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22 Apr 2002

Volume 80, Issue 16, pp. 2821-3018

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Optical switching in midinfrared light-emitting diodes

A. Krier, V. V. Sherstnev, H. H. Gao, A. M. Monahov, and G. Hill

Appl. Phys. Lett. 80, 2821 (2002); http://dx.doi.org/10.1063/1.1470690 (3 pages) | Cited 3 times

Online Publication Date: 16 April 2002

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We report on the optical quenching of electroluminescence in midinfrared light-emitting diodes operating at 3.0 μm. The source is based on a symmetrical double heterostructure with large band offsets and is effectively switched off using coherent visible light. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
61.82.Fk Semiconductors
78.60.Fi Electroluminescence

Role of defect centers in recombination processes in GaN monocrystals

N. V. Joshi, A. Cros, A. Cantarero, H. Medina, O. Ambacher, and M. Stutzmann

Appl. Phys. Lett. 80, 2824 (2002); http://dx.doi.org/10.1063/1.1471938 (3 pages) | Cited 1 time

Online Publication Date: 16 April 2002

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A confocal fluorescence microscopic study was carried out on GaN monocrystals grown by molecular beam epitaxy and doped with Mn. The samples were irradiated with mid band gap radiation (488 nm) rather than ultraviolet, and it was found that a strong yellow radiation was emitted by defect centers. Three-dimensional images clearly reveal not only the size and the form of the illuminating defect centers but also their orientations with respect to the plane on which these defects were grown. This is a direct evidence for the radiative recombination at the defect centers when excited by the midgap radiation. © 2002 American Institute of Physics.
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78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Technique to enhance the throughput on a near-field aperture by the use of self-focusing effect

Ki-Bong Song, Jeongyong Kim, and Kang-Ho Park

Appl. Phys. Lett. 80, 2827 (2002); http://dx.doi.org/10.1063/1.1473231 (3 pages) | Cited 2 times

Online Publication Date: 16 April 2002

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A technique to increase the throughput of a near-field aperture on a cantilever aperture is described. Using the self-focusing effect due to nonlinear optical Kerr effect in as-evaporated As2S3 glass, we found that the throughput of the near-field aperture with an aperture diameter ∼ 100 nm increases over 100 times compared with conventional tapered fiber tips. A theoretical qualitative analysis using the modified nonparaxial model to estimate the enhancement of the throughput is in good agreement with observed experimental results. © 2002 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Intraband relaxation time in wurtzite InGaN/GaN quantum-well structures with (10math0) crystal orientation

Seoung-Hwan Park

Appl. Phys. Lett. 80, 2830 (2002); http://dx.doi.org/10.1063/1.1471568 (3 pages) | Cited 2 times

Online Publication Date: 16 April 2002

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Intraband relaxation time is investigated theoretically for a wurtzite InGaN/GaN quantum well (QW) with a (10math0) crystal orientation. The results are compared with those of (0001)-oriented QW structures. It is found that the linewidths for the h–h scattering of the (10math0)-oriented QW is largely reduced compared to that of the (0001)-oriented QW. This is because the hole effective mass of the (10math0)-oriented QW is reduced due to the inclusion of the anisotropic strain in the QW plane. In the case of the (0001)-oriented QW, considering only the h–h scattering near subband edges is a good approximation. On the other hand, in the case of the (10math0)-oriented QW, linewidths for the e–e and e–h scatterings are comparable to that for the h–h scattering. The intraband relaxation times near band edges for (0001)- and (10math0)-oriented QWs are about 20 and 25 fs at a sheet carrier density of 2×1012 cm−2, respectively. These values are shorter than those (40–100 fs) reported for InP and GaAs. © 2002 American Institute of Physics.
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73.21.Fg Quantum wells
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.65.Fg Quantum wells
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
78.67.De Quantum wells

Optical gain and loss in 3 μm diode “W” quantum-well lasers

Sergey Suchalkin, David Westerfeld, Dmitrii Donetski, S. Luryi, G. Belenky, Ramon Martinelli, Igor Vurgaftman, and Jerry Meyer

Appl. Phys. Lett. 80, 2833 (2002); http://dx.doi.org/10.1063/1.1471571 (3 pages) | Cited 16 times

Online Publication Date: 16 April 2002

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Gain in broad-area midinfrared diode “W” lasers (λ = 3–3.1 μm) has been measured using lateral mode spatial filtering combined with the Hakki–Paoli approach. The internal optical loss of ≈19 cm−1 determined from the gain spectra was the same for devices with either ten or five period active regions and nearly constant in the temperature range between 80 and 160 K. Analysis of the differential gain and spontaneous emission spectra shows that the main contribution to the temperature dependence of the threshold current is Auger recombination, which dominates within almost the entire temperature range studied (80–160 K). © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.50.-p Quantum optics
42.55.Wd Fiber lasers

Subpicosecond transmission change in semiconductor–embedded photonic crystal slab: Toward ultrafast optical switching

Makoto Shimizu and Teruya Ishihara

Appl. Phys. Lett. 80, 2836 (2002); http://dx.doi.org/10.1063/1.1472462 (3 pages) | Cited 33 times

Online Publication Date: 16 April 2002

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We have measured the subpicosecond photoinduced transmission change of the photonic crystal slab, in which inorganic–organic layered perovskite semiconductor is embedded for large optical nonlinearity. It is observed that sharp transmission dips shift to the blue during the irradiation of the pump pulse. This result is explained in terms of the change of the polariton dispersion relation due to the excitonic optical Stark effect. Possible application for ultrafast optical switching is discussed. © 2002 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.70.Jk Polymers and organics
42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.20.Jq Electro-optical effects
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.40.Fy Semiconductors
78.40.Me Organic compounds and polymers

White electroluminescence from hydrogenated amorphous-SiNx thin films

Zingway Pei, Y. R. Chang, and H. L. Hwang

Appl. Phys. Lett. 80, 2839 (2002); http://dx.doi.org/10.1063/1.1473230 (3 pages) | Cited 34 times

Online Publication Date: 16 April 2002

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White electroluminescence (EL) was observed from hydrogenated amorphous-SiNx-based light-emitting device. Silicon nitride thin films were deposited on the indium-tin-oxide (ITO)-coated glass substrate by plasma enhanced chemical vapor deposition method with a mixture of Ar-diluted 5% SiH4 and pure N2 gases, in the ratio 2 to 1. Measured x value of the film is 0.56, and the corresponding photoluminescence of a-SiN0.56:H thin film exhibited a red-infrared spectrum, centered at 630 nm. The layer structure of the EL device is ITO/a-SiN0.56:H (80 nm)/Al, with light emitting from the ITO layer, recognizable by the naked eye in the dark, under the 14 V forward bias conditions. White EL spectra from ∼400 to 750 nm, with a central peak at 560 nm, were observed in the hydrogenated amorphous silicon nitride EL device. A carrier transport mechanism was suggested, and the EL was attributed to the recombination of carriers through the luminescent states. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition

Analytic method for evaluation of the field of a charge traversing a geometric discontinuity

S. Banna and L. Schächter

Appl. Phys. Lett. 80, 2842 (2002); http://dx.doi.org/10.1063/1.1472477 (3 pages) | Cited 1 time

Online Publication Date: 16 April 2002

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An analytic time-domain method is developed for the electromagnetic field generated by a charge traversing a geometric discontinuity. The essence of the method employed here is to use the linear independence of the exponential functions, that control the temporal behavior of the field. As a result, we avoid the large (“infinite”) matrix inversion necessary for a frequency-domain solution. This method was utilized for the investigation of the wake generated by electrons in an optical accelerator as well as evaluation of the emittance growth and energy spread. © 2002 American Institute of Physics.
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41.60.-m Radiation by moving charges

Threshold reduction in quantum cascade lasers with partially undoped, dual-wavelength interdigitated cascades

Axel Straub, Trinesha S. Mosely, Claire Gmachl, Raffaele Colombelli, Mariano Troccoli, Federico Capasso, Deborah L. Sivco, and Alfred Y. Cho

Appl. Phys. Lett. 80, 2845 (2002); http://dx.doi.org/10.1063/1.1472473 (3 pages) | Cited 15 times

Online Publication Date: 16 April 2002

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A dual-wavelength quantum cascade (QC) laser with an interdigitated cascade is presented. Aside from providing two-wavelength operation at 8.0 and 9.5μm wavelength, this laser design was used to test the role of extrinsic carriers in the injectors. An interdigitated cascade was grown with undoped injectors bridging 9.5 and 8.0 μm active regions, but doped injectors bridging 8.0 and 9.5 μm active regions. Clear laser action on both wavelengths demonstrates that doping of all injector regions is not a firm requirement for QC lasers. Comparison with a conventionally doped interdigitated cascade QC laser shows a threshold reduction by a factor of approximately 2 for the laser based on the active regions preceded by the undoped injector. This can be understood from the absence or strong reduction of impurity scattering related to the dopant ions. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.60.Fi Electroluminescence

Measurements of InGaAs metal–semiconductor–metal photodetectors under high-illumination conditions

K. Aliberti, M. Wraback, M. Stead, P. Newman, and H. Shen

Appl. Phys. Lett. 80, 2848 (2002); http://dx.doi.org/10.1063/1.1473235 (3 pages) | Cited 3 times

Online Publication Date: 16 April 2002

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We report on temporal response measurements of InGaAs metal–semiconductor–metal photodetectors (MSM–PDs) under high-illumination conditions. The peak current efficiency of the MSM–PDs decreases as optical pulse energy increases due to space-charge-screening effects. The screening effect begins to occur at an optical pulse energy as low as 1.0 pJ, as predicted by a recent two-dimensional model. The fall time and full width at half maximum of the impulse response increase as the optical pulse energy increases and decrease as the bias voltage increases. For optical pulse energies between 1.0 and 100 pJ, the rise time displays a U-shaped behavior as the bias voltage increases. This may be associated with the shape of the electron velocity-field characteristic in conjunction with the screening of the dark field by optical generated carriers.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Operation and performance of a free electron laser oscillator down to 190 nm

M. Marsi, M. Trovò, R. P. Walker, L. Giannessi, G. Dattoli, A. Gatto, N. Kaiser, S. Günster, D. Ristau, M. E. Couprie, D. Garzella, J. A. Clarke, and M. W. Poole

Appl. Phys. Lett. 80, 2851 (2002); http://dx.doi.org/10.1063/1.1471934 (3 pages) | Cited 1 time

Online Publication Date: 16 April 2002

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We present recent results obtained by the European Free Electron Laser (FEL) project at the ELETTRA storage ring. Coherent and tunable light was produced in the ultraviolet down to below 190 nm, the shortest lasing wavelength obtained so far with a FEL oscillator. The performance of the FEL is described, together with a series of technical solutions that have been adopted on it. These solutions increase its validity as a source for applications, and demonstrate the potential of FEL oscillators to become sources with features in the vacuum ultraviolet. © 2002 American Institute of Physics.
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41.60.Cr Free-electron lasers
29.20.db Storage rings and colliders
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Generation of micrometer-scale discharge in a supercritical fluid environment

Tsuyohito Ito and Kazuo Terashima

Appl. Phys. Lett. 80, 2854 (2002); http://dx.doi.org/10.1063/1.1470695 (3 pages) | Cited 31 times

Online Publication Date: 16 April 2002

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The generation of micrometer-scale discharge in very high-pressure CO2 up to a supercritical fluid (SCF) environment using micrometer-gap (1, 2 μm) electrodes has been performed. A peculiar characteristic of breakdown voltage for CO2 is reported here. The results reveal an inflection near 2.5 MPa and a trough near the critical point. Near the critical point, the discharge can be generated with almost one fifth of the voltage required for a conventional gas, as estimated from Paschen’s law, which is probably caused by unstable clusters in SCF. This result reveals that an ionized state or plasma state in a SCF environment can be generated with very low voltage. © 2002 American Institute of Physics.
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52.80.-s Electric discharges
64.70.F- Liquid-vapor transitions
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
36.40.Gk Plasma and collective effects in clusters
82.30.Nr Association, addition, insertion, cluster formation
82.33.Fg Reactions in clusters
82.40.Fp Shock wave initiated reactions, high-pressure chemistry
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Designing a heterostructure for the quantum receiver

A. A. Kiselev, K. W. Kim, and E. Yablonovitch

Appl. Phys. Lett. 80, 2857 (2002); http://dx.doi.org/10.1063/1.1472480 (3 pages) | Cited 5 times

Online Publication Date: 16 April 2002

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In this letter, we develop optimal parameters for a structure which is suitable for the realization of a coherent quantum receiver. Conditions including predefined photon wavelength, strain, small Zeeman splitting of the electron levels, and large Zeeman effect for quantum-confined light holes are satisfied simultaneously for the structure based on the InGaAsP solid solutions. We are able to achieve designs with wavelengths of 1.3 and 1.55 μm that are desirable for optoelectronic applications. © 2002 American Institute of Physics.
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42.50.-p Quantum optics
73.21.Fg Quantum wells
78.67.De Quantum wells
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
68.65.Fg Quantum wells

Photoreflectance spectra of a ZnO heteroepitaxial film on the nearly lattice-matched ScAlMgO4 (0001) substrate grown by laser molecular-beam epitaxy

S. F. Chichibu, A. Tsukazaki, M. Kawasaki, K. Tamura, Y. Segawa, T. Sota, and H. Koinuma

Appl. Phys. Lett. 80, 2860 (2002); http://dx.doi.org/10.1063/1.1471374 (3 pages) | Cited 32 times

Online Publication Date: 16 April 2002

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Photoreflectance spectra of a high-quality ZnO epilayer on the ScAlMgO4 (0001) substrate grown by laser molecular-beam epitaxy exhibited clear excitonic resonances due to three excitons associated with uppermost valence bands (A, B, and C excitons). The oscillator strengths of the B and C excitons are larger than that of the A exciton. Their broadening was interpreted to be due to the contribution by exciton–polaritons in terms of large longitudinal–transverse splitting of respective excitons. Dependence of the exciton energy on temperature was well fitted assuming the Bose–Einstein statistics giving the Einstein characteristic temperature ΘE of 380 K (33 meV). © 2002 American Institute of Physics.
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78.66.Hf II-VI semiconductors
71.35.Gg Exciton-mediated interactions
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.55.Et II-VI semiconductors

Influence of substrate bias voltage on surface morphology and nanocluster arrangement of gold containing amorphous hydrogenated carbon

Ivan R. Videnović, Verena Thommen, Peter Oelhafen, Daniel Mathys, Marcel Düggelin, and Richard Guggenheim

Appl. Phys. Lett. 80, 2863 (2002); http://dx.doi.org/10.1063/1.1471380 (3 pages) | Cited 2 times

Online Publication Date: 16 April 2002

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Gold containing amorphous hydrogenated carbon (a-C:H/Au) thin films are studied by means of ex situ atomic-force and scanning electron microscopy, and in situ x-ray photoelectron spectroscopy. Introducing a dc substrate bias voltage during magnetron plasma-assisted chemical-vapor deposition of a-C:H/Au results in significant changes of surface morphology and nanocluster arrangement, compared to films deposited on electrically grounded substrates. Grounded samples are rather flat (below 1 nm of roughness), with topmost Au clusters covered with a very thin, nanometer-range layer of a-C:H. On the other hand, the biased sample surface is characterized by large bump structures (up to 13 nm in height) and bald gold clusters. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
79.60.Dp Adsorbed layers and thin films

Microscopic evidence of point defect incorporation in laterally overgrown GaN

S. Gradečak, V. Wagner, M. Ilegems, T. Riemann, J. Christen, and P. Stadelmann

Appl. Phys. Lett. 80, 2866 (2002); http://dx.doi.org/10.1063/1.1470696 (3 pages) | Cited 3 times

Online Publication Date: 16 April 2002

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Electron microscopy techniques are applied to investigate structural and optical properties of GaN layers selectively grown by hydride vapor phase epitaxy on crystalline GaN seed layers deposited on (0001)Al2O3 substrates. Regions with different optical properties are observed in the cross- sections of the layers. They are defined by the crystallographic planes that serve as growth facets. We give a simple geometrical explanation of point defect incorporation occurring more easily for the {11math2} GaN than for the {0001} GaN growth facets. Microscopic evidences supporting the model are higher concentrations of point-like defects and local strain variations in laterally grown regions that are revealed by high-resolution electron microscopy. © 2002 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
61.72.J- Point defects and defect clusters
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Effect of hydrogen doping on ultraviolet emission spectra of various types of ZnO

Naoki Ohashi, Takamasa Ishigaki, Nobuhiro Okada, Takashi Sekiguchi, Isao Sakaguchi, and Hajime Haneda

Appl. Phys. Lett. 80, 2869 (2002); http://dx.doi.org/10.1063/1.1470703 (3 pages) | Cited 85 times

Online Publication Date: 16 April 2002

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A pulse-modulated plasma irradiation technique was applied to hydrogenation of ZnO. Three kinds of ZnO samples were employed to investigate the electronic state of hydrogen in ZnO. Secondary-ion-mass-spectroscopy analysis using isotope tracer revealed that the surface layer to 100 nm was doped with hydrogen after the irradiation and its concentration was in the order of 1016 cm−3. The efficiency of band edge emission was increased by the hydrogenation. However, the the degree of the improvements depended on impurity and defect concentration in the original samples. It was concluded that hydrogen in ZnO passivates deep donor and acceptor states by electron transfer from hydrogen to the defects. © 2002 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.65.Rv Passivation
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.S- Impurities in crystals

Optical and luminescence characteristics of thermally evaporated pentacene films on Si

S. P. Park, S. S. Kim, J. H. Kim, C. N. Whang, and S. Im

Appl. Phys. Lett. 80, 2872 (2002); http://dx.doi.org/10.1063/1.1471929 (3 pages) | Cited 6 times

Online Publication Date: 16 April 2002

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We report on the optical and luminescence properties of pentacene films deposited on n-Si by thermal evaporation at room temperature, 40, 60, 80, and 120 °C. Ellipsometric spectra of the films deposited at room temperature and 60 °C exhibited a main absorption peak at 1.82 eV and additional weak features at higher energy levels. Photoluminescence spectra taken at room temperature revealed band-to-exciton and band-to-acceptor transitions at 1.7 and 1.76 eV, respectively. An electroluminescence band was also observed near 1.65 eV under a forward bias from p-pentacene/n-Si diodes which show strong rectifying behavior. © 2002 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials

Nitrogen-doped GaAsP light-emitting diodes with junctions grown by hydride vapor-phase epitaxy

Tadashige Sato and Megumi Imai

Appl. Phys. Lett. 80, 2875 (2002); http://dx.doi.org/10.1063/1.1473693 (3 pages)

Online Publication Date: 16 April 2002

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Nitrogen-doped GaAsP light-emitting diodes (LEDs) with grown junctions have been fabricated on GaP substrates using hydride vapor-phase epitaxy. A p+/p-layer structure was employed to reduce light absorption and to optimize the carrier concentration at the junction. The carrier concentration in the p layer of the structure plays the important role of improvement of the luminous intensity, and is optimized at 3×1017 cm−3. The LEDs were 20% brighter than those commercially available with diffused junctions. Reliability studies showed good stability through 168 h of operation, enough to suggest they could be used as commercial products. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Creation and suppression of point defects through a kick-out substitution process of Fe in InP

Y. W. Zhao, H. W. Dong, Y. H. Chen, Y. H. Zhang, J. H. Jiao, J. Q. Zhao, L. Y. Lin, and S. Fung

Appl. Phys. Lett. 80, 2878 (2002); http://dx.doi.org/10.1063/1.1473695 (2 pages) | Cited 8 times

Online Publication Date: 16 April 2002

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Indium antisite defect InP-related photoluminescence has been observed in Fe-diffused semi-insulating (SI) InP. Compared to annealed undoped or Fe-predoped SI InP, there are fewer defects in SI InP obtained by long-duration, high-temperature Fe diffusion. The suppression of the formation of point defects in Fe-diffused SI InP can be explained in terms of the complete occupation by Fe at indium vacancy. The InP defect is enhanced by the indium interstitial that is caused by the kick out of In and the substitution at the indium site of Fe in the diffusion process. Through these Fe-diffusion results, the nature of the defects in annealed undoped SI InP is better understood. © 2002 American Institute of Physics.
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61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
78.55.Cr III-V semiconductors
66.30.J- Diffusion of impurities

Highly stressed carbon film coatings on silicon: Potential applications

T. Sharda, T. Soga, T. Jimbo, and M. Umeno

Appl. Phys. Lett. 80, 2880 (2002); http://dx.doi.org/10.1063/1.1471379 (3 pages) | Cited 8 times

Online Publication Date: 16 April 2002

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Highly stressed and strongly adhered nanocrystalline diamond films are grown on Si substrates by providing controlled and continuous bias current density (BCD) in microwave plasma chemical vapor deposition system. The stress and hence the curvature of the films on Si substrates can be varied and controlled by changing the BCD. We propose applications for such stressed films in the areas in which bent crystals are being used for various purposes, i.e., particle physics, x-ray optics, etc. These bent Si substrates can replace crystal benders, a cumbersome mechanical arrangement, used for bending Si in those areas. © 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
81.07.Bc Nanocrystalline materials
62.25.-g Mechanical properties of nanoscale systems
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Spectral profile of the two-photon absorption coefficients in CaF2 and BaF2

Toru Tsujibayashi, Koichi Toyoda, Shiro Sakuragi, Masao Kamada, and Minoru Itoh

Appl. Phys. Lett. 80, 2883 (2002); http://dx.doi.org/10.1063/1.1471939 (3 pages) | Cited 15 times

Online Publication Date: 16 April 2002

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Two-photon absorption spectra due to the valence excitons in CaF2 and BaF2 have been measured using the second harmonic of the output of a XeCl-excimer-laser pumped dye laser as a light source. The band gap energies of CaF2 and BaF2 are obtained as 11.8 and 10.6 eV at 298 K, respectively. The two-photon absorption coefficient β in the spectral region below the 2P exciton is expressed by an exponential function of the photon energy in both crystals. The values of β at the 2P exciton peak are about 2×10−9 cm/W for CaF2 and 3×10−9 cm/W for BaF2. © 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)
71.20.Ps Other inorganic compounds
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Control of the polarity of molecular-beam-epitaxy-grown GaN thin films by the surface nitridation of Al2O3 (0001) substrates

S. Mikroulis, A. Georgakilas, A. Kostopoulos, V. Cimalla, E. Dimakis, and Ph. Komninou

Appl. Phys. Lett. 80, 2886 (2002); http://dx.doi.org/10.1063/1.1472481 (3 pages) | Cited 19 times

Online Publication Date: 16 April 2002

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The nitridation of Al2O3 (0001) substrate surfaces by radio-frequency nitrogen plasma has been investigated. A 1.5-nm-thick surface nitride layer occurred for 100 min nitridation at high substrate temperature, while the nitridation appeared to be limited to a surface atomic plane at low temperature. In-plane lattice constant relaxation was observed in both cases. A high nitridation temperature resulted into a Ga face and a low temperature to N-face polarity of overgrown GaN films. However, low temperature nitridation and an AlN buffer layer also produced a Ga-face polarity. The results are consistent with low formation energy of AlN/sapphire films with Ga-face polarity. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Surface segregation of bulk oxygen on oxidation of epitaxially grown Nb-doped SrTiO3 on SrTiO3(001)

Fan Chen, Tong Zhao, Y. Y. Fei, Huibin Lu, Zhenghao Chen, Guozhen Yang, and X. D. Zhu

Appl. Phys. Lett. 80, 2889 (2002); http://dx.doi.org/10.1063/1.1473694 (3 pages) | Cited 17 times

Online Publication Date: 16 April 2002

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We studied the epitaxy of 10 mol % Nb:SrTiO3 on a SrTiO3(100) substrate under an interrupted pulsed-laser-deposition condition. By monitoring the recovery behaviors of reflection high-energy electron diffraction intensity and an optical reflectance difference signal from the growth surface, we observed that, at temperatures above 630 °C, the oxidation of an as-deposited Nb:SrTiO3 monolayer was achieved by the diffusion of oxygen vacancies in the monolayer into the substrate. © 2002 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.Dv Composition, segregation; defects and impurities
81.65.Mq Oxidation
81.15.Fg Pulsed laser ablation deposition

Vaporization thermodynamics of MgB2 and MgB4

S. Brutti, A. Ciccioli, G. Balducci, G. Gigli, P. Manfrinetti, and A. Palenzona

Appl. Phys. Lett. 80, 2892 (2002); http://dx.doi.org/10.1063/1.1471382 (3 pages) | Cited 27 times

Online Publication Date: 16 April 2002

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The vaporization behavior of MgB2 and MgB4 under thermodynamic conditions has been studied by the Knudsen effusion-mass spectrometry technique. In the temperature range explored (883–1154 K), magnesium borides are observed to decompose by loss of gaseous Mg only. The equilibrium pressures of Mg(g) have been measured during high-temperature decompositions involving MgB2/MgB4 and MgB4/MgB7 two-phase mixtures and the corresponding standard reaction enthalpies were determined. The decomposition temperatures for MgB2 and MgB4 were also inferred by the relevant Van’t Hoff plots. © 2002 American Institute of Physics.
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64.70.Hz Solid-vapor transitions
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
65.40.G- Other thermodynamical quantities
82.60.Cx Enthalpies of combustion, reaction, and formation
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