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20 May 2002

Volume 80, Issue 20, pp. 3667-3864

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Nonlinear photonic band-gap structure with extremely high efficiency for third-harmonic generation

B. Shi and X. Wang

Appl. Phys. Lett. 80, 3667 (2002); http://dx.doi.org/10.1063/1.1480120 (3 pages) | Cited 4 times

Online Publication Date: 13 May 2002

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A method of tailoring the electromagnetic states in photonic band-gap structures was used in designing a dielectric structure optimized for third-harmonic generation. The structure we considered was a stack of several kinds of χ(2) nonlinear bilayers approximately 10 μm in length. In the theoretical analysis and numerical experiment, a conversion efficiency enhancement of more than 14 orders of magnitude, as compared with that in a normal conventional setup of two crystals, was found. The possibility of efficient third-harmonic generation in a single structure of χ(2) materials and the phenomenal enhancement of the conversion efficiency show that the electromagnetic state control in photonic band-gap structures offers great potential in nonlinear optics. © 2002 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
42.70.Mp Nonlinear optical crystals
42.50.-p Quantum optics
42.79.Wc Optical coatings

Thick, crack-free blue light-emitting diodes on Si(111) using low-temperature AlN interlayers and in situ SixNy masking

A. Dadgar, M. Poschenrieder, J. Bläsing, K. Fehse, A. Diez, and A. Krost

Appl. Phys. Lett. 80, 3670 (2002); http://dx.doi.org/10.1063/1.1479455 (3 pages) | Cited 58 times

Online Publication Date: 13 May 2002

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Thick, entirely crack-free GaN-based light-emitting diode structures on 2 in. Si(111) substrates were grown by metalorganic chemical-vapor deposition. The ∼2.8-μm-thick diode structure was grown using a low-temperature AlN:Si seed layer and two low-temperature AlN:Si interlayers for stress reduction. In current–voltage measurements, low turn-on voltages and a series resistance of 55 Ω were observed for a vertically contacted diode. By in situ insertion of a SixNy mask, the luminescence intensity is significantly enhanced. A light output power of 152 μW at a current of 20 mA and a wavelength of 455 nm is achieved. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.40.Hp Lithography, masks and pattern transfer
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.60.Bs Mechanical and acoustical properties
85.30.De Semiconductor-device characterization, design, and modeling

Three-dimensional focal spots related to two-photon excitation

Hong-Bo Sun, Tomokazu Tanaka, and Satoshi Kawata

Appl. Phys. Lett. 80, 3673 (2002); http://dx.doi.org/10.1063/1.1478128 (3 pages) | Cited 58 times

Online Publication Date: 13 May 2002

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We used a photopolymer consisting of urethane acrylate monomer and free-radical-type initiators as a media for recording two-photon-excited (TPE) focal spots in three dimensions. Mathematically, the initiator plays a role of kmath operator, transforming the quadratic light intensity distribution to a linear radical concentration distribution. Then, the monomer acts as a three-dimensional (3D) “film,” fixing the focal volume where radical concentration is above a threshold as a voxel. An ascending scan method was utilized to avoid substrate truncation and to achieve isolated complete 3D voxels, from which accurate forms of TPE focus were obtained. The 3D photographing technology led to a clear explanation of the origin of pronounced contradictions in reported spatial resolutions, and would be critical for laser precision microfabrication in various materials. © 2002 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
42.70.Jk Polymers and organics
42.70.Gi Light-sensitive materials

Tuning characteristics of InAsSb continuous-wave lasers

V. Sherstnev, A. Krier, A. Popov, and P. Werle

Appl. Phys. Lett. 80, 3676 (2002); http://dx.doi.org/10.1063/1.1478147 (3 pages)

Online Publication Date: 13 May 2002

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We present a detailed analysis of the tuning characteristics of InAsSb continuous-wave (cw) single-frequency lasers emitting at 3.3 μm (3050 cm−1). The lasers demonstrate a tuning range of −7.5 cm−1 by changing the current and −3.5 cm−1 by changing the heat sink temperature without mode hopping. The tuning rates are of −0.015 to −0.089 cm−1/mA and −0.11 to 0.27 cm−1/K. The laser tunes to the blue side both with increasing injection current and heat sink temperature. The extended tuning is attributed to the carrier heating effect in the cw operation and the band-filling effect in the presence of strong losses. © 2002 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes

Extraordinary transmission of organic photoluminescence through an otherwise opaque metal layer via surface plasmon cross coupling

Dawn K. Gifford and Dennis G. Hall

Appl. Phys. Lett. 80, 3679 (2002); http://dx.doi.org/10.1063/1.1478776 (3 pages) | Cited 37 times

Online Publication Date: 13 May 2002

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We report extraordinary transmission of organic photoluminescence through an otherwise opaque, thin metal layer. We observe strong, angularly dependent photoluminescence from silver-coated films of Alq3 deposited on a corrugated substrate. Experimental and theoretical analysis indicates that light passes through the silver layer by cross coupling between surface plasmons on opposite sides of that layer. At narrow angles, the observed photoluminescence intensity is up to 10 times greater than that from a nonsilver-coated, uncorrugated organic film. This suggests an alternate device structure for efficient organic light emitting diodes. © 2002 American Institute of Physics.
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78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds
78.66.Bz Metals and metallic alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
85.60.Jb Light-emitting devices

AlGaInN-based ultraviolet light-emitting diodes grown on Si(111)

G. Kipshidze, V. Kuryatkov, B. Borisov, M. Holtz, S. Nikishin, and H. Temkin

Appl. Phys. Lett. 80, 3682 (2002); http://dx.doi.org/10.1063/1.1480886 (3 pages) | Cited 32 times

Online Publication Date: 13 May 2002

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Ultraviolet light-emitting diodes grown on Si(111) by gas-source molecular-beam epitaxy with ammonia are described. The layers are composed of superlattices of AlGaN/GaN and AlN/AlGaInN. The layers are doped n and p type with Si and Mg, respectively. Hole concentration of 4×1017 cm−3, with a mobility of 8 cm2/Vs, is measured in Al0.4Ga0.6N/GaN. We demonstrate effective n- and p-type doping of structures based on AlN/AlGaInN. Light-emitting diodes based on these structures show light emission between 290 and 334 nm. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Dn Low-field transport and mobility; piezoresistance

Nondiffracting periodically space-variant polarization beams with subwavelength gratings

Ze’ev Bomzon, Avi Niv, Gabriel Biener, Vladimir Kleiner, and Erez Hasman

Appl. Phys. Lett. 80, 3685 (2002); http://dx.doi.org/10.1063/1.1480477 (3 pages) | Cited 2 times

Online Publication Date: 13 May 2002

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A class of propagation-invariant vector fields with uniform intensity and periodically space-varying polarization is presented. The beams were formed using computer-generated space-variant subwavelength gratings. A theoretical analysis as well as experimental results using gratings designed for CO2 laser radiation at a wavelength of 10.6 μm is discussed. © 2002 American Institute of Physics.
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42.79.Dj Gratings
42.25.Ja Polarization
42.79.Ci Filters, zone plates, and polarizers
42.25.Gy Edge and boundary effects; reflection and refraction

Direct measurement of the fine-structure interval in alkali atoms using diode lasers

Ayan Banerjee, Umakant D. Rapol, and Vasant Natarajan

Appl. Phys. Lett. 80, 3688 (2002); http://dx.doi.org/10.1063/1.1480890 (3 pages) | Cited 1 time

Online Publication Date: 13 May 2002

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We demonstrate a technique for directly measuring the fine-structure interval in alkali atoms using two frequency-stabilized diode lasers. Each laser has a linewidth of order 1 MHz and precise tunability: one laser is tuned to a hyperfine transition in the D1 line, and the other laser to a hyperfine transition in the D2 line. The outputs of the lasers are fed into a scanning Michelson interferometer that measures the ratio of their wavelengths accurately. To illustrate the technique, we measure the fine-structure interval in Rb, and obtain a value of 237.6000(3)(5) cm−1 for the hyperfine-free 5P3/2–5P1/2 interval. © 2002 American Institute of Physics.
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32.30.Rj X-ray spectra
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
07.60.Ly Interferometers
31.30.Gs Hyperfine interactions and isotope effects

Long wavelength (15 and 23 μm) GaAs/AlGaAs quantum cascade lasers

Jochen Ulrich, Johann Kreuter, Werner Schrenk, Gottfried Strasser, and Karl Unterrainer

Appl. Phys. Lett. 80, 3691 (2002); http://dx.doi.org/10.1063/1.1481236 (3 pages) | Cited 8 times

Online Publication Date: 13 May 2002

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Quantum cascade lasers based on GaAs/AlGaAs chirped superlattice active regions have been achieved at wavelengths of 15 and 23 μm. In pulsed mode they operate up to temperatures of 220 and 100 K, respectively. While the 15 μm-laser employs a standard waveguide with n+-doped cladding, the 23 μm-laser was made with a metallic surface plasmon waveguide. The threshold current densities at cryogenic temperatures of 2.2 kA/cm2 (15 μm) and 10.2 kA/cm2 (23 μm) reflect the differences in intersubband lifetimes and waveguide losses close to the reststrahlenband. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
81.05.Ea III-V semiconductors
81.07.St Quantum wells
78.67.De Quantum wells
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Fg Quantum wells
73.21.Cd Superlattices
42.79.Gn Optical waveguides and couplers

Spectral method for the simultaneous determination of uncorrelated and correlated amplitude and timing jitter

Michael C. Gross, Marc Hanna, Ketan M. Patel, and Stephen E. Ralph

Appl. Phys. Lett. 80, 3694 (2002); http://dx.doi.org/10.1063/1.1480105 (3 pages) | Cited 5 times

Online Publication Date: 13 May 2002

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We present a technique for simultaneous determination of the uncorrelated and correlated timing and amplitude jitter of a pulse train from its radio-frequency spectrum. First, we present a robust analysis that separately identifies both correlated and uncorrelated jitter. Second, we show that all four noise components can be uniquely determined by combining the traditional integrating calculation with a nonintegrating computation. We present simulation results that confirm the accuracy of this technique. © 2002 American Institute of Physics.
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02.70.Hm Spectral methods
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
02.60.Jh Numerical differentiation and integration

Effective laser ultrasonic detection with biased GaAs photoelectromotive force detectors

J. Castillo, P. Rodriguez, A. Aguirre, S. Stepanov, and S. Mansurova

Appl. Phys. Lett. 80, 3697 (2002); http://dx.doi.org/10.1063/1.1479201 (3 pages) | Cited 2 times

Online Publication Date: 13 May 2002

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Improvement of the sensitivity of laser-induced ultrasonic detection by GaAs adaptive photoelectromotive force (photo-EMF) devices under external dc bias is reported. The gain in responsivity of the detector about 7× in ≈10 MHz frequency band was observed under application of an external dc field ≈50 V/mm at λ = 633 nm. Detailed experiments show that this growth is paid by proportional shift of maximum of the photo-EMF response to lower spatial frequencies and by appearance of a relatively broad resonance pick located at modulation frequencies lower than the cutoff frequency of the unbiased GaAs photo-EMF detector. These results are consistently interpreted using a theoretical model of the photo-EMF effect in bipolar photoconductor with large lifetime of one type of the photocarriers. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
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Effects of cathode materials and arc current on optimal bias of a cathodic arc through a magnetic duct

Tao Zhang, Paul K. Chu, and Ian G. Brown

Appl. Phys. Lett. 80, 3700 (2002); http://dx.doi.org/10.1063/1.1481235 (3 pages) | Cited 8 times

Online Publication Date: 13 May 2002

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A negatively biased collecting plate was used to collect the ion current of the cathodic arc plasma transported through a curved magnetic duct. The optimal duct bias at which the duct has the maximum efficiency for plasma transport was measured for C, Ti, Mo, and W plasmas as a function of the arc current and guiding magnetic field. The optimal bias decreased with the magnetic field and was almost steady when the field was above 400 G. The optimal bias at 400 G and above increased with the arc current for C plasma but the opposite relationship was observed for Ti, Mo, and W plasmas. The effects of the plasma density, ion mass, ion kinetic energy, and magnetic field on the optimal bias are discussed. © 2002 American Institute of Physics.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.25.Fi Transport properties
52.50.Nr Plasma heating by DC fields; ohmic heating, arcs
52.55.Tn Ideal and resistive MHD modes; kinetic modes

Study on velocity spread for axis-encircling electron beams generated by single magnetic cusp

S. G. Jeon, C. W. Baik, D. H. Kim, G. S. Park, N. Sato, and K. Yokoo

Appl. Phys. Lett. 80, 3703 (2002); http://dx.doi.org/10.1063/1.1480468 (3 pages) | Cited 6 times

Online Publication Date: 13 May 2002

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The physical characteristics of an annular Pierce-type electron gun are investigated analytically. The electron gun is used in conjunction with a nonadiabatic magnetic reversal and adiabatic compression region to produce an axis-encircling beam. Typical magnetic field profiles that can generate zero velocity spreads are obtained from the analytical calculation, taking into account initial canonical angular momentum spreads at the cathode and the crossing of the beam trajectory and magnetic flux line before the magnetic cusp. Using this magnetic fields, a fairly low axial velocity spread of less than 1% is achieved by an electron trajectory program [W. B. Hermannsfeldt, Electron Trajectory Program (Stanford Linear Acceleration Center, Stanford, CA, 1979)], which agrees well with that by analytical estimation. © 2002 American Institute of Physics.
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41.75.Fr Electron and positron beams
41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
07.77.Ka Charged-particle beam sources and detectors
29.27.Eg Beam handling; beam transport
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Observation of dopant-mediated intermixing at Ge/Si Interface

Hideki Takeuchi, Pushkar Ranade, Vivek Subramanian, and Tsu-Jae King

Appl. Phys. Lett. 80, 3706 (2002); http://dx.doi.org/10.1063/1.1480485 (3 pages) | Cited 5 times

Online Publication Date: 13 May 2002

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Rapid intermixing of Ge deposited onto a Si substrate during 900 °C rapid thermal annealing was analyzed using secondary ion mass spectroscopy. In undoped Ge samples, a 50 nm thick graded Si1−xGex layer was formed in 1 min, consuming 30 nm Ge and 20 nm Si. Negligible profile change was seen after an additional 1 min anneal. With dopants inside the deposited Ge layer, the extent of the intermixing is increased: For B doping, 30 nm Ge and 30 nm Si are consumed; for As doping, 5 nm Ge and 100 nm Si are consumed. In the case of B, Ge–B codiffusion from the Si1−xGex/Si heterojunction edge was also observed. The p-n junction depth difference between the two dopants can be explained by the difference in their solubilities, while the Ge–B codiffusion is attributed to excess vacancies generated during the initial intermixing. © 2002 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.Cc Kinetics of defect formation and annealing
61.82.Fk Semiconductors
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.72.J- Point defects and defect clusters

Phosphorus-doped silicon nanowires studied by near edge x-ray absorption fine structure spectroscopy

Y. H. Tang, T. K. Sham, A. Jürgensen, Y. F. Hu, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 80, 3709 (2002); http://dx.doi.org/10.1063/1.1478796 (3 pages) | Cited 10 times

Online Publication Date: 13 May 2002

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The electronic structure and chemical bonding of heavily phosphorus-doped silicon nanowires have been investigated by near edge x-ray absorption fine structure spectroscopy using total electron yield and x-ray fluorescence yield. The results show that the wires are encapsulated within a silicon oxide layer and that the core of the nanowires was crystalline silicon doped with phosphorus. Phosphorus is found to be inside the core of the Si wire as well as at the silicon oxide–core silicon wire interface but not on the surface of the as-prepared nanowire. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.07.Vb Quantum wires
78.70.Dm X-ray absorption spectra
71.20.Mq Elemental semiconductors
71.55.Cn Elemental semiconductors
81.05.Cy Elemental semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems

Low-energy ion-induced tensile stress of self-assembled alkanethiol monolayers

A. N. Itakura, R. Berger, T. Narushima, and M. Kitajima

Appl. Phys. Lett. 80, 3712 (2002); http://dx.doi.org/10.1063/1.1478153 (3 pages) | Cited 3 times

Online Publication Date: 13 May 2002

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Monolayers of alkanethiols on gold have been exposed to low energy Ar ion. A micromechanical cantilever sensor technique was used to determine in situ the influence of the ion dose on the surface stress in the monolayers. In contrast to compressive surface stress during self-assembled monolayer growth, a strong tensile surface stress of about −0.7 N/m was found when the sensor is exposed to Ar ions. This value is 3–4 times larger than the compressive surface stress. We attribute this stress to a reaction between the alkyl chains in the molecules of the alkanethiol monolayer. © 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
61.80.Jh Ion radiation effects
61.82.Pv Polymers, organic compounds

Increased transmission of a thin gold film by adsorbed layers of dye molecules

Ulrich C. Fischer, Eugene Bortchagovsky, Jörg Heimel, and René T. Hanke

Appl. Phys. Lett. 80, 3715 (2002); http://dx.doi.org/10.1063/1.1480471 (3 pages) | Cited 4 times

Online Publication Date: 13 May 2002

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Thin multilayers of a negatively charged cyanine dye and a positively charged polyelectrolyte were deposited onto a thin, partially transparent film of gold, initially covered by a self-assembled monolayer of cystamine. Transmission spectra of the multilayers have an antisymmetric shape with a dip and a peak in the transmission. Unlike the transmission spectra of the same dye on a transparent glass support, the spectra reflect the shape of the real part of the dielectric function of the dye layer. At the peak the transmission exceeds the transmission of the uncovered gold film by a factor of up to 2.5. © 2002 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.40.Me Organic compounds and polymers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Low-etch-pit-density GaN substrates by regrowth on free-standing GaN films

Chiung-Chi Tsai, Chen-Shiung Chang, and Tsung-Yu Chen

Appl. Phys. Lett. 80, 3718 (2002); http://dx.doi.org/10.1063/1.1480108 (3 pages) | Cited 5 times

Online Publication Date: 13 May 2002

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In this study, GaN substrates with low-density etch pits were obtained by regrowth on free-standing GaN films (two steps) by hydride vapor-phase epitaxy (HVPE). The etch-pit density was lower than 4×104 cm−2 by atomic-force microscopy. The density is significantly lower than that of the HVPE-grown (one-step) GaN films (HVPE GaN), using sapphire as a substrate. The optical and electrical properties of the two-step HVPE-grown GaN substrates are superior to those of HVPE GaN. Temperature-dependent photoluminescence measurements reveal that thermal quenching behavior of the 2.9 eV band is possibly attributed to a shallow acceptor level at about 118±5 meV above the valence band. © 2002 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
71.20.Nr Semiconductor compounds
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
68.37.Ps Atomic force microscopy (AFM)

Dynamics of twisted nematic liquid crystal pi-cells

Shu-Hsia Chen and Chiu-Lien Yang

Appl. Phys. Lett. 80, 3721 (2002); http://dx.doi.org/10.1063/1.1480880 (3 pages) | Cited 19 times

Online Publication Date: 13 May 2002

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A twisted nematic liquid crystal pi-cell with fast optical response time of 2.2 ms was prepared. We investigated the dynamics of this cell and observed the back-flow-induced optical overshoot phenomena both in homeotropic-to-planar state transition and planar-to-homeotropic state transition. We analyzed the behavior of the director and found that there is a tip-over phenomenon when the field is removed from relatively high voltage (>6 V). More important, the fluid flow effect results in the reverse twist both in the rising process and the decay process. Consequently, the reverse twist increases and decreases the effective phase retardation on the optical rising and decay process, respectively, and thus speeds up the optical response in both stages. © 2002 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.70.Df Liquid crystals
64.70.M- Transitions in liquid crystals

High spatial resolution grain orientation and strain mapping in thin films using polychromatic submicron x-ray diffraction

N. Tamura, A. A. MacDowell, R. S. Celestre, H. A. Padmore, B. Valek, J. C. Bravman, R. Spolenak, W. L. Brown, T. Marieb, H. Fujimoto, B. W. Batterman, and J. R. Patel

Appl. Phys. Lett. 80, 3724 (2002); http://dx.doi.org/10.1063/1.1477621 (3 pages) | Cited 39 times

Online Publication Date: 13 May 2002

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The availability of high brilliance synchrotron sources, coupled with recent progress in achromatic focusing optics and large area two-dimensional detector technology, has allowed us to develop an x-ray synchrotron technique that is capable of mapping orientation and strain/stress in polycrystalline thin films with submicron spatial resolution. To demonstrate the capabilities of this instrument, we have employed it to study the microstructure of aluminum thin film structures at the granular and subgranular levels. Due to the relatively low absorption of x-rays in materials, this technique can be used to study passivated samples, an important advantage over most electron probes given the very different mechanical behavior of buried and unpassivated materials. © 2002 American Institute of Physics.
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61.05.cp X-ray diffraction
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Projecting picosecond lattice dynamics through x-ray topography

O. Synnergren, M. Harbst, T. Missalla, J. Larssona), G. Katona, R. Neutze, and R. Wouts

Appl. Phys. Lett. 80, 3727 (2002); http://dx.doi.org/10.1063/1.1476957 (3 pages) | Cited 7 times

Online Publication Date: 13 May 2002

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A method for time-resolved x-ray diffraction studies has been demonstrated. As a test case, coherent acoustic phonon propagation into crystalline InSb is observed using a laser plasma x-ray source. An extended x-ray topogram of the semiconductor’s surface was projected onto a high spatial resolution x-ray detector and acoustic phonons were excited by rapidly heating the crystal’s surface with a femtosecond laser pulse. A correlation between the spatial position on the x-ray detector and the time of arrival of the laser pulse was encoded into the experimental geometry by tilting the incident laser pulse with an optical grating. This approach enabled a temporal window of 200 ps to be sampled in a single topogram, thereby negating the disadvantages of pulse-to-pulse fluctuations in the intensity and spectrum of the laser-plasma source. © 2002 American Institute of Physics.
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68.37.Yz X-ray microscopy
78.47.-p Spectroscopy of solid state dynamics
63.20.-e Phonons in crystal lattices
68.35.Ja Surface and interface dynamics and vibrations

Luminescence mechanisms in quaternary AlxInyGa1−x−yN materials

Mee-Yi Ryu, C. Q. Chen, E. Kuokstis, J. W. Yang, G. Simin, and M. Asif Khan

Appl. Phys. Lett. 80, 3730 (2002); http://dx.doi.org/10.1063/1.1481766 (3 pages) | Cited 17 times

Online Publication Date: 13 May 2002

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Low-temperature photoluminescence investigations have been carried out in the quaternary AlInGaN epilayers and AlInGaN/AlInGaN multiple quantum wells (MQWs) grown by pulsed metalorganic chemical-vapor deposition (PMOCVD). With increasing excitation power density, the emission peaks in both AlInGaN epilayers and MQWs show a strong blueshift and their linewidths increase. The luminescence of the samples grown by PMOCVD is attributed to recombination of carriers/excitons localized at band-tail states. We also demonstrate the luminescence properties of AlInGaN and AlGaN materials grown by a pulsed atomic-layer epitaxy and conventional MOCVD, respectively. © 2002 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.67.De Quantum wells
71.35.Gg Exciton-mediated interactions
81.07.St Quantum wells
73.21.Fg Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Origin of strong G′ band in Raman spectra of carbon whiskers

Jian Dong, Wanci Shen, and Bruce Tatarchuk

Appl. Phys. Lett. 80, 3733 (2002); http://dx.doi.org/10.1063/1.1481783 (3 pages) | Cited 5 times

Online Publication Date: 13 May 2002

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Raman scattering has been studied on one kind of carbon whiskers. The G′ band, overtone of D band, is the most intense of all bands—its intensity is up to ten times stronger than that of the G band. Such phenomena can be observed with different excitation wavelength. The strong intensity of the G′ band may be related to the disclination existing in the whiskers. Polarized Raman spectra are obtained from the edge plane of the whiskers. The intensity of G′ bands obtained with polarized light parallel to carbon layers (E⊥c) is ten times as strong as that with polarized light normal to carbon layers (E∥c). © 2002 American Institute of Physics.
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78.30.Na Fullerenes and related materials
81.05.U- Carbon/carbon-based materials
78.66.Tr Fullerenes and related materials
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
61.72.Lk Linear defects: dislocations, disclinations

Strain maps at the atomic scale below Ge pyramids and domes on a Si substrate

P. Raiteri, Leo Miglio, F. Valentinotti, and M. Celino

Appl. Phys. Lett. 80, 3736 (2002); http://dx.doi.org/10.1063/1.1475775 (3 pages) | Cited 22 times

Online Publication Date: 13 May 2002

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In this letter, the strain field below uncapped Ge islands of a different shape on a Si(001) substrate is estimated by molecular dynamics simulations at a realistic scale. Comparison to the Fourier transform maps of transmission electron micrographs, recently reported in literature, shows a very good agreement. We point out that the complex deformation in silicon, just below the edges of the Ge islands, is far from being uniaxial. The stress distribution generated by such a strain determines the range of interdot repulsion. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
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Wet chemical nitridation of GaAs (100) by hydrazine solution for surface passivation

V. L. Berkovits, V. P. Ulin, M. Losurdo, P. Capezzuto, G. Bruno, G. Perna, and V. Capozzi

Appl. Phys. Lett. 80, 3739 (2002); http://dx.doi.org/10.1063/1.1479212 (3 pages) | Cited 18 times

Online Publication Date: 13 May 2002

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A mild wet nitridation procedure using hydrazine-based solutions has been developed for GaAs (100) surface passivation. Both x-ray photoelectron spectroscopy and spectroscopic ellipsometry show that this nitridation procedure results in a very thin, coherent, and homogeneous GaN layer that is very stable in air. Photoluminescence data show a strong enhancement of the intensity as compared to that of an as-cleaned GaAs sample, indicating that this nitrided layer provides both chemical and electronic passivation of GaAs surfaces. The chemical mechanism of nitridation is discussed. © 2002 American Institute of Physics.
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81.65.Rv Passivation
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.65.Cf Surface cleaning, etching, patterning
73.20.At Surface states, band structure, electron density of states
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
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