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9 Feb 2004

Volume 84, Issue 6, pp. 837-1024

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 975 (2004); http://dx.doi.org/10.1063/1.1646453 (3 pages)

Xiang Yang Kong and Zhong Lin Wang
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Wavelength flipping in laser emission driven by a switchable holographic grating

D. E. Lucchetta, L. Criante, O. Francescangeli, and F. Simoni

Appl. Phys. Lett. 84, 837 (2004); http://dx.doi.org/10.1063/1.1645660 (3 pages) | Cited 23 times

Online Publication Date: 4 February 2004

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We report lasing from a simple wafer structure made of a thin layer of rhodamine 6G as active material and of a switchable holographic mirror, based on a reflection grating made of polymer dispersed liquid crystals. It is shown that switching-off the mirror reflectivity by application of a suitable voltage allows wavelength flipping of the laser emission by 10 nm. © 2004 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Df Liquid crystals
42.79.Bh Lenses, prisms and mirrors
42.55.Mv Dye lasers

Terahertz electro-optic wavelength conversion in GaAs quantum wells: Improved efficiency and room-temperature operation

S. G. Carter, V. Ciulin, M. S. Sherwin, M. Hanson, A. Huntington, L. A. Coldren, and A. C. Gossard

Appl. Phys. Lett. 84, 840 (2004); http://dx.doi.org/10.1063/1.1645662 (3 pages) | Cited 20 times

Online Publication Date: 4 February 2004

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A 4-μm-thick sample containing 50 GaAs/AlGaAs asymmetric coupled quantum wells was driven with a strong terahertz (THz) electric field of frequency ωTHz and probed with a near-infrared (NIR) laser of frequency ωNIR. The THz beam modulated the probe to generate sidebands at ωNIR+nωTHz, where n is an integer. Up to 0.2% of the NIR laser power was converted into the n = +1 sideband at 20 K, and sidebands were observed up to room temperature. The strong THz fields also induced changes in the NIR absorption of the sample. © 2004 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.67.De Quantum wells
78.20.Jq Electro-optical effects
42.55.Px Semiconductor lasers; laser diodes
78.30.Fs III-V and II-VI semiconductors

Adaptive geometric optics derived from nonlinear acoustic effects

Keith A. Higginson, Michael A. Costolo, and Edward A. Rietman

Appl. Phys. Lett. 84, 843 (2004); http://dx.doi.org/10.1063/1.1645663 (3 pages) | Cited 8 times

Online Publication Date: 4 February 2004

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Tunable gradient index (GRIN) lenses were formed in a liquid-filled cavity supporting an ultrasonic standing wave. The refractive index gradient is based on the steady-state pressure component of the finite-amplitude acoustic signal. An acoustic lens was constructed which (1) focused and modulated a collimated light source and (2) formed an image. The properties of the lens are a function of the amplitude and frequency of the applied ultrasound. At the center of symmetry, the device can be approximated as a diverging lens with a single focal point of about −10 cm. In general, however, a series of focal lines are formed, to create a device resembling an axicon or an abberrating lens. © 2004 American Institute of Physics.
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42.79.Ry Gradient-index (GRIN) devices
42.15.Fr Aberrations
43.25.Dc Nonlinear acoustics of solids
42.79.Bh Lenses, prisms and mirrors

Temperature tuning of the optical properties of planar photonic crystal microcavities

B. Wild, R. Ferrini, R. Houdré, M. Mulot, S. Anand, and C. J. M. Smith

Appl. Phys. Lett. 84, 846 (2004); http://dx.doi.org/10.1063/1.1645675 (3 pages) | Cited 38 times

Online Publication Date: 4 February 2004

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We report on the temperature tuning of the optical properties of photonic crystal (PhC) microcavities. Planar and one-dimensional cavities were made from two-dimensional PhCs etched in GaAs and InP based vertical waveguides. These systems were optically characterized by an internal light source technique. The samples were mounted on a Peltier stage in order to vary the temperature from 20 to 76 °C. Linear dependence of the resonance wavelengths with respect to the temperature is observed with gradients dλ/dT = 0.09 and 0.1 nm/°C for GaAs and InP based cavities, respectively. These results are in agreement with theoretical calculations based on the thermal dependence of the refractive index of the PhC semiconductor component. © 2004 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Broad-band polarization conversion from a finite periodic structure in the microwave regime

B. T. Hallam, C. R. Lawrence, I. R. Hooper, and J. R. Sambles

Appl. Phys. Lett. 84, 849 (2004); http://dx.doi.org/10.1063/1.1645661 (3 pages) | Cited 6 times

Online Publication Date: 4 February 2004

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A reflection grating demonstrating extraordinarily broad-band polarization conversion in a nondiffractive regime has been studied at microwave frequencies. This single-element structure has been fabricated by electrolessly plating a metallic layer onto a stereo-lithographically produced resin profile. Angle-dependent microwave reflectivity data collected from the grating indicates polarization conversion of greater than 80% over a spectral bandwidth equivalent to the entire visible regime (factor of 2 in frequency). This supports an earlier publication in which it was predicted that a broad-band polarization converter could be created from a suitably profiled diffraction grating. © 2004 American Institute of Physics.
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42.79.Dj Gratings
42.82.Cr Fabrication techniques; lithography, pattern transfer

Propagation loss measurement for surface plasmon-polariton modes at metal waveguides on semiconductor substrates

Touichiro Goto, Yoshitada Katagiri, Hiroshi Fukuda, Hiroyuki Shinojima, Yoshiaki Nakano, Ikutaro Kobayashi, and Yasuyuki Mitsuoka

Appl. Phys. Lett. 84, 852 (2004); http://dx.doi.org/10.1063/1.1645990 (3 pages) | Cited 23 times

Online Publication Date: 4 February 2004

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Propagation losses were measured for surface plasmon-polariton (SPP) modes at metal waveguides on semiconductor substrates. The waveguides are simple strips of Au or Al deposited on InP substrates or 300-nm-thick SiO2 film covering the InP substrates. We used a direct method that can clearly discriminate SPP modes in vidicon-camera images, thereby allowing quantitative measurements. The loss coefficients measured at a wavelength of 1.55 μm were, as predicted by theory, in the range of 8.5–17 dB/mm, which shows the waveguides are feasible for practical applications. © 2004 American Institute of Physics.
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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)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening

T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura

Appl. Phys. Lett. 84, 855 (2004); http://dx.doi.org/10.1063/1.1645992 (3 pages) | Cited 448 times

Online Publication Date: 4 February 2004

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Roughened surfaces of light-emitting diodes (LEDs) provide substantial improvement in light extraction efficiency. By using the laser-lift-off technique followed by an anisotropic etching process to roughen the surface, an n-side-up GaN-based LED with a hexagonal “conelike” surface has been fabricated. The enhancement of the LED output power depends on the surface conditions. The output power of an optimally roughened surface LED shows a twofold to threefold increase compared to that of an LED before surface roughening. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning

Phase conjugation by low-power continuous-wave degenerate four-wave mixing in nonlinear optical polymer fibers

Shaoping Bian and Mark G. Kuzyk

Appl. Phys. Lett. 84, 858 (2004); http://dx.doi.org/10.1063/1.1645995 (3 pages) | Cited 7 times

Online Publication Date: 4 February 2004

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We report on the observation of phase conjugation (PC) using low-power, continuous-wave degenerate four-wave mixing in nonlinear polymer multimode fibers. The fibers are made of poly(methyl methacrylate) doped with Disperse Red 1 as the photosensitive chromophore. With a power less than 2.5 mW at wavelength 633 nm for each beam inside the fiber, a maximum PC reflectivity of 1% is obtained. Phase conjugation is observed for both parallel and orthogonally polarized probe and pump beams. Experimental results show that polarization and intensity profile are preserved in the PC wave. The predominant phase conjugation wave is attributed to the formation of sub-refractive-index gratings inside the fibers. © 2004 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.81.Gs Birefringence, polarization
42.79.Dj Gratings

Highly directional emission from few-micron-size elliptical microdisks

Sun-Kyung Kim, Se-Heon Kim, Guk-Hyun Kim, Hong-Gyu Park, Dong-Jae Shin, and Yong-Hee Lee

Appl. Phys. Lett. 84, 861 (2004); http://dx.doi.org/10.1063/1.1646459 (3 pages) | Cited 24 times

Online Publication Date: 4 February 2004

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Few-micron-sized elliptically deformed InGaAsP–InP microdisk lasers are fabricated and highly directional emissions are observed along the direction perpendicular to the surface of highest curvature. As the size of the elliptical microdisk is reduced, both the azimuthal angular spreading and the number of lobes become smaller. The improved directionality of the smaller structure is attributed to the enhanced tunneling loss at the high curvature surfaces. The far-field radiation is linearly polarized. Charge-coupled-device images confirmed the existence of strong near-field emission in the vicinity of high curvature surfaces. © 2004 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.79.Pw Imaging detectors and sensors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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Discharge asymmetry induced by the pulsed radio-frequency current

H. C. Kim, J. K. Lee, and J. W. Shon

Appl. Phys. Lett. 84, 864 (2004); http://dx.doi.org/10.1063/1.1646458 (3 pages) | Cited 3 times

Online Publication Date: 4 February 2004

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Through particle-in-cell/Monte Carlo simulations, the discharge asymmetry induced by the pulsed radio-frequency (rf) form of the driving current is found in capacitively coupled plasmas. It is shown that this discharge asymmetry originates from the phase shift between the rf current and voltage during the current-on time. Consequently, the degree of the asymmetry can be controlled by varying the phase of the rf current. As the duty ratio decreases, the plasma density decreases but the dc bias increases. Hence, it is possible to control the ion flux and ion bombardment energy independently by varying both the amplitude of the rf current and the duty ratio. © 2004 American Institute of Physics.
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52.80.-s Electric discharges
52.25.-b Plasma properties
52.65.Pp Monte Carlo methods
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Scaling law for the compositional dependence of Raman frequencies in SnGe and GeSi alloys

S. F. Li, M. R. Bauer, J. Menéndez, and J. Kouvetakis

Appl. Phys. Lett. 84, 867 (2004); http://dx.doi.org/10.1063/1.1645667 (3 pages) | Cited 10 times

Online Publication Date: 4 February 2004

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The compositional dependence of the Ge–Ge Raman mode in SnGe alloys has been measured in samples grown on Si substrates using a chemical vapor deposition technique. The experimental result, Δω(s) = (−68±5)s (where s is the Sn concentration), is in very good agreement with a theoretical prediction from a simple model with parameters adjusted to the compositional dependence of Raman frequencies in GeSi alloys. © 2004 American Institute of Physics.
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78.30.Am Elemental semiconductors and insulators
78.66.Li Other semiconductors

Transmission electron microscopy and Raman measurements of the misfit stress in a Si tensile strained layer

M. Cabié, A. Ponchet, A. Rocher, V. Paillard, and L. Vincent

Appl. Phys. Lett. 84, 870 (2004); http://dx.doi.org/10.1063/1.1644639 (3 pages) | Cited 4 times

Online Publication Date: 4 February 2004

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A tensile-strained Si layer grown on a Si0.8Ge0.2 pseudo substrate with a nominal lattice mismatch of −0.76% has been studied by transmission electron microscopy using a curvature method and Raman scattering in order to determine experimentally the in-plane component of the epitaxial stress. The stress is obtained by measuring the curvature and the thickness on different areas of a thinned sample. Experimental values of the stress given by the two methods are in good agreement and are close to the nominal one. © 2004 American Institute of Physics.
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78.30.Am Elemental semiconductors and insulators
68.60.Bs Mechanical and acoustical properties

Parametric study on optical properties of digital-alloy In(Ga1−zAlz)As/InP grown by molecular-beam epitaxy

J. D. Song, D. C. Heo, I. K. Han, J. M. Kim, Y. T. Lee, and S.-H. Park

Appl. Phys. Lett. 84, 873 (2004); http://dx.doi.org/10.1063/1.1645666 (3 pages) | Cited 1 time

Online Publication Date: 4 February 2004

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Optical properties of digital-alloy InGaAlAs grown by molecular-beam epitaxy were parametrically investigated by 10-K-photoluminescence (PL) study on (In0.53Ga0.47As)n/(In0.52Al0.48As)n short-period superlattices (SPSs) in the range of n = 1–5 monolayers. Two different peaks are resolved in PL spectra, and the higher energy peak (H) results from an excitonic transition while the lower energy peak (L) is related to a phonon-assisted transition. The H peak energies decrease monotonously as n increases, and it is in good agreement with the band-gap calculation with transfer matrix methods. It is found that two monolayer-period length (n = 2) is the optimum one, where the PL intensity is largest and the ratio of L peak to H peak intensity is lowest. The various compositions (z) of digital-alloy In(Ga1−zAlz)As are prepared and their optical properties are investigated for z = 0.2, 0.4, 0.6, and 0.8. The linewidths of 9-K-PL spectra for various z values are within the range of 10–15 meV, which are comparable to the best analog-alloy InGaAlAs. © 2004 American Institute of Physics.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
73.21.Cd Superlattices
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
78.66.Fd III-V semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Modeling of Si self-diffusion in SiO2: Effect of the Si/SiO2 interface including time-dependent diffusivity

Masashi Uematsu, Hiroyuki Kageshima, Yasuo Takahashi, Shigeto Fukatsu, Kohei M. Itoh, Kenji Shiraishi, and Ulrich Gösele

Appl. Phys. Lett. 84, 876 (2004); http://dx.doi.org/10.1063/1.1644623 (3 pages) | Cited 22 times

Online Publication Date: 4 February 2004

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Self-diffusion of Si in thermally grown SiO2 is modeled taking into account the effect of SiO molecules generated at the Si/SiO2 interface and diffusing into SiO2 to enhance the self-diffusion. Based on the model, a recent self-diffusion experiment of ion-implanted 30Si in SiO2, which showed increasing self-diffusivity with decreasing distance between the 30Si diffusers and Si/SiO2 interface [Fukatsu et al., Appl. Phys. Lett. 83, 3897 (2003)], was simulated, and the simulated results fit the experimental profiles. Furthermore, the simulation predicts that the self-diffusivity would increase for a longer annealing time because more SiO molecules should be arriving from the interface. Such time-dependent diffusivity was indeed found in our follow-up experiments, and the profiles were also fitted by the simulation using a single set of parameters. © 2004 American Institute of Physics.
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66.30.Dn Theory of diffusion and ionic conduction in solids
66.30.H- Self-diffusion and ionic conduction in nonmetals
68.35.Ct Interface structure and roughness
61.72.Cc Kinetics of defect formation and annealing
61.72.up Other materials

Third-order optical nonlinearity originating from room-temperature exciton in layered compounds LaCuOS and LaCuOSe

Hayato Kamioka, Hidenori Hiramatsu, Hiromichi Ohta, Masahiro Hirano, Kazushige Ueda, Toshio Kamiya, and Hideo Hosono

Appl. Phys. Lett. 84, 879 (2004); http://dx.doi.org/10.1063/1.1646221 (3 pages) | Cited 24 times

Online Publication Date: 4 February 2004

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We have studied the third-order optical nonlinearity (χ(3)) of epitaxial thin films of layered compounds LaCuOS and LaCuOSe at room temperature by a spectrally resolved degenerative four-wave mixing technique with femtosecond time resolution. The χ(3) values in both films are sharply resonant to optical absorption bands in the ultraviolet (UV) light region due to room-temperature exciton. The peak values are evaluated to be as large as 2–4×10−9 esu with a fast time response of 250–300 fs. These findings indicate that LaCuOS and LaCuOSe are promising materials for emerging optical nonlinear devices that operate in the UV light region compatible for GaN-based lasers. © 2004 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
68.55.-a Thin film structure and morphology
42.70.Mp Nonlinear optical crystals
78.40.Ha Other nonmetallic inorganics

Very fast YbxY1−xAlO3 single-crystal scintillators

M. Nikl, N. Solovieva, J. Pejchal, J. B. Shim, A. Yoshikawa, T. Fukuda, A. Vedda, M. Martini, and D. H. Yoon

Appl. Phys. Lett. 84, 882 (2004); http://dx.doi.org/10.1063/1.1645987 (3 pages) | Cited 13 times

Online Publication Date: 4 February 2004

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Scintillation, radioluminescence, photoluminescence, and thermoluminescence characteristics of Czochralski-grown YbxY1−xAlO3 single crystals for x = 0.02–0.45 are described. Under x-ray excitation, the intensity of Yb3+ charge-transfer luminescence is increasing with x and reaches at room temperature more than 11% of Bi4Ge3O12 (BGO) for x = 0.45, while at 80 K it is over 170% of BGO for x ≥ 0.3. At room temperature, scintillation decay shows a dominant decay time of 0.8–0.9 ns for x ≥ 0.3 and no significant slow components were detected. The photoluminescence decay time is tuned by temperature and Yb concentration from tens of nanoseconds at 80 K down to about 0.8 ns at 295 K. Thermoluminescence glow curve below room temperature evidences very low concentration of shallow traps compared to the Ce-doped YAlO3 scintillator. © 2004 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.60.Kn Thermoluminescence
78.47.-p Spectroscopy of solid state dynamics
71.70.Gm Exchange interactions

Ordering parameters of self-organized three-dimensional quantum-dot lattices determined from anomalous x-ray diffraction

R. T. Lechner, T. U. Schülli, V. Holý, G. Springholz, J. Stangl, A. Raab, G. Bauer, and T. H. Metzger

Appl. Phys. Lett. 84, 885 (2004); http://dx.doi.org/10.1063/1.1644627 (3 pages) | Cited 7 times

Online Publication Date: 4 February 2004

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Anomalous x-ray diffraction is used to investigate self-organized ordering of PbSe/PbEuTe quantum dot superlattices in which different ordered structures form for different PbSe dot layer spacings. Using a theoretical dot ordering model, the different ordering parameters are determined from the x-ray spectra. © 2004 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
68.65.Cd Superlattices
61.72.Nn Stacking faults and other planar or extended defects

Optical and structural properties of SixSnyGe1−x−y alloys

P. Aella, C. Cook, J. Tolle, S. Zollner, A. V. G. Chizmeshya, and J. Kouvetakis

Appl. Phys. Lett. 84, 888 (2004); http://dx.doi.org/10.1063/1.1645324 (3 pages) | Cited 18 times

Online Publication Date: 4 February 2004

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Single-phase SixSnyGe1−x−y alloys (x ⩽ 0.25,y ⩽ 0.11) were grown on Si using chemical vapor deposition. First principles simulations predict that these materials are thermodynamically accessible and yield lattice constants as a function of Si/Sn concentrations in good agreement with experiment. An empirical model derived from experimental SixGe1−x and SnyGe1−y binary data also provides a quantitative description of the composition dependence of the lattice parameters. Spectroscopic ellipsometry of selected samples yields dielectric functions indicating a band structure consistent with highly crystalline semiconductor materials of diamond symmetry. Incorporation of Si into SnyGe1−y leads to an additional reduction of the E2 critical point, as expected based on the E2 values of Si and Ge. © 2004 American Institute of Physics.
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78.66.Li Other semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
77.22.Ch Permittivity (dielectric function)
73.20.At Surface states, band structure, electron density of states
81.05.Hd Other semiconductors
68.55.-a Thin film structure and morphology

Ultrafast conductivity dynamics in pentacene probed using terahertz spectroscopy

V. K. Thorsmølle, R. D. Averitt, X. Chi, D. J. Hilton, D. L. Smith, A. P. Ramirez, and A. J. Taylor

Appl. Phys. Lett. 84, 891 (2004); http://dx.doi.org/10.1063/1.1644046 (3 pages) | Cited 22 times

Online Publication Date: 4 February 2004

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We present measurements of the transient photoconductivity in pentacene single crystals using optical-pump terahertz-probe spectroscopy. We have measured the temperature and fluence dependence of the mobility of the photoexcited charge carriers with picosecond resolution. The pentacene crystals were excited at 3.0 eV, which is above the bandgap of ∼ 2.2 eV, and the induced change in the far-infrared transmission was measured. At 30 K, the carrier mobility is μ ≈ 0.4 cm2/V s and decreases to μ ≈ 0.2 cm2/V s at room temperature. The transient terahertz signal reveals the presence of free carriers that are trapped on the time scale of a few picoseconds or less, possibly through the formation of excitons, small polarons, or trapping by impurities. © 2004 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
72.40.+w Photoconduction and photovoltaic effects
71.20.Rv Polymers and organic compounds
71.35.-y Excitons and related phenomena
61.72.S- Impurities in crystals

Ion irradiation effects on the mechanical stability of compressed metallic thin films

P. Goudeau, M. George, and C. Coupeau

Appl. Phys. Lett. 84, 894 (2004); http://dx.doi.org/10.1063/1.1645981 (3 pages) | Cited 1 time

Online Publication Date: 4 February 2004

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Residual stresses in materials and components such as thin films in microelectromechanical systems are developed during the production process and may drastically limit their functionality and lifetime; their minimization is thus of utmost technical importance. Ion beam irradiation in polycrystalline Mo thin films sputter-deposited on (100) silicon wafer at room temperature has been used to reduce the residual stresses present in the layer and thus to improve the mechanical stability of the film/substrate set. Although a strong reduction of residual stresses in the whole film is evidenced, irradiation affects the film-substrate bond strength; defect creation at the film-substrate interface due to ion implantation induces thin-film delamination. © 2004 American Institute of Physics.
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61.80.Jh Ion radiation effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.82.Bg Metals and alloys
68.60.Bs Mechanical and acoustical properties
61.72.J- Point defects and defect clusters
68.35.Ct Interface structure and roughness

Local vibrational modes of H complexes in Mg-doped GaN grown by molecular beam epitaxy

R. Cuscó, L. Artús, D. Pastor, F. B. Naranjo, and E. Calleja

Appl. Phys. Lett. 84, 897 (2004); http://dx.doi.org/10.1063/1.1645668 (3 pages) | Cited 5 times

Online Publication Date: 4 February 2004

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Local vibrational modes (LVM’s) in Mg-doped GaN grown by molecular beam epitaxy have been studied by Raman scattering. Besides Mg local vibrational modes, several local mode peaks associated with hydrogen complexes are observed in the region around 2200 cm−1 and peaks assigned to carbon-hydrogen complexes are also detected in the region around 2900 cm−1. These modes arise from the presence of unintentional carbon and hydrogen impurities in the sample, which was corroborated by secondary ion mass spectroscopy measurements. Raman scattering evidence of local vibrational modes of the C-H complex in GaN is reported. The behavior of the LVM’s associated with the hydrogen and carbon impurity complexes with annealing temperature is also reported. © 2004 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.55.Eq III-V semiconductors

Nonlinear propagation of ultrafast 1.5 μm pulses in high-index-contrast silicon-on-insulator waveguides

Georg W. Rieger, Kuljit S. Virk, and Jeff F. Young

Appl. Phys. Lett. 84, 900 (2004); http://dx.doi.org/10.1063/1.1645991 (3 pages) | Cited 54 times

Online Publication Date: 4 February 2004

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Propagation through silicon-on-insulator (SOI) waveguide structures of 1.53 μm, 100 fs laser pulses with peak powers up to 400 W is studied experimentally and theoretically. The dominant nonlinear effects are two-photon absorption and self-phase modulation. The two-photon absorption coefficient and the nonlinear refractive index of Si obtained in this work are β2 = 0.9 cm/GW and n2 = 0.7×10−13 cm2/W, respectively. At high intensities, free carriers generated by two-photon absorption are demonstrated to have a significant influence on pulse spectra and transmitted power. The figure of merit for all-optical switching obtained in this work (T = 1.8) indicates that a switch based on a SOI waveguide structure might be possible at 1.55 μm. © 2004 American Institute of Physics.
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42.25.Bs Wave propagation, transmission and absorption
42.79.Gn Optical waveguides and couplers
42.65.Wi Nonlinear waveguides
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Enhancement of 1.54 μm photoluminescence observed in Al-doped β-FeSi2

Yoshikazu Terai and Yoshihito Maeda

Appl. Phys. Lett. 84, 903 (2004); http://dx.doi.org/10.1063/1.1646215 (3 pages) | Cited 13 times

Online Publication Date: 4 February 2004

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We present photoluminescence (PL) properties of impurity (Al, Mn, Co)-doped β-FeSi2 produced by ion-beam synthesis. The β-Fe(Si1−xAlx)2 sample showed an increase of both the PL intensity and activation energy (Ea) for a nonradiative recombination path. On the contrary, the β-(Fe1−xMnx)Si2 and the β-(Fe1−xCox)Si2 samples reduced the PL intensity and Ea. We found that the doping of Al atoms occupying the Si sites in β-FeSi2 is effective to enhance the 1.54 μm photoluminescence. © 2004 American Institute of Physics.
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61.72.S- Impurities in crystals
78.55.Hx Other solid inorganic materials
61.80.Jh Ion radiation effects

Tensile strained epitaxial Ge films on Si(100) substrates with potential application in L-band telecommunications

Douglas D. Cannon, Jifeng Liu, Yasuhiko Ishikawa, Kazumi Wada, David T. Danielson, Samerkhae Jongthammanurak, Jurgen Michel, and Lionel C. Kimerling

Appl. Phys. Lett. 84, 906 (2004); http://dx.doi.org/10.1063/1.1645677 (3 pages) | Cited 34 times

Online Publication Date: 4 February 2004

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Tensile strained epitaxial Ge films were grown on Si(100) substrates by ultra-high vacuum chemical vapor deposition. The tensile strain was induced by the thermal expansion coefficient mismatch between Si and Ge during the cooling process from elevated growth temperatures, which induces narrowing of the Ge direct band gap, EgΓ, and pushes the absorption spectrum of Ge toward longer wavelengths. The EgΓ versus strain relation was measured experimentally by photoreflectance and x-ray diffraction, and the result agrees well with calculations by deformation potential theory. With an in-plane tensile strain of 0.21%, the EgΓ of the Ge film grown at 800 °C decreased from 32 meV to 0.768 eV compared with 0.80 for bulk Ge, and corresponded to an absorption edge at 1610 nm. The broadened absorption spectrum of tensile strained Ge makes it promising as a Si-compatible photodector material for L-band (1560–1620 nm) optical communications. © 2004 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
65.40.De Thermal expansion; thermomechanical effects
78.40.Fy Semiconductors
68.60.Bs Mechanical and acoustical properties
71.20.Mq Elemental semiconductors
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Cy Elemental semiconductors

Reduced SnO2 surfaces by first-principles calculations

Wolfgang Bergermayer and Isao Tanaka

Appl. Phys. Lett. 84, 909 (2004); http://dx.doi.org/10.1063/1.1646460 (3 pages) | Cited 28 times

Online Publication Date: 4 February 2004

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SnO2(110) and (101) surfaces with eleven different kinds of terminations for each are systematically investigated by a first-principles projector augmented wave method. Surface energies are discussed as a function of temperature and oxygen partial pressure. Atomic relaxations of the surfaces are then compared. In agreement with previous calculations, the stoichiometric (110) surface is the most stable surface at high oxygen chemical potentials (i.e., low temperature or high pressure). At lower oxygen chemical potentials, however, one of the reduced (101) surface terminations becomes energetically preferred. The other surface terminations are found to be less stable. This is consistent with recent thin-film experimental results. © 2004 American Institute of Physics.
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61.66.Bi Elemental solids
61.66.Dk Alloys
68.35.Md Surface thermodynamics, surface energies
65.40.G- Other thermodynamical quantities
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