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1 Apr 2002

Volume 80, Issue 13, pp. 2239-2421

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Direct measurement of the guided modes in LiNbO3 waveguides

A. L. Campillo, J. W. P. Hsu, C. A. White, and C. D. W. Jones

Appl. Phys. Lett. 80, 2239 (2002); http://dx.doi.org/10.1063/1.1464228 (3 pages) | Cited 10 times

Online Publication Date: 26 March 2002

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Mode profiles of the light coming out of Ti diffused waveguides formed in LiNbO3 crystals were imaged using a near-field scanning optical microscope (NSOM). We find that the transverse magnetic mode has a smaller spatial dimension and is closer to the surface of the waveguide than the transverse electric mode. We also measured the phase and intensity distributions of the guided optical modes directly by incorporating the NSOM into an interferometer. The effective index (neff) is determined from the spacings of phase fronts, which equals λ/neff. The experimental results of mode profiles and neff are in good agreement with theoretical simulations. However, an unexpected nonuniform intensity distribution was observed, which could be linked to defects in the waveguide. © 2002 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
07.79.Fc Near-field scanning optical microscopes
42.82.Bq Design and performance testing of integrated-optical systems
07.60.Ly Interferometers

Reduction of reflection losses in ZnGeP2 using motheye antireflection surface relief structures

C. Aydin, A. Zaslavsky, G. J. Sonek, and J. Goldstein

Appl. Phys. Lett. 80, 2242 (2002); http://dx.doi.org/10.1063/1.1466519 (3 pages) | Cited 26 times

Online Publication Date: 26 March 2002

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We report the reduction of surface reflection losses in zinc germanium phosphide (ZnGeP2, or ZGP) crystals by fabricating an antireflection (AR) structure in the substrate itself using subwavelength motheye surface patterns. The motheye AR patterning works by creating a region of gradually varying effective refractive index between air and the ternary nonlinear crystal. Motheye structures were created using interference lithography and reactive-ion etching in a SiCl4 plasma. The ZGP crystal with motheye patterning on the output surface reached a transmittance of ∼67% at a cutoff wavelength of 3.8 μm (close to the theoretical maximum of 73%), with negligible surface contamination from the motheye etching process. The motheye patterning technique could be applied to other nonlinear crystals where surface reflection losses are a concern. © 2002 American Institute of Physics.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.86.+b Optical workshop techniques
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Measurement of laser-induced refractive index changes of Mg-doped congruent and stoichiometric LiNbO3

László Pálfalvi, Gábor Almási, János Hebling, Ágnes Péter, and Katalin Polgár

Appl. Phys. Lett. 80, 2245 (2002); http://dx.doi.org/10.1063/1.1465111 (3 pages) | Cited 12 times

Online Publication Date: 26 March 2002

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Light-induced refractive index changes and nonlinear absorption of undoped and Mg-doped LiNbO3 with congruent and stoichiometric composition were investigated by the Z-scan method using an all-visible argon-ion laser with intensities up to the MW/cm2 level. Charge coupled device recordings demonstrate that the Z-scan method is suitable for quantitative study of Mg-doped samples, while it can be used only for qualitative measurements of undoped samples because of beam fanning in the latter case. Stoichiometric LiNbO3 doped with 5 mol % Mg shows positive refractive index changes opposite to those in cases of undoped congruent, undoped stoichiometric and 5 mol % Mg-doped congruent LiNbO3. The refractive index change of Δne = 2.5×10−5 measured at 0.37 MW/cm2 light intensity for stoichiometric LiNbO3:Mg is six times smaller than that of congruent LiNbO3:Mg at 0.1 MW/cm2. © 2002 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Frequency response of current-driven polarization modulation in vertical-cavity surface-emitting lasers

Guy Verschaffelt, Jan Albert, Irina Veretennicoff, Jan Danckaert, Sylvain Barbay, Giovanni Giacomelli, and Francesco Marin

Appl. Phys. Lett. 80, 2248 (2002); http://dx.doi.org/10.1063/1.1465113 (3 pages) | Cited 14 times

Online Publication Date: 26 March 2002

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We present an experimental study of the current-driven polarization modulation properties of vertical-cavity surface-emitting Lasers (VCSELs). Some VCSELs exhibit a high-contrast polarization flip for a particular value of pump current. By modulating the current around this value we measure the critical modulation amplitude necessary to force current-driven polarization switching as a function of the modulation frequency. We thus obtain the polarization modulation frequency response, which shows the same cut-off frequency as the thermal frequency response. This indicates the necessity to incorporate a temperature-dependent variable in realistic models that describe the polarization behavior of these VCSELs. © 2002 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Multicolor infrared detection realized with two distinct superlattices separated by a blocking barrier

C. C. Chen, H. C. Chen, C. H. Kuan, S. D. Lin, and C. P. Lee

Appl. Phys. Lett. 80, 2251 (2002); http://dx.doi.org/10.1063/1.1466537 (3 pages) | Cited 12 times

Online Publication Date: 26 March 2002

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A multicolor infrared photodetector was realized with two superlattices separated by a blocking barrier. The photoresponse is switchable between 7.5–12 and 6–8.5 μm by the bias polarity, and is also tunable by the bias magnitude in each wavelength regime. In addition, our detector exhibits advantages including little temperature dependence of the spectral response and the same order of responsivity in the two wavelength regimes. The measured peak responsivities in the two regimes are 117 mA/W at 9.8 μm under 1 V and 129 mA/V at 7.4 μm under −0.8 V, respectively. Also, the detectivities are comparable with the conventional multistack detector. The zero background peak detectivities are 2.3×1010 cm Hz0.5/W at 50 K and 9.8 μm under 0.7 V, and 8.7×1010 cm Hz0.5/W at 70 K and 7.4 μm under −0.7 V. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Improvement of on/off ratio in single-shot multichannel demultiplexing by using an optical Kerr gate of a squarylium dye J aggregate film

Yasuhiro Sato, Makoto Furuki, Minquan Tian, Izumi Iwasa, Lyong Sun Pu, and Satoshi Tatsuura

Appl. Phys. Lett. 80, 2254 (2002); http://dx.doi.org/10.1063/1.1463699 (3 pages) | Cited 10 times

Online Publication Date: 26 March 2002

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We demonstrated ultrafast single-shot multichannel demultiplexing by using a squarylium dye J aggregate film as an optical Kerr medium. High efficiency and fast recovery of the optical Kerr responses were achieved when a signal-pulse wavelength was close to the absorption peak of the J aggregate film with off-resonant excitation. The on/off ratio in demultiplexing of 1 Tb/s signals was improved to be approximately 5. By introducing time delay to both horizontal and vertical directions, we succeeded in directly observing the conversion of 1 Tb/s serial signals into two-dimensionally arranged parallel signals. © 2002 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Metallized pyramidal silicon probe with extremely high throughput and resolution capability for optical near-field technology

T. Yatsui, K. Itsumi, M. Kourogi, and M. Ohtsu

Appl. Phys. Lett. 80, 2257 (2002); http://dx.doi.org/10.1063/1.1465520 (3 pages) | Cited 19 times

Online Publication Date: 26 March 2002

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An optical near-field probe with extremely high throughput and resolution capability was fabricated with a metallized pyramidal silicon structure. Using a finite-difference time-domain method, we found the tip parameters that are required for localized surface plasmon resonance at the probe tip. The optical near-field energy distribution on the metallized pyramidal silicon probe was observed by scanning a fiber probe that had an aperture diameter of 50 nm. The spatial distribution profile observed was in good agreement with the numerical results. The throughput and spot size were determined to be 2.3% and 85 nm, respectively. © 2002 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Midinfrared intersubband electroluminescence of Si/SiGe quantum cascade structures

I. Bormann, K. Brunner, S. Hackenbuchner, G. Zandler, G. Abstreiter, S. Schmult, and W. Wegscheider

Appl. Phys. Lett. 80, 2260 (2002); http://dx.doi.org/10.1063/1.1465131 (3 pages) | Cited 31 times

Online Publication Date: 26 March 2002

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Unipolar intersubband lasers like quantum cascade laser structures might be realized not only in III–V semiconductors but also in Si/SiGe multiple layer structures since no optical transitions across the indirect band gap are involved. We report on well-defined intersubband electroluminescence emission of Si/SiGe quantum cascade structures with different active quantum wells parameters. The complex valence band structure and a nonradiative relaxation rate of about 400 fs were calculated by multiband k⋅p formalism including Si/Ge segregation effects. The observed spectral shift of the electroluminescence peak from 146 to 159 meV is described well by quantum confinement of the two lowest heavy hole subbands. The electroluminescence observed reveals transverse magnetic polarization, a spectral line shape that changes with the direction of the current, and low-energy line broadening with an increase in temperature and current. All these features are described well by the k⋅p model calculation. © 2002 American Institute of Physics.
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78.67.De Quantum wells
42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.60.Fi Electroluminescence
73.21.Fg Quantum wells

Three-dimensional optical memory with rewriteable and ultrahigh density using the valence-state change of samarium ions

K. Miura, Jianrong Qiu, S. Fujiwara, S. Sakaguchi, and K. Hirao

Appl. Phys. Lett. 80, 2263 (2002); http://dx.doi.org/10.1063/1.1459769 (3 pages) | Cited 56 times

Online Publication Date: 26 March 2002

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We report the recording, readout, and erasure of a three-dimensional optical memory using the valence-state change of samarium ions to represent a bit. A photoreduction bit of 200 nm diam can be recorded with a femtosecond laser and readout clearly by detecting the fluorescence as a signal (excitation at 488 nm, 0.5 mW Ar+ laser). A photoreduction bit that is stable at room temperature can be erased by photo-oxidation with a cw laser (514.5 nm, 10 mW Ar+ laser). Since photoreduction bits can be spaced 150 nm apart in a layer within glass, a multilayer structure with several hundred layers could be used to record data. A memory capacity of as high as 1 Tbit could thus be achieved in a glass piece with dimensions of 10 mm×10 mm×1 mm. © 2002 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
82.50.-m Photochemistry
42.70.Ce Glasses, quartz
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Structural study of refractory-metal-free C40 TiSi2 and its transformation to C54 TiSi2

T. Yu, S. C. Tan, Z. X. Shen, L. W. Chen, J. Y. Lin, and A. K. See

Appl. Phys. Lett. 80, 2266 (2002); http://dx.doi.org/10.1063/1.1466521 (3 pages) | Cited 6 times

Online Publication Date: 26 March 2002

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The structure of laser-induced refractory-metal-free C40 TiSi2 has been studied by glancing-angle x-ray diffraction (GAXRD) in detail. The result shows that laser-induced C40 TiSi2 has a hexagonal structure with the P6222 space group and lattice parameters a=0.467 nm and c=0.662 nm. The ordering effect and the stress effect on the TiSi2 film are also discussed based on the GAXRD and micro-Raman results. The C40 phase completely transforms to the technologically important C54 phase at a relatively low temperature of 700 °C. © 2002 American Institute of Physics.
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64.70.K- Solid-solid transitions
68.55.-a Thin film structure and morphology
61.66.Fn Inorganic compounds
78.30.-j Infrared and Raman spectra

Structure and defects of vapor-phase-grown diamond nanocrystals

X. Jiang and C. L. Jia

Appl. Phys. Lett. 80, 2269 (2002); http://dx.doi.org/10.1063/1.1458071 (3 pages) | Cited 28 times

Online Publication Date: 26 March 2002

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Diamond nanocrystalline films are prepared by the ion bombardment-assisted gas vapor synthesis technique. The phase quality, morphology and microstructure of the films are investigated by means of Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The grain size in the film ranges from several nanometers to several tens of nanometers. There is a high density of lattice defects, mainly stacking faults and twin boundaries in the nanocrystals. Lattice distortions, vacancies, and dislocations are observed. The growth of nanocrystals and the mechanism of defect formation are discussed in light of the ion impact effect. © 2002 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.U- Carbon/carbon-based materials
61.82.Fk Semiconductors
81.07.Bc Nanocrystalline materials
68.55.-a Thin film structure and morphology
61.80.Jh Ion radiation effects
61.72.Nn Stacking faults and other planar or extended defects
61.72.J- Point defects and defect clusters
68.37.Lp Transmission electron microscopy (TEM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.72.Mm Grain and twin boundaries

Effect of low-temperature preannealing on laser-annealed p+/n ultrashallow junctions

Sungkweon Baek, Taesung Jang, and Hyunsang Hwang

Appl. Phys. Lett. 80, 2272 (2002); http://dx.doi.org/10.1063/1.1463702 (3 pages) | Cited 4 times

Online Publication Date: 26 March 2002

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The effect of low-temperature preannealing on ultrashallow p+/n junctions was examined. An ultrashallow junction was formed by means of B2H6 plasma doping at an energy of 500 V. The junction was activated by low-temperature (300–500 °C) annealing, followed by laser annealing. Compared with control samples which were not preannealed, low-temperature preannealing significantly improves junction characteristics, resulting in a reduction in junction depth and a lower leakage current density. A cross-sectional transmission-electron-microscopy analysis confirmed the lower defect density, which explains the lower leakage current. By optimizing the process conditions, excellent electrical characteristics of the p+/n junction, i.e., a junction depth of 28 nm and a sheet resistance of 250 Ω/sq, can be obtained. © 2002 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
68.37.Lp Transmission electron microscopy (TEM)

Raman mapping, photoluminescence investigations, and finite element analysis of epitaxial lateral overgrown GaN on silicon substrates

M. Benyoucef, M. Kuball, B. Beaumont, and P. Gibart

Appl. Phys. Lett. 80, 2275 (2002); http://dx.doi.org/10.1063/1.1464664 (3 pages) | Cited 13 times

Online Publication Date: 26 March 2002

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Epitaxial lateral overgrown (ELO) GaN grown by metalorganic vapor phase epitaxy on Si substrates was characterized using Raman mapping, photoluminescence (PL) experiments and finite element (FE) analysis. Stress in the structures was determined from the E2 phonon frequency and compared to FE results. Low temperature PL spectra are dominated by donor bound exciton (DBE) emission at (3.457–3.459) eV. PL spectra reveal a peak at ∼3.404 eV in window regions attributed to structural defects in the GaN. Differences in crystalline quality between window and overgrown regions of ELO GaN were investigated. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
68.60.Bs Mechanical and acoustical properties
02.70.Dh Finite-element and Galerkin methods
63.20.-e Phonons in crystal lattices

Determining the relationship between local lattice strain and slip systems of dislocations around shallow trench isolation by convergent-beam electron diffraction

Akio Toda, Nobuyuki Ikarashi, Haruhiko Ono, and Kensuke Okonogi

Appl. Phys. Lett. 80, 2278 (2002); http://dx.doi.org/10.1063/1.1465517 (3 pages) | Cited 9 times

Online Publication Date: 26 March 2002

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We clarified the generation of process-induced dislocations around a shallow trench isolation (STI) by using convergent-beam electron diffraction. Comparing the resolved shear strain (RSS) of 12 slip systems, we found that at the trench bottom corner the RSS on slip systems (1 −1 1)[0 1 1] and (1 −1 1)[1 0 −1] was largest in all slip systems. In fact, the dislocations of slip systems (1 −1 1)[0 1 1] and (1 −1 1)[1 0 −1] were observed around the trench bottom corner more often than those of any other slip systems. We also found that the large RSS at the trench bottom corner may be due to the corner shape or the intrinsic stress induced during oxidation. Therefore, to control dislocation around STI, the oxidation-induced stress at the trench bottom corner must be reduced, and the shape of the bottom corner must be controlled. © 2002 American Institute of Physics.
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81.65.Mq Oxidation
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Lk Linear defects: dislocations, disclinations
68.60.Bs Mechanical and acoustical properties

Delayed nucleation during molecular-beam epitaxial growth of GaN observed by line-of-sight quadrupole mass spectrometry

G. Koblmüller, P. Pongratz, R. Averbeck, and H. Riechert

Appl. Phys. Lett. 80, 2281 (2002); http://dx.doi.org/10.1063/1.1465530 (3 pages) | Cited 11 times

Online Publication Date: 26 March 2002

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We present a nucleation study for molecular-beam epitaxial growth of GaN on 6H-SiC and sapphire using Rutherford backscattering, atomic force microscopy, and in situ line-of-sight quadrupole mass spectrometry. Film thickness measurements by Rutherford backscattering reveal a strong deviation from thickness calculations assuming steady-state growth. We differentiate two regimes of growth, initially a highly nonlinear growth mode during island formation and later a linear growth mode after coalescence of islands. The mechanisms leading to the nonlinear behavior are attributed to energy barriers that supress immediate nucleation and provide for a substantial desorption of Ga and N atoms. Employing line-of-sight quadrupole mass spectrometry, we developed a quantitative in situ method to determine the amount of desorbing Ga atoms during the entire GaN growth procedure. The amount of initial GaN desorption in heteroepitaxy is independent of the substrate material and is as high as 8±1.5 nm. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.43.Mn Adsorption kinetics
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.37.Ps Atomic force microscopy (AFM)
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Differentiating between elastically bent rectangular beams and plates

S. K. Kaldor and I. C. Noyan

Appl. Phys. Lett. 80, 2284 (2002); http://dx.doi.org/10.1063/1.1459762 (3 pages) | Cited 9 times

Online Publication Date: 26 March 2002

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We report x-ray microdiffraction curvature measurements of a (100)-type Si single crystal loaded in four-point bending and provide experimental verification of a procedure for differentiating between anisotropic, elastically bent beams and plates. In general usage, beam and plate components are distinguished by dimensions alone. In mechanics, however, beams and plates are differentiated based on their flexural rigidity and stress state. Since current textbooks do not provide a quantitative technique for selecting the proper constitutive equations for these two types of structures, we suggest the extension of an analysis for isotropic materials originated by Searle [G. F. C. Searle, Experimental Elasticity (Cambridge University Press, Cambridge, 1908), pp. 40–58] and expanded on by Ashwell [D. G. Ashwell, J. R. Aeronaut. Soc. 54, 708 (1950)]. We demonstrate that, by varying the degree of bending of an anisotropic strip, a single specimen can behave as both a beam and a plate, as is predicted by this analysis.© 2002 American Institute of Physics.
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46.70.De Beams, plates, and shells
62.20.D- Elasticity
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep

Effective method for stress reduction in thick porous silicon films

Han-Su Kim, Eric C. Zouzounis, and Ya-Hong Xie

Appl. Phys. Lett. 80, 2287 (2002); http://dx.doi.org/10.1063/1.1465130 (3 pages) | Cited 9 times

Online Publication Date: 26 March 2002

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A promising stress control process is demonstrated to achieve near-zero stress levels in thick porous silicon (PS) films. Stress reduction is necessary for thick PS structures to be used for radio-frequency applications such as on-chip inductors and transmission lines that require very thick (>100 μm) insulating materials. This study employs a standard sample structure with 50-μm-thick PS films formed on p+ substrates through anodization under 50 mA/cm2 and 25% HF concentration. Mass spectroscopy analysis shows that the desorption of hydrogen is correlated with the stress evolution in PS films. As-prepared PS films are under compressive stress. Thermal annealing in N2 ambient turns it into tensile stress. Further annealing in an oxidizing ambient restores the compressive stress. Such stress evolution can be explained by the atomic structure changes on the pore walls of PS films: H2-passivated and oxidized Si surfaces result in compression in PS films, whereas reconstructed state results in tension. These findings are used to fabricate thick PS films with negligible stress (<1 MPa) at room temperature. © 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Mq Oxidation
68.43.Mn Adsorption kinetics
82.45.Mp Thin layers, films, monolayers, membranes
81.65.Rv Passivation

Development of 〈110〉 texture in copper thin films

H. L. Wei, Hanchen Huang, C. H. Woo, R. K. Zheng, G. H. Wen, and X. X. Zhang

Appl. Phys. Lett. 80, 2290 (2002); http://dx.doi.org/10.1063/1.1466518 (3 pages) | Cited 18 times

Online Publication Date: 26 March 2002

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Apart from the scientific interest, texture development in copper thin films is of crucial importance to their applications as interconnects or corrosion resistant coating. We report here a dominant 〈110〉 texture of copper thin films—preferred for oxidation-resistant applications—deposited by direct current magnetron sputtering. Scanning electron microscopy shows that the copper films go through a transition from 〈111〉 columns to 〈110〉 hillocks as the deposition proceeds. Cross-sectional transmission electron microscopy (TEM) indicates that the 〈110〉 grains nucleate at boundaries of 〈111〉 grains. Further, we have proposed a stress-driven nucleation and growth model of 〈110〉 grains based on the x-ray diffraction characterization and the TEM observations. © 2002 American Institute of Physics.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
85.40.Ls Metallization, contacts, interconnects; device isolation
81.05.Bx Metals, semimetals, and alloys
81.15.Cd Deposition by sputtering
61.72.Mm Grain and twin boundaries

Influence of different types of threading dislocations on the carrier mobility and photoluminescence in epitaxial GaN

J. Y. Shi, L. P. Yu, Y. Z. Wang, G. Y. Zhang, and H. Zhang

Appl. Phys. Lett. 80, 2293 (2002); http://dx.doi.org/10.1063/1.1465531 (3 pages) | Cited 30 times

Online Publication Date: 26 March 2002

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High-resolution x-ray diffraction has been used to analyze the type and density of threading dislocations in a series (0001)-oriented GaN epitaxial film. Photoluminescence (PL) and carrier mobility of the films are measured at room temperature. The intensities of both the band edge (3.42 eV) peak and yellow luminescence (YL) are strongly related to the threading dislocation density of the GaN films. But different types of dislocations show different relationship with the intensities of PL and YL. The fundamental correlation is found not only between the interaction of edge- and screw-type dislocations and the carrier mobility but also between the interaction and the intensities of both the band edge peak and the YL. © 2002 American Institute of Physics.
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73.61.Ey III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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
61.72.Lk Linear defects: dislocations, disclinations
73.50.Dn Low-field transport and mobility; piezoresistance

Formation of Cu diffusion channels in Ta layer of a Cu/Ta/SiO2/Si structure

S. Li, Z. L. Dong, K. Maung Latt, H. S. Park, and T. White

Appl. Phys. Lett. 80, 2296 (2002); http://dx.doi.org/10.1063/1.1465107 (3 pages) | Cited 11 times

Online Publication Date: 26 March 2002

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Three mechanisms for the formation of Cu diffusion channels in the Ta layer of a Cu/Ta/SiO2/Si structure are proposed. First, it is suggested that stacking faults formed during the recovery process induce localized regions of high internal energy in the Ta layer, from which Cu channels originate. Second, chemical reaction occurs at 800 °C and forms Ta4CuO11 across the Cu/Ta interface in Cu and Ta layers, which opens up channels for Cu diffusion. Third, triple junctions at the grain boundary of the Cu and Cu/Ta interface provide sites for the initiation of channel formation at 800 °C. At 950 °C, these channels in the diffusion barrier are absent, but Ta was oxidized into disordered Ta2O5 that may contain pathways for Cu diffusion. © 2002 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.Nn Stacking faults and other planar or extended defects
61.72.Mm Grain and twin boundaries
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
61.72.Cc Kinetics of defect formation and annealing

High pressure effects on the luminescent properties and structure of coumarin 153

Hong Li, Bo Zhong, Liming He, Guoqiang Yang, Yi Li, Shikang Wu, and Jing Liu

Appl. Phys. Lett. 80, 2299 (2002); http://dx.doi.org/10.1063/1.1465524 (3 pages) | Cited 4 times

Online Publication Date: 26 March 2002

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The absorption and emission spectra of coumarin 153 (C153) at high pressure have been detected up to 7.0 GPa. Because of the strong electron-withdrawing group at 7 site in the coumarin, the fluorescence spectrum of the title compound exhibits one band emission at ambient pressure from its charge transfer (CT) state. At higher pressure, the decreased distance of the crystal face, as proved by in situ x-ray diffraction measurement, and the increased interactions between the molecules enhance the energy gap between the local excited (LE) state and the CT state. Two-band emissions of C153, from LE and CT, respectively, have been observed. © 2002 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
78.55.Kz Solid organic materials
61.66.Hq Organic compounds
42.70.Hj Laser materials
71.70.-d Level splitting and interactions
71.20.Rv Polymers and organic compounds
42.70.Jk Polymers and organics
78.40.Me Organic compounds and polymers

Deformation potentials of the E1(TO) mode in AlN

V. Darakchieva, P. P. Paskov, T. Paskova, J. Birch, S. Tungasmita, and B. Monemar

Appl. Phys. Lett. 80, 2302 (2002); http://dx.doi.org/10.1063/1.1465105 (3 pages) | Cited 17 times

Online Publication Date: 26 March 2002

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The deformation potentials of the E1(TO) mode in AlN are experimentally determined by combining infrared reflection spectroscopy and x-ray diffraction measurements and using a reported value of the Raman-stress factor for hydrostatically stressed bulk AlN. The deformation potentials are found to strongly depend on published stiffness constants of AlN. A comparison with earlier theoretically calculated values of the deformation potentials is made.© 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
78.66.Fd III-V semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
68.55.-a Thin film structure and morphology
78.30.Fs III-V and II-VI semiconductors
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Tunable reflectance Mg–Ni–H films

J. Isidorsson, I. A. M. E. Giebels, R. Griessen, and M. Di Vece

Appl. Phys. Lett. 80, 2305 (2002); http://dx.doi.org/10.1063/1.1463205 (3 pages) | Cited 26 times

Online Publication Date: 26 March 2002

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Mg2NiHx switchable mirrors, which switch from shiny metallic Mg2Ni to transparent Mg2NiH4, are shown to exhibit also dramatic reversible changes in reflectance at remarkably low hydrogen concentrations. Already for x ≅ 0.3 a 232 nm thick Mg2NiHx film has an absorptance of ∼ 90% over the whole visible optical spectrum. The transition from highly reflective to black occurs in the concentration interval 0.1<x<0.3. The volume changes involved are one order of magnitude smaller than in the transition from reflecting to transparent. This is expected to enhance the lifetime of future devices based on these materials. © 2002 American Institute of Physics.
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78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics
42.79.Bh Lenses, prisms and mirrors
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High-performance polymer light-emitting diodes doped with a red phosphorescent iridium complex

Fang-Chung Chen, Yang Yang, Mark E. Thompson, and Junji Kido

Appl. Phys. Lett. 80, 2308 (2002); http://dx.doi.org/10.1063/1.1462862 (3 pages) | Cited 119 times

Online Publication Date: 26 March 2002

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High efficiency has been achieved in polymer light-emitting diodes (PLEDs) exhibiting red emission by doping a fluorescence host material, poly(vinylcarbazole) (PVK), with an iridium(III) complex, bis[2-(2′-benzothienyl)-pyridinato-N,C3′]iridium(acetylacetonate) (BtpIr). The electroluminescence spectrum has a maximum wavelength of 614 nm. The highest external quantum efficiency is 3.3%. Due to its short triplet excited lifetime (∼5 μs), the quenching of the triplet exciton in BtpIr-doped PVK PLEDs has been shown to be suppressed compared to platinum(II)-2,8,12,17-tetraethyl- 3,7,13,18-tetramethylporphyrin-doped PVK PLEDs. 65% of the peak efficiency can be sustained at high-current density and at the very high brightness of 1350 cd/m2. We suggest that both triplet–triplet annihilation and polaron–triplet annihilation involves exciton quenching. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.38.-k Polarons and electron-phonon interactions
85.60.Pg Display systems

Improved chemical stability of Ti-doped MgB2 in water

Y. Zhao, C. H. Cheng, T. Machi, N. Koshizuka, and M. Murakami

Appl. Phys. Lett. 80, 2311 (2002); http://dx.doi.org/10.1063/1.1465521 (3 pages) | Cited 3 times

Online Publication Date: 26 March 2002

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We investigated the degradation of critical current density (Jc) and irreversibility field (Hirr) of pure and Ti-doped MgB2 bulks by exposing the samples to water for a total of 10, 48, 100, and 124 h. We found that both Jc and Hirr of the samples were degraded by exposure to water, in various degrees depending on the doping level. In the same exposure duration, the Ti-doped samples exhibited a less sensitivity to water, which was confirmed by the less degradation of Jc and Hirr. Our results demonstrate that Ti doping is not only effective in improving the superconducting properties of MgB2 but also in enhancing its chemical stability against water. © 2002 American Institute of Physics.
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74.25.Sv Critical currents
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
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