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15 Mar 2004

Volume 84, Issue 11, pp. 1817-2002

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 1952 (2004); http://dx.doi.org/10.1063/1.1669071 (3 pages)

M. Feng, N. Holonyak, and R. Chan
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Rapid photon flux switching in two-dimensional photonic crystals

X. Wang, K. Kempa, Z. F. Ren, and B. Kimball

Appl. Phys. Lett. 84, 1817 (2004); http://dx.doi.org/10.1063/1.1667593 (3 pages) | Cited 10 times

Online Publication Date: 10 March 2004

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We have investigated the out-of-plane propagation of light in two-dimensional photonic band-gap crystals consisting of long dielectric nanorods. Defects, which sufficiently break the crystal symmetry, can produce photonic states localized at the defect sites. We show that this localization can result in a sharp transition between the state of the out-of-plane light propagation through the entire photonic crystal, and the state in which light propagates only along the defect channels. This switching can be induced by slight changes of the dielectric constant at the defect sites. We propose a practical way of achieving this, and suggest applications. © 2004 American Institute of Physics.
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42.70.Qs Photonic bandgap materials

Control of optical polarization anisotropy in edge emitting luminescence of InAs/GaAs self-assembled quantum dots

P. Jayavel, H. Tanaka, T. Kita, O. Wada, H. Ebe, M. Sugawara, J. Tatebayashi, Y. Arakawa, Y. Nakata, and T. Akiyama

Appl. Phys. Lett. 84, 1820 (2004); http://dx.doi.org/10.1063/1.1675923 (3 pages) | Cited 29 times

Online Publication Date: 10 March 2004

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We have studied the polarization properties of cleaved-edge photoluminescence (PL) from InAs/GaAs self-assembled quantum dots. Transverse-electric (TE) and transverse-magnetic (TM) mode PL intensities have been analyzed for the dots having 8 nm InxGa1−xAs capping layer with indium (In) composition of x = 0 and 0.13. Polarization results show a dramatic change with the capping layer In compositions; TE-mode dominant PL is observed for dots with x = 0, on the other hand, TM-mode dominant PL for dots with x = 0.13. This polarization change has been attributed to the dot shape change using transmission electron microscopy images. These results suggest that the optical polarization anisotropy of the quantum dots can be controlled by manipulating the capping layer In composition. © 2004 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Enhanced electro-optic effect in GaInAsP–InP three-step quantum wells

H. Mohseni, H. An, Z. A. Shellenbarger, M. H. Kwakernaak, and J. H. Abeles

Appl. Phys. Lett. 84, 1823 (2004); http://dx.doi.org/10.1063/1.1682699 (3 pages) | Cited 10 times

Online Publication Date: 10 March 2004

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We report on the enhanced electro-optic coefficient of GaInAsP three-step quantum wells (3SQW) for high power electrorefraction modulator applications. Measured electro-optic coefficient of the 3SQW is nearly three times higher than the conventional rectangular quantum well (RQW) at λ = 1.55 μm. The enhanced electro-optic effect, combined with a low optical absorption coefficient α<1 cm−1 in the 3SQW increases a modulator figure of merit by nearly 36 times, and decreases the power consumption by nearly one order of magnitude compared with a conventional RQW design. © 2004 American Institute of Physics.
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78.20.Jq Electro-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Hp Optical processors, correlators, and modulators

Theoretical study of Auger recombination in a GaInNAs 1.3 μm quantum well laser structure

A. D. Andreev and E. P. O’Reilly

Appl. Phys. Lett. 84, 1826 (2004); http://dx.doi.org/10.1063/1.1664033 (3 pages) | Cited 10 times

Online Publication Date: 10 March 2004

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We present a theoretical study of Auger recombination processes in a GaInNAs/GaAs quantum well structure designed for 1.3 μm laser emission. The calculations are based on a 10×10 k⋅p model, incorporating valence, conduction, and nitrogen-induced bands. The Auger transition matrix elements are calculated explicitly, without introducing any further approximations into the Hamiltonian used. We consider two main Auger recombination channels: the process when the energy released from the electron-hole recombination causes electron excitation (CHCC process) and the process with hole excitation to the split-off valence band (CHHS process). The CHHS process is shown to be dominant. Good agreement is found when comparing the calculated Auger rates with experimental values of the Auger contribution to the threshold current of GaInNAs quantum well lasers. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.21.Fg Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
79.20.Fv Electron impact: Auger emission

Measurement of orientation dependent stress-optic coefficient of GaAs single crystals

H. J. Peng, S. P. Wong, H. P. Ho, and Shounan Zhao

Appl. Phys. Lett. 84, 1829 (2004); http://dx.doi.org/10.1063/1.1675938 (3 pages) | Cited 2 times

Online Publication Date: 10 March 2004

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The stress-optic coefficient C for (001) and (111) GaAs single crystal wafers at various observation directions was measured precisely using a simple four-point bending technique. Our experimental values of C for (001) GaAs wafers vary from 0.65×10−12 cm2/dyn (at 〈100〉 directions) to 1.43×10−12 cm2/dyn (at 〈110〉 directions). For (111) GaAs wafers, the experimental values of C show much smaller dependence on the observation direction and vary from 1.97×10−12 cm2/dyn (at 〈112〉 directions) to 2.11×10−12 cm2/dyn (at 〈110〉 directions). The combinations of piezo-optic coefficients π11–π12 and π44 were also derived from C for GaAs. © 2004 American Institute of Physics.
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78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Near-field optical study of AlGaN/GaN quantum-well waveguide

J. Shakya, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 84, 1832 (2004); http://dx.doi.org/10.1063/1.1675936 (3 pages) | Cited 2 times

Online Publication Date: 10 March 2004

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Ultraviolet near-field scanning microscopy and near-field spectroscopy have been employed to study the optical properties of AlGaN/GaN quantum-well waveguides. The divergence of the spontaneous emission emerging from the waveguide exit port was measured. The near-field optical image revealed a half-angle in-plane divergence of 6° and vertical divergence of 40°. Optical loss of the spontaneous emission inside the waveguide at λ = 350 nm was found to be 106 cm−1. These parameters are important for the achievement of future III-nitride photonic integrated circuits for various applications. © 2004 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Gn Optical waveguides and couplers
68.37.Uv Near-field scanning microscopy and spectroscopy

Surface plasmon polariton propagation around bends at a metal–dielectric interface

K. Hasegawa, J. U. Nöckel, and M. Deutsch

Appl. Phys. Lett. 84, 1835 (2004); http://dx.doi.org/10.1063/1.1675940 (3 pages) | Cited 13 times

Online Publication Date: 10 March 2004

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We analyze theoretically the propagation of surface plasmon polaritons about a metallic corner with a finite bend radius, using a one-dimensional model analogous to the scattering from a finite-depth potential well. We obtain expressions for the energy reflection and transmission coefficients in the short wavelength limit, as well as an upper bound for the transmittance. In certain cases we find that propagation on nonplanar interfaces may result in lower losses than on flat surfaces, contrary to expectation. In addition, we also find that the maximum transmittance depends nonmonotonously on the bend radius, allowing increased transmission with decreasing radius. © 2004 American Institute of Physics.
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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)

Microfluidic tunable photonic band-gap device

P. Domachuk, H. C. Nguyen, B. J. Eggleton, M. Straub, and M. Gu

Appl. Phys. Lett. 84, 1838 (2004); http://dx.doi.org/10.1063/1.1667592 (3 pages) | Cited 37 times

Online Publication Date: 10 March 2004

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We introduce a method for tuning a photonic band-gap material by means of displacing microfluidic plugs. The fluid is introduced into air voids that constitute the structure of the photonic crystal and is displaced using a capillary heater. The photonic crystal geometry is obtained using a microstructured optical fiber, comprising a periodically spaced array of air holes that is interrogated in the transverse direction, creating a “tall microchip.” Optical spectra are compared to band structure calculations of an idealized band-gap material. © 2004 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

High-power AlGaInP light-emitting diodes with metal substrates fabricated by wafer bonding

Wei Chih Peng and YewChung Sermon Wu

Appl. Phys. Lett. 84, 1841 (2004); http://dx.doi.org/10.1063/1.1682696 (3 pages) | Cited 9 times

Online Publication Date: 10 March 2004

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High-power light-emitting diodes (LEDs) fabricated on Cu substrates were investigated in this study. The AlGaInP LED structure was bonded to a Cu substrate by using indium-tin-oxide as the diffusion barrier layer. It was found that Cu-substrate-bonded LED devices could be operated in a much higher injection forward current, 800 mA, which was eight times higher than that used in traditional GaAs-substrate LEDs. The luminous intensity of the Cu-substrate LEDs could reach as high as 1230 mcd, which was three times higher than that of the GaAs-substrate LEDs. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.30.-z Semiconductor devices

Electrically tunable lasing based on defect mode in one-dimensional photonic crystal with conducting polymer and liquid crystal defect layer

Ryotaro Ozaki, Yuko Matsuhisa, Masanori Ozaki, and Katsumi Yoshino

Appl. Phys. Lett. 84, 1844 (2004); http://dx.doi.org/10.1063/1.1686891 (3 pages) | Cited 24 times

Online Publication Date: 10 March 2004

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Electrical tuning of the wavelength of the defect mode lasing in a one-dimensional photonic crystal has been demonstrated using a conducting polymer as an active emission layer and a nematic liquid crystal as an electrically tunable defect layer in the periodic structure. Lasing wavelength is widely tuned upon applying the electric field, which follows a defect mode shift due to the refractive index change in the nematic liquid crystal defect layer caused by field-induced realignment of the liquid crystal molecules. © 2004 American Institute of Physics.
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42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
42.70.Df Liquid crystals
42.25.Gy Edge and boundary effects; reflection and refraction
42.60.Fc Modulation, tuning, and mode locking
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Coherent grazing exit x-ray scattering geometry for probing the structure of thin films

Franz Pfeiffer, Wei Zhang, and Ian K. Robinson

Appl. Phys. Lett. 84, 1847 (2004); http://dx.doi.org/10.1063/1.1669061 (3 pages) | Cited 5 times

Online Publication Date: 10 March 2004

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We demonstrate a diffraction geometry which provides strong sensitivity to the microstructure of thin films. While a coherent beam of x rays is being reflected from the surface of the sample, measurements were made of the scattering of the exit beam below the critical angle for total external reflection. This results in a strong signal with speckle modulations that are characteristic of the internal arrangement of grains at different depths within the film. © 2004 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.70.Ck X-ray scattering

Comparison of structure and properties of femtosecond and nanosecond laser-structured silicon

C. H. Crouch, J. E. Carey, J. M. Warrender, M. J. Aziz, E. Mazur, and F. Y. Génin

Appl. Phys. Lett. 84, 1850 (2004); http://dx.doi.org/10.1063/1.1667004 (3 pages) | Cited 71 times

Online Publication Date: 10 March 2004

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We compare the optical properties, chemical composition, and crystallinity of silicon microstructures formed in the presence of SF6 by femtosecond laser irradiation and by nanosecond laser irradiation. In spite of very different morphology and crystallinity, the optical properties and chemical composition of the two types of microstructures are very similar. The structures formed with femtosecond (fs) pulses are covered with a disordered nanocrystalline surface layer less than 1 μm thick, while those formed with nanosecond (ns) pulses have very little disorder. Both ns-laser-formed and fs-laser-formed structures absorb near-infrared (1.1–2.5 μm) radiation strongly and have roughly 0.5% sulfur impurities. © 2004 American Institute of Physics.
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68.47.Fg Semiconductor surfaces
61.72.uf Ge and Si
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
78.30.Am Elemental semiconductors and insulators

Local self-organization of islands in embedded nanodot systems

Jianjun Zhang, Kaiwang Zhang, and Jianxin Zhong

Appl. Phys. Lett. 84, 1853 (2004); http://dx.doi.org/10.1063/1.1669079 (3 pages) | Cited 10 times

Online Publication Date: 10 March 2004

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We show that strain distribution on the surface of an isotropic spacer layer induced by an embedded island of large base-to-height aspect ratio deviates significantly from the description of the point force dipole model in the regime of small spacer layer thickness. In this regime, the strain profile displays several local maxima above the embedded island. The regions with local strain maxima serve as nucleation centers for growth of surface islands under appropriate growth conditions, resulting in locally well-organized surface islands above the embedded island. Our theoretical results are in excellent agreement with recent experiments for Ge islands embedded in Si. © 2004 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.43.Fg Adsorbate structure (binding sites, geometry)
64.60.Q- Nucleation
61.46.-w Structure of nanoscale materials

Formation of spinel from olivine

Zongwen Liu, Patrick M. Kelly, John Drennan, Peter Mora, and Hisao Kanda

Appl. Phys. Lett. 84, 1856 (2004); http://dx.doi.org/10.1063/1.1675939 (3 pages)

Online Publication Date: 10 March 2004

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High-resolution transmission electron microscopy (HRTEM) was used to study the olivine to spinel transformation. HRTEM structure images of Mg2GeO4 olivine deformed under a pressure of 6 GPa at 600 °C clearly show that a shear mechanism dominates the transformation. The transformation is not a nucleation and growth mechanism. It also differs in certain crucial aspects from the type of martensitic transformation proposed before. During the transformation, it is a shear movement that brings the oxygen anions to their positions in the spinel structure. An edge dislocation following each shear then puts the cations in their spinel sites. The Burgers’ vector of each dislocation is perpendicular to the anion shear direction. © 2004 American Institute of Physics.
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81.30.Kf Martensitic transformations
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Nonradiative recombination centers in Ga(As,N) and their annealing behavior studied by Raman spectroscopy

M. Ramsteiner, D. S. Jiang, J. S. Harris, and K. H. Ploog

Appl. Phys. Lett. 84, 1859 (2004); http://dx.doi.org/10.1063/1.1669070 (3 pages) | Cited 18 times

Online Publication Date: 10 March 2004

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Nitrogen-related defects in diluted Ga(As,N) have been detected by Raman scattering in resonance with the localized E+ transition. These defects are attributed to local vibrational modes of nitrogen dimers on Ga- and As-lattice sites. Rapid thermal annealing under appropriate conditions is found to be able to remove the nitrogen dimers. The required minimum annealing temperature coincides with the threshold-like onset of strong, near-band-gap photoluminescence. This finding suggests that the nitrogen dimers are connected with nonradiative recombination centers. © 2004 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
71.20.Nr Semiconductor compounds
61.72.J- Point defects and defect clusters
78.55.Cr III-V semiconductors

Role of fluorine in suppressing boron transient enhanced diffusion in preamorphized Si

G. Impellizzeri, J. H. R. dos Santos, S. Mirabella, F. Priolo, E. Napolitani, and A. Carnera

Appl. Phys. Lett. 84, 1862 (2004); http://dx.doi.org/10.1063/1.1675935 (3 pages) | Cited 34 times

Online Publication Date: 10 March 2004

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We have explained the role of fluorine in the reduction of the self-interstitial population in a preamorphized Si layer under thermal treatment. For this purpose, we have employed a B spike layer grown by molecular-beam epitaxy as a marker for the self-interstitial local concentration. The amorphized samples were implanted with 7×1012, 7×1013, or 4×1014 F/cm2 at 100 keV, and afterwards recrystallized by solid phase epitaxy. Thermal anneals at 750 or 850 °C were performed in order to induce the release of self-interstitials from the end-of-range (EOR) defects and thus provoke the transient enhanced diffusion of B atoms. We have shown that the incorporation of F reduces the B enhanced diffusion in a controlled way, up to its complete suppression. It is seen that no direct interaction between B and F occurs, whereas the suppression of B enhanced diffusion is related to the F ability in reducing the excess of silicon self-interstitials emitted by the EOR source. These results are reported and discussed. © 2004 American Institute of Physics.
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61.72.J- Point defects and defect clusters
66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing

Reflectance anisotropy of Gd5Si2Ge2 and Tb5Si2.2Ge1.8

S. J. Lee, J. M. Park, J. E. Snyder, D. C. Jiles, D. L. Schlagel, T. A. Lograsso, A. O. Pecharsky, and D. W. Lynch

Appl. Phys. Lett. 84, 1865 (2004); http://dx.doi.org/10.1063/1.1687463 (3 pages) | Cited 5 times

Online Publication Date: 10 March 2004

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Reflectance difference (RD) spectra for the a–b plane of the single crystals of Gd5Si2Ge2 and b–c planes of Gd5Si2Ge2 and Tb5Si2.2Ge1.8 were obtained in the photon energy range of 1.5–5.5 eV. Several peaks were observed for these crystals in the measured spectrum range. Similar features were observed in the RD spectra for the b–c planes of Gd5Si2Ge2 and Tb5Si2.2Ge1.8, while different features were observed for the a–b plane and b–c plane of Gd5Si2Ge2. The RD spectra for the crystals arise not only from the surface anisotropy but also from the bulk anisotropy due to the monoclinic structure of the bulk crystal. © 2004 American Institute of Physics.
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61.66.Dk Alloys
73.20.At Surface states, band structure, electron density of states
71.15.-m Methods of electronic structure calculations
78.40.Kc Metals, semimetals, and alloys

Long wavelength emission in InxGa1−xAs quantum dot structures grown in a GaAs barrier by metalorganic chemical vapor deposition

A. Passaseo, V. Tasco, M. De Giorgi, M. T. Todaro, M. De Vittorio, and R. Cingolani

Appl. Phys. Lett. 84, 1868 (2004); http://dx.doi.org/10.1063/1.1652255 (3 pages) | Cited 8 times

Online Publication Date: 10 March 2004

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We demonstrate a method to obtain room temperature long wavelength emission from InGaAs quantum dots (QDs) growth directly into a binary GaAs matrix. The wavelength is tuned from 1.26 up to 1.33 μm by varying the V/III ratio during growth of the GaAs cap layer, without using a seeding layer or InGaAs wells. Strong improvement in terms of line-shape narrowing and efficiency is obtained. In addition to the shift in wavelength we observe an impressive reduction of temperature dependent quenching of the emission efficiency, which decreases only by a factor of 3 between cryogenic temperatures and room temperature, very good for QD structures emitting at 1.3 μm. Photoluminescence spectroscopy and theoretical modeling were combined for interpretation of the results. © 2004 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.40.Gh Other heat and thermomechanical treatments

Pressure effect of glass transition temperature in Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk metallic glass

J. Z. Jiang, W. Roseker, M. Sikorski, Q. P. Cao, and F. Xu

Appl. Phys. Lett. 84, 1871 (2004); http://dx.doi.org/10.1063/1.1675937 (3 pages) | Cited 18 times

Online Publication Date: 10 March 2004

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Pressure effects on glass transition temperature and supercooled liquid region of a Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass have been investigated by performing in situ high-temperature and high-pressure x-ray powder diffraction measurements using synchrotron radiation. The glass transition was detected from the change of the slope of peak position as a function of temperature. It is found that the glass transition temperature increases with pressure by 4.4 K/GPa for the Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass, and the supercooled liquid range decreases with pressure by 2.9 K/GPa in a pressure range of 0–2.2 GPa. This method opens a possibility to study the pressure effect of glass transition process in glassy systems under high pressures (>1 GPa). © 2004 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses

Type I to type II transition at the interface between random and ordered domains of AlxGa1−xN alloys

S. V. Dudiy and Alex Zunger

Appl. Phys. Lett. 84, 1874 (2004); http://dx.doi.org/10.1063/1.1687464 (3 pages) | Cited 7 times

Online Publication Date: 10 March 2004

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We analyze the optical and transport consequences of the existence of ordered and random domains in partially ordered samples of AlxGa1−xN alloys. Using atomistic empirical pseudopotential simulations, we find that the band alignment between random and ordered domains changes from type I to type II at x ≃ 0.4. This leads to an increase by two to three orders of magnitude in the radiative lifetime of the electron–hole recombination. This can explain the experimentally observed mobility-lifetime product behaviors with changing Al concentration. The type I to type II transition results from a competition between the ordering-induced band folding effect and hole confinement on Ga-rich monolayers within the ordered structure. © 2004 American Institute of Physics.
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71.20.Nr Semiconductor compounds
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Formation of ultrahigh-density InAs/AlAs quantum dots by metalorganic chemical vapor deposition

Se-Ki Park, Jun Tatebayashi, and Yasuhiko Arakawa

Appl. Phys. Lett. 84, 1877 (2004); http://dx.doi.org/10.1063/1.1687465 (3 pages) | Cited 3 times

Online Publication Date: 10 March 2004

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High-density InAs quantum dots (QDs) were grown on an AlAs matrix layer by metalorganic chemical vapor deposition. The effects of various growth parameters were systematically studied by atomic force microscopy. The AlAs layer was essential for obtaining high-density QDs, with densities as high as 4.7×1011 cm−2. We have also demonstrated the effects of a thin GaAs insertion layer to prevent aluminum intermixing and to block some defects, which occurred on the GaAs buffer layer. As a result, the photoluminescence intensity of InAs/GaAs/AlAs QD structures was improved by two orders of magnitude. © 2004 American Institute of Physics.
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78.67.Hc Quantum dots
81.07.Ta Quantum dots
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
68.55.-a Thin film structure and morphology
68.37.Ps Atomic force microscopy (AFM)
82.30.Nr Association, addition, insertion, cluster formation

Reduced photorefraction in hafnium-doped single-domain and periodically poled lithium niobate crystals

Edvard P. Kokanyan, Luca Razzari, Ilaria Cristiani, Vittorio Degiorgio, and John B. Gruber

Appl. Phys. Lett. 84, 1880 (2004); http://dx.doi.org/10.1063/1.1687460 (3 pages) | Cited 45 times

Online Publication Date: 10 March 2004

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Transient and steady-state measurements of photoinduced birefringence in single-domain and periodically poled lithium niobate (LN) crystals containing different nonphotorefractive impurities are presented. The birefringence change is induced by a 532 nm beam and probed by a 633 nm beam. Data were taken at 25 and 50 °C. We find that doping by HfO2 is very effective in reducing the photorefraction. This is interesting also because it is known that hafnium-doped LN crystals can be periodically poled during growth. The analysis of the rise and decay of the induced birefringence shows that doping considerably increases both the photoconductivity and the dark conductivity of the LN crystals. © 2004 American Institute of Physics.
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78.20.Fm Birefringence
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
72.40.+w Photoconduction and photovoltaic effects
61.72.S- Impurities in crystals

Thermal conductivity of nanoporous bismuth thin films

D. W. Song, W.-N. Shen, B. Dunn, C. D. Moore, M. S. Goorsky, T. Radetic, R. Gronsky, and G. Chen

Appl. Phys. Lett. 84, 1883 (2004); http://dx.doi.org/10.1063/1.1682679 (3 pages) | Cited 31 times

Online Publication Date: 10 March 2004

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The thermal conductivity of nanoporous Bi thin films has been experimentally determined. Samples are fabricated by a liquid phase deposition, and their thermal conductivities are measured by a differential 3ω method. Nanoporous Bi thin films exhibit an order-of-magnitude reduction in thermal conductivity compared to that of solid films, most likely the result of a reduction in phonon mean free path. When porous Bi films are exposed to a hydrogen plasma, thermal conductivity measurements reveal no variation with extent of porosity, while electrical conductivity is much more sensitive to porosity, suggesting the possibility of independent control of these two intrinsic properties. © 2004 American Institute of Physics.
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81.05.Rm Porous materials; granular materials
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ng Insulators

Investigations of V-shaped defects and photoluminescence of thin GaN-rich GaNP layers grown on a GaN epilayer by metalorganic chemical vapor deposition

H. D. Li, M. Tsukihara, Y. Naoi, Y. B. Lee, and S. Sakai

Appl. Phys. Lett. 84, 1886 (2004); http://dx.doi.org/10.1063/1.1687462 (3 pages) | Cited 1 time

Online Publication Date: 10 March 2004

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Structural defects in high-temperature GaN-rich GaNP layers grown on a thick GaN epilayer by metalorganic chemical vapor deposition were investigated by means of transmission electron microscopy and atomic force microscopy. It is found that there are inverted hexagonal pyramid V-shaped defects in the GaNP layers with a higher phosphorus (P) composition. These defects are generally related to threading dislocations propagating from the GaN layer beneath. Consequently, the dislocation density in the GaNP layers is dramatically decreased to 5–8×107 cm−2. Photonluminescence (PL) measurements show that the PL wavelength of GaNP redshifts and the integrated emission intensity significantly increases, with respect to that from GaN layers grown under identical conditions. The emission enhancement is attributed to lowering of the dislocation density and enlarging the escape cone of photons by the rough surface, which result from the V-shaped defects formed in the GaNP layer. © 2004 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.Ct Interface structure and roughness
68.37.Ps Atomic force microscopy (AFM)

“Umbrella”-like precipitates in nitrogen-doped Czochralski silicon wafers

A. Kvit, A. Karoui, G. Duscher, and G. A. Rozgonyi

Appl. Phys. Lett. 84, 1889 (2004); http://dx.doi.org/10.1063/1.1669069 (3 pages)

Online Publication Date: 10 March 2004

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Show Abstract
Nitrogen effect on nucleation of oxygen precipitates in Czochralski Si has been investigated by transmission electron microscopy, Z-contrast imaging, and electron energy loss spectrometry (EELS). We have examined unusual “umbrella” shape oxygen precipitates in bulk of ingot in depths of more than 40 μm. Two predominant orientations of “umbrella” have been found along [110] and [−1−10] directions. We have investigated the distribution of nitrogen, oxygen, and interstitial Si by EELS profile taken simultaneously with HR Z-contrast image. The mechanism of nitrogen-enriched oxygen precipitates nucleation has been discussed. © 2004 American Institute of Physics.
Show PACS
81.30.Mh Solid-phase precipitation
61.72.J- Point defects and defect clusters
61.72.S- Impurities in crystals
61.72.uf Ge and Si
79.20.Uv Electron energy loss spectroscopy
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