publication Date: 20 July 2009

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When a layer of a semicrystalline polymer is subject to a tensile force in its plane and a voltage through its thickness, the deformation of the layer is initially homogeneous, but it then localizes. The electromechanical instability sets in when the force and the voltage reach critical conditions. The critical conditions are determined in this paper and are related to the following two special cases: the Considère condition for the necking instability and the Stark–Garton condition for the pull-in instability. The general critical conditions show that a tensile force can markedly reduce the critical voltage.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.41.+e Polymers, elastomers, and plastics
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Tuneable optical lenses from diamond thin films

A. Kriele, O. A. Williams, M. Wolfer, D. Brink, W. Müller-Sebert, and C. E. Nebel

Appl. Phys. Lett. 95, 031905 (2009); http://dx.doi.org/10.1063/1.3183534 (3 pages) | Cited 16 times

Online Publication Date: 20 July 2009

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Nanocrystalline diamond (NCD) membranes of 150 nm thickness and diameters in the millimeter range grown by microwave-assisted chemical-vapor deposition were bulged to investigate their mechanical properties and their use as tuneable optical lenses. The NCD films were grown at different CH4/H2 gas mixtures to vary the sp2/sp3 ratio and thereby to tune their mechanical, optical, and surface morphology properties. By applying gas over pressure the membrane forms a lens shaped geometry. From deflection data we calculated Young’s moduli which decrease with increasing CH4/H2 ratio from 1160 GPa at 0.5% to 900 GPa at 7%. Optical lens applications show a variation in the focal point from infinity to 3.5 mm. The data indicate that NCD is a promising material for tuneable optical lenses applications.
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42.79.-e Optical elements, devices, and systems

Photoluminescence and photoabsorption blueshift of nanostructured ZnO: Skin-depth quantum trapping and electron-phonon coupling

J. W. Li, X. J. Liu, L. W. Yang, Z. F. Zhou, G. F. Xie, Y. Pan, X. H. Wang, J. Zhou, L. T. Li, Likun Pan, Zhuo Sun, and Chang Q. Sun

Appl. Phys. Lett. 95, 031906 (2009); http://dx.doi.org/10.1063/1.3184566 (3 pages) | Cited 5 times

Online Publication Date: 20 July 2009

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Although the size- and shape-induced blueshift in the photoluminescence and photoabsorption of nanostructured ZnO has been extensively investigated, the underlying mechanism remains yet unclear. Here we show that theoretical reproduction of the observed trends clarifies that the blueshift originates from the Hamiltonian perturbation due to the broken-bond-induced local strain and quantum trapping and electron-phonon coupling in the surface skin up to two atomic layers in depth while bonds in the core interior retain their bulk nature. The extent of the blue shift depends on the tunable fraction of undercoordinated atoms in the surface skin. Therefore, the quantum confinement effect is indeed more “superficial” than first thought [ H. Winn, OE Mag. 8, 10 (2005) ].
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78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.38.-k Polarons and electron-phonon interactions
63.22.Kn Clusters and nanocrystals

Mechanism of strain relaxation by twisted nanocolumns revealed in AlGaN/GaN heterostructures

V. P. Kladko, A. V. Kuchuk, N. V. Safryuk, V. F. Machulin, A. E. Belyaev, H. Hardtdegen, and S. A. Vitusevich

Appl. Phys. Lett. 95, 031907 (2009); http://dx.doi.org/10.1063/1.3184569 (3 pages) | Cited 4 times

Online Publication Date: 20 July 2009

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The structural properties of AlGaN/GaN heterostructures grown by metal organic chemical vapor deposition on sapphire substrates with different thicknesses were studied by high-resolution x-ray diffraction. The relation between the deformations and dislocation densities in the layer and substrate was established. The dependence of the system’s curvature on the lattice mismatch, caused by different fractions of nanoblock twists with respect to the c-plane, was determined. A mechanism of elastic strain relaxation was proposed.
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62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Lk Linear defects: dislocations, disclinations
62.20.D- Elasticity
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Evidence of Germanium precipitation in phase-change Ge1−xTex thin films by Raman scattering

E. Gourvest, S. Lhostis, J. Kreisel, M. Armand, S. Maitrejean, A. Roule, and C. Vallée

Appl. Phys. Lett. 95, 031908 (2009); http://dx.doi.org/10.1063/1.3186077 (3 pages) | Cited 9 times

Online Publication Date: 21 July 2009

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In situ annealing Raman scattering is used to evidence germanium postcrystallization in the crystalline phase of Ge-rich phase-change GeTe thin films. Both reflectivity and Raman scattering show that the crystallization temperature of the as-deposited amorphous phase increases with increasing Ge content going from Tc = 180 °C (Ge0.5Te0.5) to 360 °C for Ge-rich Ge0.76Te0.24. The crystallized phase adopts the rhombohedral α-GeTe phase structure, and whatever the starting composition. For Ge-rich GeTe we observe a second characteristic temperature around 375 °C, which signs the crystallization of a precipitated cubic Ge phase and thus the presence of two distinct phases.
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81.30.Mh Solid-phase precipitation
64.70.kg Semiconductors
78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Twinning partial multiplication at grain boundary in nanocrystalline fcc metals

Y. T. Zhu, X. L. Wu, X. Z. Liao, J. Narayan, S. N. Mathaudhu, and L. J. Kecskés

Appl. Phys. Lett. 95, 031909 (2009); http://dx.doi.org/10.1063/1.3187539 (3 pages) | Cited 14 times

Online Publication Date: 22 July 2009

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Most deformation twins in nanocrystalline face-centered cubic (fcc) metals have been observed to form from grain boundaries. The growth of such twins requires the emission of Shockley partials from the grain boundary on successive slip planes. However, it is statistically improbable for a partial to exist on every slip plane. Here we propose a dislocation reaction and cross-slip mechanism on the grain boundary that would supply a partial on every successive slip plane for twin growth. This mechanism can also produce a twin with macrostrain smaller than that caused by a conventional twin.
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61.72.Mm Grain and twin boundaries
61.72.Lk Linear defects: dislocations, disclinations

The determination of the bulk residual doping in indium nitride films using photoluminescence

M. Moret, S. Ruffenach, O. Briot, and B. Gil

Appl. Phys. Lett. 95, 031910 (2009); http://dx.doi.org/10.1063/1.3187914 (3 pages) | Cited 9 times

Online Publication Date: 22 July 2009

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We extend to any temperature, the sophisticated calculation of the evolution of the 2 K photoluminescence energy of InN proposed by Arnaudov et al. [Phys. Rev. B 69, 115216 (2004) ], in view of determining the residual doping of thin films. From the detailed line shape modeling, we extract the full width at half maximum of the photoluminescence line which, in the first order, varies like n0.51 at low temperature. This allows us to propose a handy tool for rapid residual doping evaluation. Last, temperature and inhomogeneous broadening effects are analyzed. Ignoring the latter is shown to lead to an overestimation of the residual doping.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Enhanced absorption in one-dimensional phononic crystals with interfacial acoustic waves

B. J. Lee and A. C. To

Appl. Phys. Lett. 95, 031911 (2009); http://dx.doi.org/10.1063/1.3182819 (3 pages) | Cited 2 times

Online Publication Date: 22 July 2009

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The present study demonstrates that interfacial acoustic waves can be excited at the interface between two phononic crystals. The interfacial acoustic wave between two phononic crystals is analogous to the surface electromagnetic wave between two photonic crystals. While past works on phononic crystals exploit the unique bandgap phenomenon in periodic structures, the present work employs the Bloch wave in the stop band to excite interfacial acoustic waves that propagate along the interface and decay into both media. As a result, the interfacial wave can be employed in an effective wave filter in which the incident acoustic wave energy is guided by the interfacial wave to the lateral direction; thus, its propagation in the normal direction is inhibited. The advantage of using two phononic crystals is to excite the interfacial wave even at normal incidence.
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68.35.Iv Acoustical properties
71.20.-b Electron density of states and band structure of crystalline solids
63.20.-e Phonons in crystal lattices

Extension of the diffuse mismatch model for thermal boundary conductance between isotropic and anisotropic materials

John C. Duda, Justin L. Smoyer, Pamela M. Norris, and Patrick E. Hopkins

Appl. Phys. Lett. 95, 031912 (2009); http://dx.doi.org/10.1063/1.3189087 (3 pages) | Cited 21 times

Online Publication Date: 22 July 2009

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This model is an extension of the diffuse mismatch model (DMM), tailored to accurately predict thermal boundary conductance (hBD) at interfaces where one material comprising the interface is characterized by high elastic anisotropy. Temperature-dependent specific heat is calculated with this vibrational model and compared to published values. Modifications to the DMM that incorporate the vibrational model are presented with predictions of hBD at a metal-graphite interface. This model slightly underestimates experimental data, as expected, as the large acoustic mismatch between metals and graphite suggests inelastic scattering, something the DMM does not take into account.
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68.35.Ja Surface and interface dynamics and vibrations
73.40.Ns Metal-nonmetal contacts
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
68.35.Gy Mechanical properties; surface strains
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