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4 Sep 2000

Volume 77, Issue 10, pp. 1413-1560

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Probing the near fields of the super-resolution near-field optical structure

Din Ping Tsai and Wei Chih Lin

Appl. Phys. Lett. 77, 1413 (2000); http://dx.doi.org/10.1063/1.1290692 (3 pages) | Cited 36 times

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Super-resolution near-field structure, glass/SiN (170 nm)/Sb (15 nm)/SiN (20 nm), a promising structure for near-field ultrahigh-density optical data storage, has been studied by a tapping-mode tuning-fork near-field scanning optical microscope in transmission mode. Both propagating and evanescent field intensities were found at the focused spots of the surface of the super-resolution near-field structure. Images of the near-field intensity gradients at different excited laser powers (0.42–2.43 μW) showed that the area of the static evanescent intensity could be stably controlled. The enhancement of the near-field intensity, and the reduction of the focused spot through the super-resolution near-field structure, glass/SiN (170 nm)/Sb (15 nm)/SiN (20 nm) have been observed. © 2000 American Institute of Physics.
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42.70.Ce Glasses, quartz
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
42.79.Vb Optical storage systems, optical disks
42.79.Wc Optical coatings
42.65.-k Nonlinear optics

Electroluminescence from semitransparent Au film/nanometer SiO2/nanometer Si/nanometer SiO2/n+–Si structure under reverse bias

C. L. Heng, Y. K. Sun, S. T. Wang, Y. Chen, Y. P. Qiao, B. R. Zhang, Z. C. Ma, W. H. Zong, and G. G. Qin

Appl. Phys. Lett. 77, 1416 (2000); http://dx.doi.org/10.1063/1.1290597 (3 pages) | Cited 4 times

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Nanometer SiO2/nanometer Si/nanometer SiO2 double-barrier (DB) structures, with Si layers having eleven different thicknesses from 2 to 4 nm, were deposited on n+–Si substrates using the magnetron sputtering technique. Strong electroluminescence (EL) from semitransparent Au film/DB/n+–Si structure was observed under reverse bias in a range of about 5–7 V. It is found that every EL spectrum of the structure can be decomposed into two Gaussian bands with peaks at around 1.85 and 2.25 eV, and their intensities and current swing synchronously with increasing nanometer Si layer thickness; the periodic length of swing is consistent with half of the de Broglie wavelength of the carriers. A comparison was carried out between EL from the Au/DB/n+–Si structure under reverse bias and that from the Au/DB/p–Si structure under forward bias reported previously. © 2000 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Bz Metals and metallic alloys

Highly efficient GaInAs/(Al)GaAs quantum-dot lasers based on a single active layer versus 980 nm high-power quantum-well lasers

F. Klopf, J. P. Reithmaier, and A. Forchel

Appl. Phys. Lett. 77, 1419 (2000); http://dx.doi.org/10.1063/1.1290601 (3 pages) | Cited 28 times

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Highly efficient 980 nm GaInAs/(Al)GaAs quantum-dot (QD) and quantum-well (QW) lasers based on a single active layer have been fabricated and compared in view of high-power applications. QD lasers show a significantly reduced temperature shift of the emission wavelength and achieve external quantum efficiencies of 80% (>1 W/A for 1-mm-long devices). For longer cavity lengths (>2.5 mm), QD lasers show lower threshold current densities than QW lasers. Threshold current densities as low as 54 A/cm2 are reached. © 2000 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.)
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Monolithic photorefractive molecule with excellent transparency in the visible region

Jiwon Sohn, Jaehoon Hwang, Soo Young Park, Jin-Kyung Lee, Jai-Hyung Lee, Joon-Sung Chang, Geon Joon Lee, Bo Zhang, and Qihuang Gong

Appl. Phys. Lett. 77, 1422 (2000); http://dx.doi.org/10.1063/1.1290727 (3 pages) | Cited 12 times

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9-(2-Ethyl-hexyl)-3-[2-(4-methanesulfonyl-phenyl)vinyl]-9H-carbazole (EHCS) was synthesized as a monolithic photorefractive molecule forming low Tg( ∼ 25 °C) organic glass. It showed distinct photoconductivity due to the carbazole moiety and the optical nonlinearity by the push–pull structure. The EHCS glass showed excellent optical quality and great stability as the ethylhexyl group effectively suppressed the crystallization in the films. Also, the extremely simple structure of EHCS contributed to a very high chromophore concentration. This single-component photorefractive glass of EHCS showed large net gain (56.3 cm−1) and diffraction efficiency (12%). Photorefractivity of EHCS glass was greatly improved by doping with a small amount (<1%) of 2,4,7-trinitrofluorenone (TNF). The two-beam coupling gain of samples with TNF was 113 cm−1 and the diffraction efficiency was 29%. © 2000 American Institute of Physics.
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42.70.Ln Holographic recording materials; optical storage media
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)
42.70.Jk Polymers and organics
42.70.Ce Glasses, quartz
72.40.+w Photoconduction and photovoltaic effects
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.66.Qn Polymers; organic compounds

Effect of grain boundaries on carrier lifetime in chemical-vapor-deposited diamond film

Hitoki Yoneda, Kazutatsu Tokuyama, Riichi Yamazaki, Ken-ichi Ueda, Hironori Yamamoto, and Kazuhiro Baba

Appl. Phys. Lett. 77, 1425 (2000); http://dx.doi.org/10.1063/1.1308054 (3 pages) | Cited 2 times

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Using the reflective measurements, the effect of grain boundaries on the lifetime of photogenerated carriers was investigated for chemical-vapor-deposited (CVD) diamond films. To investigate the effect of grain boundaries on the carrier dynamics, photons having energy lower than the band gap energy of a single crystal of diamond were used for pumping. For a 4.8 eV photon, the measured lifetime was several tens of picoseconds, and that was consistent with photoconductive current measurements. However, a dramatic decrease of the carrier lifetime was observed in the case of 3.2 eV irradiation. The variation of the lifetime inside the single grain was measured by a microscopic pump–probe method. The carrier lifetime near the grain boundary decreased from 5 to 8 ps at the center to 0.35–0.5 ps. This decreased lifetime and the carrier generation efficiency with lower energy photon had a negative correlation. To explain this mechanism, we considered the decrease in lifetime to be related to the density of the imperfection or mid-band gap states inside the single-CVD-polycrystalline grain. © 2000 American Institute of Physics.
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73.61.Cw Elemental semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.72.Mm Grain and twin boundaries
73.50.Pz Photoconduction and photovoltaic effects

How a quantum-dot laser turns on

Marius Grundmann

Appl. Phys. Lett. 77, 1428 (2000); http://dx.doi.org/10.1063/1.1290716 (3 pages) | Cited 16 times

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The turn-on dynamics of quantum-dot lasers is modeled theoretically. The impact of the—so far technologically inevitable—inhomogeneous broadening σ, the homogeneous broadening Γ, and the interlevel relaxation time on the relaxation oscillations (ROs) is investigated. When the inhomogeneous broadening is dominant (Γ≪σ), the individual nanostructures in the ensemble exhibit independent ROs. In the case of significant homogeneous (Γ ≥ σ) broadening, the quantum-dot ensemble exhibits collective, synchronized ROs, leading to a stronger intensity modulation and a larger turn-on delay. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.60.Rn Relaxation oscillations and long pulse operation
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Infrared absorption peak due to Ta=O bonds in Ta2O5 thin films

Haruhiko Ono and Ken-ichi Koyanagi

Appl. Phys. Lett. 77, 1431 (2000); http://dx.doi.org/10.1063/1.1290494 (3 pages) | Cited 20 times

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Ta2O5 films deposited on Si substrates were investigated using transmission Fourier-transform infrared spectroscopy. We found a new absorption peak at 2340 cm−1 that can be characterized as a stretching vibration mode due to Ta=O bonds in the films. This peak appeared following annealing in O2 ambient, but not in N2 ambient. It was located at 2335 cm−1 in amorphous Ta2O5 films and shifted to 2340 cm−1 after crystallization by annealing at over 700 °C. The bonds associated with the peak were homogeneously distributed in the film. We demonstrated that Ta2O5 films can include strong double bonds between Ta and O (Ta=O) in the structure, independent of whether they are crystalline or amorphous. © 2000 American Institute of Physics.
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78.66.Nk Insulators
68.55.-a Thin film structure and morphology
61.50.Lt Crystal binding; cohesive energy
78.30.Hv Other nonmetallic inorganics

Thermal expansion of bulk and homoepitaxial GaN

V. Kirchner, H. Heinke, D. Hommel, J. Z. Domagala, and M. Leszczynski

Appl. Phys. Lett. 77, 1434 (2000); http://dx.doi.org/10.1063/1.1290491 (3 pages) | Cited 13 times

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The thermal behavior of Mg-doped and intentionally undoped bulk crystals and homoepitaxial GaN was investigated in a wide temperature range from 12 to 600 K. With high-resolution x-ray diffraction, both lattice parameters a and c were determined and the thermal expansion coefficients were calculated. Within the experimental accuracy, mean values were extracted for the temperature ranges 12–100, 100–250, and 250–600 K. These values are essential, especially, for the interpretation of measurements of other GaN properties performed at low temperatures. © 2000 American Institute of Physics.
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65.40.De Thermal expansion; thermomechanical effects
68.60.Dv Thermal stability; thermal effects
61.66.Fn Inorganic compounds
68.55.-a Thin film structure and morphology

Effect of oxidation and reoxidation on the oxide-substrate interface of 4H- and 6H-SiC

G. G. Jernigan, R. E. Stahlbush, and N. S. Saks

Appl. Phys. Lett. 77, 1437 (2000); http://dx.doi.org/10.1063/1.1290490 (3 pages) | Cited 23 times

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X-ray photoelectron spectroscopy and sputter depth profiling were used to investigate SiO2 grown on 4H- and 6H-SiC with and without a reoxidation procedure. The oxides grown and oxide-substrate interfaces formed on 4H and 6H were similar in chemistry but different from Si(100). Reoxidation changes the structure of the oxide and the abruptness of the oxide-substrate interface. We propose a model for SiC oxidation where a transition layer containing Si–Si bonds is produced between the oxide and the SiC substrate.
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81.65.Mq Oxidation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.35.Ct Interface structure and roughness
79.60.Jv Interfaces; heterostructures; nanostructures
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.20.-r Electron states at surfaces and interfaces

Biphotonic holographic gratings in azobenzene polyesters: Surface relief phenomena and polarization effects

C. Sánchez, R. Alcalá, S. Hvilsted, and P. S. Ramanujam

Appl. Phys. Lett. 77, 1440 (2000); http://dx.doi.org/10.1063/1.1290604 (3 pages) | Cited 17 times

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Biphotonic holographic gratings have been recorded in a side-chain azobenzene liquid crystalline polyester using a blue incoherent source and a He–Ne laser. Intensity gratings and the appearance of surface relief have been observed when two linearly polarized beams from a He–Ne laser are made to interfere on a film illuminated with blue light. Polarized holographic gratings are also created with two orthogonally circularly polarized He–Ne beams. All these gratings are stable in darkness but can be erased with blue light. © 2000 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Jk Polymers and organics
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.25.H- Macromolecular and polymers solutions; polymer melts
61.30.-v Liquid crystals

Reaction of Co and capping layers and its effect on CoSi2 formation in Si/SiOx/Co system

Gi Bum Kim, Joon Seop Kwak, Hong Koo Baik, Sung Man Lee, Sang Ho Oh, and Chan Gyung Park

Appl. Phys. Lett. 77, 1443 (2000); http://dx.doi.org/10.1063/1.1290689 (3 pages) | Cited 4 times

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The role of the reaction between the capping layer and Co on the crystalline nature of CoSi2 films in refractory metal-capped Si/SiOx/Co system has been investigated. The epitaxial CoSi2 film was obtained in the capping layers (Ti, Zr) with high tendency of mixing between Co and the capping layer. Amorphous Ti–Co layer was produced at 450 °C, and its thickness was increased at 550 °C. The formation of amorphous Ti–Co layer during low-temperature annealing may be responsible for the formation of epitaxial CoSi2. Meanwhile, the polycrystalline CoSi2 was formed in the capping layer (Cr, Mo) with low tendency of mixing. These results can be explained by the fact that the mixing layer formed from the reaction between Co and refractory metal control the Co diffusion to the Si substrate as well as the thin SiOx between Co and Si. © 2000 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing

Coupling of kinetic and transport phenomena in self-organization of C–B–N nanotube growth into sandwich structures

Oleg A. Louchev, Yoichiro Sato, Hisao Kanda, and Yoshio Bando

Appl. Phys. Lett. 77, 1446 (2000); http://dx.doi.org/10.1063/1.1290600 (3 pages) | Cited 8 times

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A mechanism for self-organization of C–B–N sandwich-like nanotubes with well-separated phases of C and BN [K. Suenaga, C. Colliex, N. Demoncy, A. Loiseau, H. Pascard, F. Willaime, Science 278, 653 (1997)] in arc-discharge is proposed. This mechanism includes (i) the microkinetic self-organization of nanotube growth in step-flow mode combined with a C and BN phase segregation at growth steps and (ii) the self-organization of “macro”-oscillations of impinging fluxes of C and B on the surface of nanotubes, which are caused by the nonuniformity of C and B content in the gas combined with the onset of natural convection, providing repeated transport of emerging nanotubes through regions with abundance in C and B, and leading to nucleation and growth of C and BN layers. © 2000 American Institute of Physics.
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81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Growth of step-free surfaces on device-size (0001)SiC mesas

J. Anthony Powell, Philip G. Neudeck, Andrew J. Trunek, Glenn M. Beheim, Lawrence G. Matus, Richard W. Hoffman, and Luann J. Keys

Appl. Phys. Lett. 77, 1449 (2000); http://dx.doi.org/10.1063/1.1290717 (3 pages) | Cited 36 times

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It is believed that atomic-scale surface steps cause defects in single-crystal films grown heteroepitaxially on SiC substrates. A method is described whereby surface steps can be grown out of existence on arrays of device-size mesas on commercial “on-axis” SiC wafers. Step-free mesas with dimensions up to 200 μm square have been produced on 4H-SiC wafers and up to 50 μm square on a 6H-SiC wafer. A limiting factor in scaling up the size and yield of the step-free mesas is the density of screw dislocations in the SiC wafers. The fundamental significance of this work is that it demonstrates that two-dimensional nucleation of SiC can be suppressed while carrying out step-flow growth on (0001)SiC. The application of this method should enable the realization of improved heteroepitaxially-grown SiC and GaN device structures. © 2000 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations

Temperature dependence of the transition from two-dimensional to three-dimensional growth of Ge on (001)Si studied by reflection high-energy electron diffraction

V. Cimalla and K. Zekentes

Appl. Phys. Lett. 77, 1452 (2000); http://dx.doi.org/10.1063/1.1290720 (3 pages) | Cited 8 times

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Germanium islands have been grown on Si(001) by solid-source molecular-beam epitaxy at temperatures between 325 and 900 °C. The formation of metastable {105} faceted clusters and macroislands was investigated by real-time reflection high-energy electron diffraction. Up to 600 °C, the two-dimensional (2D)-three-dimensional (3D) growth transition through the formation of hut clusters appears at a temperature-independent critical thickness, while the coalescence to macroislands is thermally activated. An activation barrier was also found for the 2D–3D growth transition directly to macroislands at growth temperatures above 600 °C. The crossing of the two competing transitions at 600 °C determines the two growth regimes. © 2000 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Ion-beam-induced porosity of GaN

S. O. Kucheyev, J. S. Williams, C. Jagadish, J. Zou, V. S. J. Craig, and G. Li

Appl. Phys. Lett. 77, 1455 (2000); http://dx.doi.org/10.1063/1.1290722 (3 pages) | Cited 41 times

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Wurtzite GaN films bombarded with heavy ions (197Au+) show anomalous swelling of the implanted region with corresponding volume expansion up to ∼ 50%. Results show that this phenomenon is due to the formation of a porous layer of amorphous GaN. An important implication of this study for the fabrication of GaN-based devices is that amorphization of GaN should be avoided during ion implantation. © 2000 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.uj III-V and II-VI semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys

Maximized sp3 bonding in carbon nitride phases

S. E. Rodil, W. I. Milne, J. Robertson, and L. M. Brown

Appl. Phys. Lett. 77, 1458 (2000); http://dx.doi.org/10.1063/1.1308273 (3 pages) | Cited 22 times

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Carbon nitride films were deposited using a low pressure, dual ion beam system consisting of a filtered cathodic vacuum arc and a plasma beam source for carbon and nitrogen ions, respectively. This system maintains highly ionized beams even at high nitrogen fluxes, unlike in single beam systems. Film composition and bonding were measured by electron energy loss spectroscopy. Films with nitrogen to carbon atom ratios (N/C) up to 0.5 are produced. The carbon bonding is found to change gradually from sp3 to sp2, rather than sharply above a critical N content, as found previously. This indicates that N atoms form individual C�N bonds rather than causing a reversion of the entire C network to sp2. This allows us to maintain C sp3 bonding to the highest N contents so far achieved. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
79.20.Kz Other electron-impact emission phenomena
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Observation and first-principles calculation of buried wurtzite phases in zinc-blende CdTe thin films

Y. Yan, M. M. Al-Jassim, K. M. Jones, S.-H. Wei, and S. B. Zhang

Appl. Phys. Lett. 77, 1461 (2000); http://dx.doi.org/10.1063/1.1308062 (3 pages) | Cited 17 times

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We report direct observation of the existence of buried thin wurtzite CdTe layers in nominally pure zinc-blende CdTe thin films using high-resolution transmission electron microscopy. The formation of the buried wurtzite layers is a result of the formation of high density of planar defects in the zinc-blende films—the wurtzite layers are formed by closely spaced lamellar twins. First-principles calculations reveal that the presence of the buried wurtzite layers may be responsible for the poor electrical properties of the polycrystalline zinc-blende CdTe films. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Thermal conductivity of fully and partially coalesced lateral epitaxial overgrown GaN/sapphire (0001) by scanning thermal microscopy

D. I. Florescu, V. M. Asnin, Fred H. Pollak, A. M. Jones, J. C. Ramer, M. J. Schurman, and I. Ferguson

Appl. Phys. Lett. 77, 1464 (2000); http://dx.doi.org/10.1063/1.1308057 (3 pages) | Cited 45 times

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We have measured high spatial/depth resolution (∼2–3 μm) thermal conductivity (κ) at 300 K of both fully and partially coalesced GaN/sapphire (0001) samples fabricated by lateral epitaxial overgrowth. On the fully coalesced sample we found 1.86W/cm K<κ<2.05 W/cm K over a distance of approximately 50 μm. One of the partially coalesced samples had 2.00 W/cm K<κ<2.10 W/cm K on the overgrown regions, as identified by atomic force microscopy imaging. These latter results are the highest thermal conductivity values reported on GaN material. A correlation between low threading dislocation density and high thermal conductivity values was established. © 2000 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
68.55.-a Thin film structure and morphology
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

High-energy-resolution scintillator: Ce3+ activated LaCl3

E. V. D. van Loef, P. Dorenbos, C. W. E. van Eijk, K. Krämer, and H. U. Güdel

Appl. Phys. Lett. 77, 1467 (2000); http://dx.doi.org/10.1063/1.1308053 (2 pages) | Cited 61 times

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The scintillation properties of LaCl3 doped with 10% Ce3+ are presented. Under optical and gamma ray excitation, Ce3+ emission is observed to peak at 330 and 352 nm. The scintillation light output is 46 000±1000 photons/MeV at 662 keV. Forty percent is emitted with a decay time of 26 ns, 30% with 210 ns, and 30% with about 1000 ns. An energy resolution (full width at half maximum over the peak position) of 3.3±0.3% was observed for the 662 keV full absorption peak. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials

Paramagnetic defects at the interface of ultrathin oxides grown under vacuum ultraviolet photon excitation on (111) and (100) Si

A. Stesmans and V. V. Afanas’ev

Appl. Phys. Lett. 77, 1469 (2000); http://dx.doi.org/10.1063/1.1289265 (3 pages) | Cited 20 times

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Electron-spin-resonance monitoring of Si dangling-bond-type interface defects is used to study ultrathin (∼20 Å) Si-oxide films grown by vacuum ultraviolet (VUV)-enhanced oxidation of Si at 300 K. Large densities (up to ∼ 9×1012 cm−2) of Pb and Pb0 centers (interfacial Si3�Si⋅) are observed in VUV-grown (111) and (100) Si/SiO2, respectively. As compared to standard thermal Si/SiO2, two major differences emerge: the VUV Si/SiO2 interface is under substantially enhanced stress, while no Pb1 defects are discerned in VUV (100) Si/SiO2. It is inferred that Pb1 generation requires a minimum amount of oxide relaxation. Microscopic understanding is provided for the known inferior electrical interface quality threatening low-thermal-budget oxide fabrication. © 2000 American Institute of Physics.
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68.35.Ct Interface structure and roughness
81.05.Cy Elemental semiconductors
81.65.Mq Oxidation
82.50.-m Photochemistry
76.30.Mi Color centers and other defects
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.35.Gy Mechanical properties; surface strains
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Photovoltaic and spectral photoresponse characteristics of n-C/p-C solar cell on a p-silicon substrate

K. M. Krishna, M. Umeno, Y. Nukaya, T. Soga, and T. Jimbo

Appl. Phys. Lett. 77, 1472 (2000); http://dx.doi.org/10.1063/1.1290687 (3 pages) | Cited 35 times

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Recent studies have shown the application of amorphous carbon as a semiconductor in C/Si heterojunction photovoltaic solar cells. In this letter, we report the rectifying current–voltage characteristics of the phosphorus-doped carbon/undoped-carbon (n-C/p-C) junction. The p- and n-carbon films were deposited by pyrolysis and ion-beam sputtering, respectively, on a p-Si substrate, using camphor as a natural carbon precursor. The preliminary photovoltaic characteristics of the cell reveals a short-circuit current density of 17.1 mA/cm2, open-circuit voltage of 0.339 V, and photoelectrical conversion efficiency of 1.82%, a reproducible result, under air mass zero and 1 sun illumination conditions. The spectral photoresponse characteristics of the cell of the above configuration was explained in terms of transmission/absorption characteristics of the two individual carbon layers. © 2000 American Institute of Physics.
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84.60.Jt Photoelectric conversion
81.15.Cd Deposition by sputtering
81.05.Cy Elemental semiconductors
73.61.Cw Elemental semiconductors
78.66.Db Elemental semiconductors and insulators

Bilayer quantum transistor

Can-Ming Hu and Detlef Heitmann

Appl. Phys. Lett. 77, 1475 (2000); http://dx.doi.org/10.1063/1.1290695 (3 pages) | Cited 9 times

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The ballistic transport properties of a bilayer structure are studied under the Landau–Büttiker formalism. An oscillatory conductance as a function of the front gate is found. The effect arises from the tunneling, which causes a phase difference between the symmetric and antisymmetric eigenstates. The gate electrode controls the effective tunneling gap and, therefore, the interference. The mechanism may be used to design a bilayer analogue of the spin field-effect transistor without ferromagnetic electrodes. © 2000 American Institute of Physics.
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85.35.Ds Quantum interference devices
73.23.Hk Coulomb blockade; single-electron tunneling

Electrical characterization of TiC ohmic contacts to aluminum ion implanted 4H–silicon carbide

S.-K. Lee, C.-M. Zetterling, E. Danielsson, M. Östling, J.-P. Palmquist, H. Högberg, and U. Jansson

Appl. Phys. Lett. 77, 1478 (2000); http://dx.doi.org/10.1063/1.1290690 (3 pages) | Cited 9 times

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We report on the investigation of epitaxial TiC ohmic contacts to Al ion implanted 4H–SiC. TiC ohmic contacts were formed by coevaporation of Ti and C60 at low temperature (<500 °C). A sacrificial silicon nitride (Si3N4) layer was deposited on the silicon carbide substrate prior to Al implantation in order to reach a high Al dopant concentration at the surface while maintaining a low dose. The combination of epitaxially grown TiC and the silicon nitride layer resulted in a promising scheme to make low resistivity ohmic contacts. The lowest contact resistivity (ρC) and sheet resistance (Rs) of the implanted layer at 25 °C were as low as 2×10−5 Ω cm2 and 0.6 kΩ/□, respectively. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
61.72.up Other materials
73.40.Cg Contact resistance, contact potential
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Temperature-dependent carrier trapping processes in short period quantum wire superlattices grown by flow rate modulation epitaxy

X. Q. Liu, A. Sasaki, N. Ohno, Xue-Lun Wang, and Mutsuo Ogura

Appl. Phys. Lett. 77, 1481 (2000); http://dx.doi.org/10.1063/1.1290693 (3 pages) | Cited 7 times

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We report the first systematic investigation of the temperature-dependent carrier transferring processes of very short period V-grooved GaAs/AlGaAs quantum wire superlattice structures grown by flow rate-modulated metal-organic vapor phase epitaxy. The one monolayer (1 ML) fluctuation causes carrier confinement in sidewall (111) facet superlattice structures, and is shown to play an important role in the carrier transferring process. At low temperatures, the carrier transfer is blocked by the barriers of 1 ML fluctuation, while at high temperatures the carrier transfer from (111) superlattice to the wire region is shown to be very efficient after thermally overcoming the barriers. The temperature-dependent decay times of the different parts give direct evidence of the carrier transferring process, which demonstrates that the carriers can trap into the wire region within 50 ps at temperatures higher than 100 K. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.55.Cr III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors

Electronic structures of polycrystalline ZnO thin films probed by electron energy loss spectroscopy

H. C. Ong, J. Y. Dai, K. C. Hung, Y. C. Chan, R. P. H. Chang, and S. T. Ho

Appl. Phys. Lett. 77, 1484 (2000); http://dx.doi.org/10.1063/1.1290596 (3 pages) | Cited 10 times

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The microstructure of polycrystalline ZnO thin films grown on amorphous fused quartz has been studied by transmission electron microscopy and electron energy loss spectroscopy (EELS). The optical functions of the grain and grain boundary of ZnO acquired from EELS are compared to elucidate the mechanism of the formation of self-assemble laser cavities within this material. It is found that the refractive index of the grain boundary is significantly lower than that of the grain due to the lack of excitonic resonance. This large refractive index difference between the grain and grain boundary substantiates the scenario that the formation of laser cavities is caused by the strong optical scattering facilitated in a highly disordered crystalline structure. In addition, our results also imply that the optical characteristics of ZnO have very high tolerance on defects. © 2000 American Institute of Physics.
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71.20.Nr Semiconductor compounds
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
79.20.Kz Other electron-impact emission phenomena
78.66.Hf II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.Mm Grain and twin boundaries
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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