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13 Dec 2004

Volume 85, Issue 24, pp. 5819-6053

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 5968 (2004); http://dx.doi.org/10.1063/1.1830083 (3 pages)

A. Urbieta, P. Fernández, and J. Piqueras
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Visualization of second-order nonlinear layer in thermally poled fused silica glass

Honglin An, Simon Fleming, and Guy Cox

Appl. Phys. Lett. 85, 5819 (2004); http://dx.doi.org/10.1063/1.1835554 (3 pages) | Cited 22 times

Online Publication Date: 9 December 2004

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Second-harmonic microscopy has been applied to characterize the second-order nonlinear layer in fused silica plates thermally poled at 280 °C and 3.5 kV for different time intervals. The nonlinear layer is found only under the anode surface and to be ∼5 μm deep under the anode for a poling time of 30 min. Progression of this layer into the bulk glass with poling time is also characterized.
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42.70.Ce Glasses, quartz
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Optically switchable biphotonic photorefractive effect in dye-doped liquid crystal films

Mei-Ru Lee, Jyun-Ruei Wang, Chia-Rong Lee, and Andy Y.-G. Fuh

Appl. Phys. Lett. 85, 5822 (2004); http://dx.doi.org/10.1063/1.1836864 (3 pages) | Cited 13 times

Online Publication Date: 9 December 2004

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This study reports the optically swichable photorefractive (PR) effect induced in a biphotonic grating in the presence of an applied dc voltage, in an azo-dye-doped liquid crystal (LC) film. When one green light is switched on (off), the PR grating can be turned on (off) by irradiating an interference field generated by two linearly polarized red lights. Experimental results demonstrate that such a PR effect follows primarily from a biphotonic process, with two mechanisms—the generation of green light-induced space charges by trans–cis isomerization, and the suppression of the formation of space charges by the red light in cis–trans back isomerization. These mechanisms apply to the dark and bright fringes of the red interference field, respectively. A spatially inhomogeneous space-charge field is then established to modulate the orientation of LCs, forming the PR grating in the presence of a dc voltage. Strong coupling of the two red lights is observable and measured dynamically during the formation of the PR grating in this study.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.-k Nonlinear optics
42.70.Df Liquid crystals
78.20.-e Optical properties of bulk materials and thin films
82.30.Qt Isomerization and rearrangement
68.15.+e Liquid thin films
77.22.Jp Dielectric breakdown and space-charge effects

Room-temperature external cavity GaSb-based diode laser around 2.13 μm

U. H. Jacobs, K. Scholle, E. Heumann, G. Huber, M. Rattunde, and J. Wagner

Appl. Phys. Lett. 85, 5825 (2004); http://dx.doi.org/10.1063/1.1833561 (2 pages) | Cited 4 times

Online Publication Date: 9 December 2004

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We report on a grating-tuned room-temperature (AlGaIn)(AsSb) diode laser oscillating on a single external cavity mode in the wavelength region around 2.13 μm. A total tuning range of 43 nm with an optical output power of up to 14.7 mW was achieved with a linewidth less than 3.85 MHz.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking

Resonance enhanced THz generation in electro-optic polymers near the absorption maximum

Alexander M. Sinyukov, Megan R. Leahy, L. Michael Hayden, Marnie Haller, Jingdong Luo, Alex K-Y. Jen, and Larry R. Dalton

Appl. Phys. Lett. 85, 5827 (2004); http://dx.doi.org/10.1063/1.1835550 (3 pages) | Cited 32 times

Online Publication Date: 9 December 2004

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The electro-optic (EO) coefficient of an organic nonlinear material exhibits a sharp resonance near the absorption maximum of the material. Due to this resonance, we experimentally observe the amplitude of the THz field generated from a 3.1-μm-thick EO polymer composite to be larger than that emitted from a 1000-μm-thick crystal of ZnTe. This comparison allows us to estimate the resonance enhanced EO coefficient of the polymer composite to be over 1250 pm∕V at 800 nm.
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42.70.Jk Polymers and organics
78.20.Jq Electro-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.70.Gq Microwave and radio-frequency interactions

Capture and release of photonic images in a quantum well

J. Krauß, J. P. Kotthaus, A. Wixforth, M. Hanson, D. C. Driscoll, A. C. Gossard, D. Schuh, and M. Bichler

Appl. Phys. Lett. 85, 5830 (2004); http://dx.doi.org/10.1063/1.1830676 (3 pages) | Cited 15 times

Online Publication Date: 9 December 2004

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The capture of an optical image in the plane of a semiconductor quantum well and the subsequent re-emission of this image in the form of a two-dimensional photon flux is demonstrated. Spatially resolved storage of photonic signals in a two-dimensional lateral potential landscape of the quantum well is employed to imprint optical images in the form of trapped photogenerated charges into the solid. The lateral two-dimensional potential modulation leads to very long storage times by a deliberate spatial separation of photogenerated electron–hole pairs. Once the potential modulation is lifted, the initial optical information is restored and the photographed image is released in a flash of light.
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42.79.Vb Optical storage systems, optical disks
42.30.Lr Modulation and optical transfer functions
42.30.Va Image forming and processing
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
68.65.Fg Quantum wells

Surface plasmon polariton based modulators and switches operating at telecom wavelengths

Thomas Nikolajsen, Kristjan Leosson, and Sergey I. Bozhevolnyi

Appl. Phys. Lett. 85, 5833 (2004); http://dx.doi.org/10.1063/1.1835997 (3 pages) | Cited 219 times

Online Publication Date: 9 December 2004

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We report design, fabrication, and characterization of thermo-optic Mach–Zender interferometric modulators and directional-coupler switches whose operation utilizes the long-range surface-plasmon-polariton waveguiding along 15-nm-thin and 8-μm-wide gold stripes embedded in polymer and heated by electrical signal currents. The devices are characterized at the light wavelength of 1.55 μm, featuring low driving powers (<10 mW for modulators and <100 mW for switches), high extinction ratios (>30 dB), moderate response times (∼1 ms), and the total (fiber-to-fiber) insertion loss of ∼13 dB (for modulators) and ∼11 dB (for switches) when using single-mode fibers.
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42.79.Hp Optical processors, correlators, and modulators
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.81.Dp Propagation, scattering, and losses; solitons
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Medical image processing using transient Fourier holography in bacteriorhodopsin films

Sri-Rajasekhar Kothapalli, Pengfei Wu, Chandra S. Yelleswarapu, and D. V. G. L. N. Rao

Appl. Phys. Lett. 85, 5836 (2004); http://dx.doi.org/10.1063/1.1833567 (3 pages) | Cited 6 times

Online Publication Date: 9 December 2004

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Real time image processing is demonstrated by recording and reconstructing the transient photoisomerizative grating formed in the bR film using Fourier holography. Desired spatial frequencies including both high and low band in the object beam are reconstructed by controlling the reference beam intensity. The results are in agreement with a theoretical model based on photoisomerization grating. We exploit this technique to process mammograms in real-time for identification of microcalcifications buried in the soft tissue for early detection of breast cancer. A feature of the technique is the ability to transient display of selected spatial frequencies in the reconstructing process which enables the radiologists to study the features of interest.
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87.57.N- Image analysis
42.30.Va Image forming and processing
87.14.E- Proteins

Efficient second-harmonic generation of ultrafast pulses in periodically poled KNbO3

Nan Ei Yu, Sunao Kurimura, Kenji Kitamura, Oc-Yeub Jeon, Myoungsik Cha, Satoshi Ashihara, Takayuki Ohta, Tsutomu Shimura, Kazuo Kuroda, and Junji Hirohashi

Appl. Phys. Lett. 85, 5839 (2004); http://dx.doi.org/10.1063/1.1835557 (3 pages) | Cited 3 times

Online Publication Date: 9 December 2004

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Efficient second-harmonic generation of 95 fs pulses were achieved by simultaneous group-velocity matching and quasi-phase matching in a 10 mm long periodically poled potassium niobate crystal. The quasi-phase-matched bandwidth was 38 nm and second-harmonic pulse duration was 158 fs with a fundamental input pulse of 95 fs without spectral and temporal distortion in the S-band of telecommunication. Utilizing the larger off-diagonal nonlinear coefficient, d31 of potassium niobate, the conversion efficiency was significantly improved from that of periodically poled MgO-doped lithium niobate. [Appl. Phys. Lett. 82, 3388 (2003)]
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Low-threshold continuous-wave operation of quantum-cascade lasers grown by metalorganic vapor phase epitaxy

Mariano Troccoli, David Bour, Scott Corzine, Gloria Höfler, Ashish Tandon, Dan Mars, David J. Smith, Laurent Diehl, and Federico Capasso

Appl. Phys. Lett. 85, 5842 (2004); http://dx.doi.org/10.1063/1.1834715 (3 pages) | Cited 21 times

Online Publication Date: 9 December 2004

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We report on the realization of InGaAs∕InAlAs quantum-cascade lasers grown by metalorganic vapor phase epitaxy operating in continuous wave with low-threshold current densities at temperatures as high as 188 K. Threshold current densities of 950 A∕cm2 and output powers of 125 mW are measured at 80 K, while 3 mW of continuous output power are measured at 180 K, with a threshold of 2.5 kA∕cm2. In pulsed mode, peak output powers of more than 0.4 W were obtained at 80 K and of 160 mW at 300 K with thresholds of 700 A∕cm2 and 2.75 kA∕cm2, respectively.
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42.55.Px Semiconductor lasers; laser diodes
81.07.St Quantum wells
42.60.By Design of specific laser systems
81.05.Ea III-V semiconductors
68.65.Fg Quantum wells
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Passive mode locking of a mixed garnet Yb:Y3ScAl4O12 ceramic laser

Jiro Saikawa, Yoichi Sato, Takunori Taira, and Akio Ikesue

Appl. Phys. Lett. 85, 5845 (2004); http://dx.doi.org/10.1063/1.1836019 (3 pages) | Cited 8 times

Online Publication Date: 9 December 2004

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We have demonstrated a passively mode-locked Yb3+-doped Y3ScAl4O12 ceramic laser, which is a solid solution of Y3Al5O12 and Y3Sc2Al3O12, by using a semiconductor saturable-absorber mirror. The maximum average output power was as high as 150 mW with a pulse duration of 500 fs. With a 0.5% output coupler, pulses as short as 280 fs having an average output power of 62 mW at 1035.8 nm were obtained.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.Fc Modulation, tuning, and mode locking
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Tuning the exciton-photon coupling in a strongly coupled organic microcavity containing an optical wedge

Jakub Wenus, Liam G. Connolly, David M. Whittaker, Maurice S. Skolnick, and David G. Lidzey

Appl. Phys. Lett. 85, 5848 (2004); http://dx.doi.org/10.1063/1.1835556 (3 pages) | Cited 6 times

Online Publication Date: 9 December 2004

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We have fabricated strongly coupled organic microcavities by laminating an organic thin film between two dielectric mirrors. The organic film consisted of J aggregates of a cyanine dye suspended in a transparent matrix. By applying a nonuniform force across the substrate during lamination, the optical path length of the cavity changed linearly across the sample, thereby forming a wedge. This enabled cavity mode tuning by changing the position of the incident light beam with respect to the surface of the cavity. Transmission measurements are employed to investigate strong exciton-photon coupling in such microcavities. The results show a well-resolved anti-crossing behavior, which is confirmed by numerical analysis.
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78.66.Qn Polymers; organic compounds
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.55.Kz Solid organic materials
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Nearly attaining the theoretical efficiency of supersonic chemical oxygen-iodine lasers

V. Rybalkin, A. Katz, B. D. Barmashenko, and S. Rosenwaks

Appl. Phys. Lett. 85, 5851 (2004); http://dx.doi.org/10.1063/1.1836876 (3 pages) | Cited 10 times

Online Publication Date: 9 December 2004

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Improving the chemical efficiency of the supersonic chemical oxygen-iodine laser (COIL) is a key issue for the design of devices for both defense and industrial applications. Efficiencies around 30% for the supersonic COIL have been the state of the art in the last decade. Here, we report the achievement of a record (40%) for the chemical efficiency of the supersonic COIL. More specifically, we show that by carefully studying and optimizing the operation of the chemical generator, the mixing of heavy and light molecules in the gas phase and the optical extraction efficiency, we have approached the theoretical limit for the chemical efficiency.
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42.60.By Design of specific laser systems
42.55.Lt Gas lasers including excimer and metal-vapor lasers

Diffractionless propagation of light in a low-index photonic-crystal film

R. Iliew, C. Etrich, U. Peschel, F. Lederer, M. Augustin, H.-J. Fuchs, D. Schelle, E.-B. Kley, S. Nolte, and A. Tünnermann

Appl. Phys. Lett. 85, 5854 (2004); http://dx.doi.org/10.1063/1.1830675 (3 pages) | Cited 33 times

Online Publication Date: 9 December 2004

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We experimentally demonstrate diffractionless propagation of light over 12 diffraction lengths in a two-dimensional photonic crystal film made of silicon nitride (SiNx). We show that self-guided beams may propagate for transverse electric (TE) and transverse magnetic (TM) polarized light but at slightly different frequencies. Three-dimensional calculations are used to optimize the structure for low loss and narrow beam operation in this low-index photonic crystals. Experimental and theoretical results are in good agreement.
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42.70.Qs Photonic bandgap materials
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Effect of the satellite lines and opacity on the extreme ultraviolet emission from high-density Xe plasmas

Akira Sasaki, Katsunobu Nishihara, Masakatsu Murakami, Fumihiro Koike, Takashi Kagawa, Takashi Nishikawa, Kazumi Fujima, Tohru Kawamura, and Hiroyuki Furukawa

Appl. Phys. Lett. 85, 5857 (2004); http://dx.doi.org/10.1063/1.1834994 (3 pages) | Cited 24 times

Online Publication Date: 9 December 2004

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Extreme ultraviolet (EUV) emission from Xe plasma in the λ=13.5 nm band is theoretically investigated for lithographic application. It appears that a large number of satellite lines due to the 4d–4f, 4d–5p, and 4p–4d transitions significantly contribute to the emission over the spectral range from 10 to 17 nm. At electron densities above 1020∕cm3, laser-produced Xe plasmas attain quasilocal thermodynamic equilibrium (LTE) in order to make the emission intensity in the 13.5 nm band comparable to that in the 11 nm band.
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52.25.Kn Thermodynamics of plasmas
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
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Why can CuInSe2 be readily equilibrium-doped n-type but the wider-gap CuGaSe2 cannot?

Yu-Jun Zhao, Clas Persson, Stephan Lany, and Alex Zunger

Appl. Phys. Lett. 85, 5860 (2004); http://dx.doi.org/10.1063/1.1830074 (3 pages) | Cited 20 times

Online Publication Date: 9 December 2004

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The wider-gap members of a semiconductor series such as diamond→Si→Ge or AlN→GaN→InN often cannot be doped n-type at equilibrium. We study theoretically if this is the case in the chalcopyrite family CuGaSe2→CuInSe2, finding that: (i) Bulk CuInSe2 (CIS, Eg=1.04 eV) can be doped at equilibrium n-type either by Cd or Cl, but bulk CuGaSe2 (CGS, Eg=1.68 eV) cannot; (ii) result (i) is primarily because the Cu-vacancy pins the Fermi level in CGS farther below the conduction band minimum than it does in CIS, as explained by the “doping limit rule;” (iii) Cd doping is better than Cl doping, in that CdCu yields in CIS a higher net donor concentration than ClSe; and (iv) in general, the system shows massive compensation of acceptors (CdIII,VCu) and donors (ClSe,CdCu,InCu).
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61.72.up Other materials
61.72.S- Impurities in crystals
61.72.Bb Theories and models of crystal defects
61.72.J- Point defects and defect clusters
73.20.At Surface states, band structure, electron density of states

Grown-in twin boundaries affecting deformation mechanisms in nc-metals

A. G. Frøseth, P. M. Derlet, and H. Van Swygenhoven

Appl. Phys. Lett. 85, 5863 (2004); http://dx.doi.org/10.1063/1.1835531 (3 pages) | Cited 26 times

Online Publication Date: 9 December 2004

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Molecular dynamics simulations have recently shown that the presence of grown-in twin boundaries in nc-Al promotes slip activity in the form of twin boundary migration. In this letter we investigate the effect of grown-in twin boundaries on the plastic deformation mechanism in nc-Ni and Cu, and show that (1) for these particular fcc metals twin boundary migration is not the favored deformation mechanism and (2) that the Schmid factors of the grown-in twin plane play a correspondingly important role. The results are explained in terms of the different ratios of the extrema of the generalized planar fault curves.
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81.05.Bx Metals, semimetals, and alloys
61.72.Mm Grain and twin boundaries
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.46.-w Structure of nanoscale materials

Noncontact surface tension and viscosity measurements of rhenium in the liquid and undercooled states

Takehiko Ishikawa, Paul-François Paradis, and Shinichi Yoda

Appl. Phys. Lett. 85, 5866 (2004); http://dx.doi.org/10.1063/1.1836002 (3 pages) | Cited 10 times

Online Publication Date: 9 December 2004

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Surface tension and viscosity of liquid rhenium, which have hardly been measured due to the extremely high melting temperature of rhenium, were measured using an electrostatic levitation method combined with the oscillation drop technique. Sample position instability problems caused by the photon pressure of the heating lasers and by sample evaporation were solved by modifying the electrodes design. Good sample stability allowed the measurements of the surface tension and the viscosity over wide temperature ranges including the undercooled states. Over the 2800–3600 K interval, the surface tension of rhenium was measured as σ(T)=2.71×103−0.23(T−Tm), where Tm is the melting temperature, 3453 K. At Tm, the datum agrees well with the literature values. Similarly, on the same temperature range, the viscosity was determined as η(T)=0.08 exp[1.33×105∕(RT)] (mPa s).
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68.03.Cd Surface tension and related phenomena
66.20.-d Viscosity of liquids; diffusive momentum transport
68.03.Fg Evaporation and condensation of liquids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys

Defects and strain relaxation in silicon-germanium-on-insulator formed by high-temperature oxidation

S. W. Bedell, K. Fogel, D. K. Sadana, and H. Chen

Appl. Phys. Lett. 85, 5869 (2004); http://dx.doi.org/10.1063/1.1835532 (3 pages) | Cited 13 times

Online Publication Date: 9 December 2004

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SiGe layers were grown on silicon-on-insulator substrates and oxidized at temperatures from 1200 to 1300 °C to form silicon-germanium-on-insualtor (SGOI) layers. Strain relaxation of the SGOI film is shown to be dislocation mediated and the residual strain scaled with the final SGOI thickness in a manner consistent with equilibrium theory. Stacking faults (SF) are observed in the relaxed SGOI layer and their density increases exponentially with decreasing film thickness. In films below ∼500 math, the SF density becomes comparable with the dislocation density which may be responsible for differences between equilibrium and measured residual strain in thin SGOI layers.
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81.05.Hd Other semiconductors
61.72.Nn Stacking faults and other planar or extended defects
68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.65.Mq Oxidation
68.55.-a Thin film structure and morphology
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Does In-bonding delay GaN-segregation in GaInAsN? A Raman study

T. Tite, O. Pagès, and E. Tournié

Appl. Phys. Lett. 85, 5872 (2004); http://dx.doi.org/10.1063/1.1829387 (3 pages) | Cited 5 times

Online Publication Date: 9 December 2004

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The longitudinal (LO) and transverse (TO) optical Ga–N phonons of thick as-grown Ga1−yInyAs1−xNx∕GaAs (001) layers with x∼3%–4%, i.e., just above the N-solubility limit xs∼2% in GaAs, and y up to 30% are studied by Raman scattering. We observe a three-mode behavior which we associate with Ga–N modes from the isolated Ga4N complexes (∼460 cm−1), the Ga3InN ones (∼480 cm−1) and the GaN-segregated region (∼425 cm−1). The corresponding N fractions are derived via combined contour modeling of the three-mode TO and LO Ga–N Raman lineshapes. We find that substantial In-bonding minimizes GaN segregation only in a very narrow x range of ∼1% just above xs.
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78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Nanoparticle iron-phosphate anode material for Li-ion battery

Dongyeon Son, Eunjin Kim, Tae-Gon Kim, Min Gyu Kim, Jaephil Cho, and Byungwoo Park

Appl. Phys. Lett. 85, 5875 (2004); http://dx.doi.org/10.1063/1.1835995 (3 pages) | Cited 34 times

Online Publication Date: 9 December 2004

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Nanoparticle crystalline iron phosphates (FePO4⋅2H2O and FePO4) were synthesized using a (CTAB) surfactant as an anode material for Li rechargeable batteries. The electrochemical properties of the nanoparticle iron phosphates were characterized with a voltage window of 2.4–0 V. A variscite orthorhombic FePO4⋅2H2O showed a large initial charge capacity of 609 mAh∕g. On the other hand, a tridymite triclinic FePO4 exhibited excellent cyclability: the capacity retention up to 30 cycles was ∼80%, from 485 to 375 mAh∕g. The iron phosphate anodes exhibited the highest reported capacity, while the cathode LiFePO4 has an ideal capacity of 170 mAh∕g.
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82.47.Aa Lithium-ion batteries
82.45.Fk Electrodes
82.45.Yz Nanostructured materials in electrochemistry
61.46.-w Structure of nanoscale materials

Ga+ implantation in the organic crystal (TMTSF)2PF6 by focused ion beam

K. Wang, O. Schneegans, A. Moradpour, and F. Jomard

Appl. Phys. Lett. 85, 5878 (2004); http://dx.doi.org/10.1063/1.1834988 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2004

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Ga ion implantation in the organic crystal (TMTSF)2PF6 (TMTSF: tetramethyl tetraselena fulvalene) is performed using focused ion beam. It is shown that heavy-ion deep implantation inside the sample is obtained for relatively weak ion energy. The electric conduction of the impact areas, at first strongly reduced by ion irradiation, is observed to be reinforced by further ion implantation. The conduction behaviors of the Ga-rich zones can be described by a small polaron hopping model.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.72.up Other materials
61.80.Jh Ion radiation effects
81.65.Cf Surface cleaning, etching, patterning
61.72.S- Impurities in crystals
61.82.Pv Polymers, organic compounds
72.20.Ee Mobility edges; hopping transport

Effects of periodic delta-doping on the properties of GaN:Si films grown on Si (111) substrates

L. S. Wang, K. Y. Zang, S. Tripathy, and S. J. Chua

Appl. Phys. Lett. 85, 5881 (2004); http://dx.doi.org/10.1063/1.1832758 (3 pages) | Cited 22 times

Online Publication Date: 9 December 2004

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In this study, the effects of periodic Si delta-doping on the morphological and optical properties of GaN films grown on Si (111) substrate have been investigated. It is found that the flow rate of Si dopant during growth significantly affects the surface morphology, structural and optical quality of GaN. Compared to undoped GaN on Si(111), films grown using periodic delta-doping show a significant reduction of the in plane tensile stress, which is confirmed by the blueshift of the E2(TO) phonon and band edge photoluminescence peaks. The crack density in GaN films also reduces due to delta-doping.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
68.60.Bs Mechanical and acoustical properties
78.66.Fd III-V semiconductors
68.35.Gy Mechanical properties; surface strains
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.55.Cr III-V semiconductors
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

In situ low-angle x-ray scattering study of phase separation in initially mixed HfO2–SiO2 thin film interfaces

Jeong-Hee Ha, David Chi, and Paul C. McIntyre

Appl. Phys. Lett. 85, 5884 (2004); http://dx.doi.org/10.1063/1.1831554 (3 pages) | Cited 4 times

Online Publication Date: 9 December 2004

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In this letter, we report on phase separation kinetics at initially mixed interfaces of HfO2–SiO2 multilayers measured by low-angle x-ray scattering. Multilayers were fabricated by sputtering and ultraviolet ozone oxidation of ultrathin Hf and Si precursor films. The multilayers were subjected to isothermal anneals in the temperature range 680–762 °C during in situ x-ray scattering measurements. The evolution of the intensity of the multilayer x-ray satellite peaks, the Fourier components of the composition modulation, were consistent with diffusional phase separation of HfO2 and SiO2 during the anneals. The effective interdiffusivity mathL of the HfO2–SiO2 alloy present at the interfaces in the as-deposited multilayers was estimated from the measured intensity change of the first-order satellite reflection as a function of annealing time. The extracted activation energy for the phase separation process was 2.06±0.15 eV for the multilayer samples studied.
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64.75.-g Phase equilibria
78.70.Ck X-ray scattering
68.65.Ac Multilayers
81.15.Cd Deposition by sputtering
81.65.Mq Oxidation
81.40.Gh Other heat and thermomechanical treatments
66.30.Ny Chemical interdiffusion; diffusion barriers

Impact of polydispersity on light propagation in colloidal photonic crystals

Mathieu Allard and Edward H. Sargent

Appl. Phys. Lett. 85, 5887 (2004); http://dx.doi.org/10.1063/1.1835533 (3 pages) | Cited 13 times

Online Publication Date: 9 December 2004

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The influence of polydispersity, or variations in the size of particles, on the transmittance of slabs of colloidal photonic crystals is analyzed. A model based on simulated annealing simulates the assembly of particles with a given size distribution into a dense array. The model reveals the existence of a transition between ordered and random packing at a polydispersity between 3% and 4%; this transition is associated with large changes in optical properties, in the form of greatly increased scattering and reduced contrast associated with the transmittance in and out of the stop band. The predictions of the model correspond closely to experimental measurements.
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42.70.Qs Photonic bandgap materials
82.70.Dd Colloids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Structure and intermixing of GaSb∕GaAs quantum dots

R. Timm, H. Eisele, A. Lenz, S. K. Becker, J. Grabowski, T.-Y. Kim, L. Müller-Kirsch, K. Pötschke, U. W. Pohl, D. Bimberg, and M. Dähne

Appl. Phys. Lett. 85, 5890 (2004); http://dx.doi.org/10.1063/1.1833560 (3 pages) | Cited 20 times

Online Publication Date: 9 December 2004

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We present cross-sectional scanning tunneling microscopy results of GaSb quantum dots in GaAs, grown by metalorganic chemical vapor deposition. The size of the optically active quantum dots with base lengths of 4–8 nm and heights of about 2 nm is considerably smaller than previously published data obtained by other characterization methods. The local stoichiometry, obtained from atomically resolved images, shows a strong intermixing in the partly discontinuous wetting layer with an average GaSb content below 50%, while the GaSb content of the partly intermixed quantum dots is between 60% and 100%.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
66.30.Ny Chemical interdiffusion; diffusion barriers
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
61.66.Bi Elemental solids
61.66.Dk Alloys
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