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3 Sep 2001

Volume 79, Issue 10, pp. 1411-1578

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Two-photon photopolymerization and diagnosis of three-dimensional microstructures containing fluorescent dyes

Hong-Bo Sun, Tomokazu Tanaka, Kenji Takada, and Satoshi Kawata

Appl. Phys. Lett. 79, 1411 (2001); http://dx.doi.org/10.1063/1.1399312 (3 pages) | Cited 38 times

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We report in this letter two-photon-absorption photopolymerization using fluorescent dye-doped resin, by which complex fluorescence-active three-dimensional (3D) microstructures were readily produced. Structures were imaged by means of two-photon confocal techniques. The realization of dye-doping photopolymerization would be an important step towards production of photonic-crystal-based high-efficiency polymer optoelectronic devices. Furthermore, we found that the doped dye acted as label molecules to stain solidified structures, which provided an effective two-photon fluorescence technique for internal microdiagnosis of polymerized 3D microstructures. © 2001 American Institute of Physics.
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82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry
78.55.Kz Solid organic materials

Room-temperature lasing of InGaN multiquantum-well hexagonal microfacet lasers by current injection

Tetsuya Akasaka, Seigo Ando, Toshio Nishida, Hisao Saito, and Naoki Kobayashi

Appl. Phys. Lett. 79, 1414 (2001); http://dx.doi.org/10.1063/1.1398322 (3 pages) | Cited 6 times

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InGaN multiquantum-well (MQW) hexagonal microfacet (HMF) lasers have been fabricated by electron cyclotron resonance dry etching of as-grown planar InGaN MQW laser structures followed by metalorganic vapor phase epitaxy regrowth of p-GaN to form mirror facets of the lasers. The mirror facets are smooth and vertical {11math0} facets of the regrown p-GaN. The HMF lasers lase at 401 nm under pulsed operation at room temperature. There is no significant difference in threshold current density for different cavity lengths of 480 and 770 μm, indicating that the mirror facets act as total reflectors. © 2001 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Bh Lenses, prisms and mirrors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.St Quantum wells

Gain mechanism in GaN Schottky ultraviolet detectors

O. Katz, V. Garber, B. Meyler, G. Bahir, and J. Salzman

Appl. Phys. Lett. 79, 1417 (2001); http://dx.doi.org/10.1063/1.1394717 (3 pages) | Cited 78 times

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Schottky barrier GaN ultraviolet detectors, both in vertical and in lateral configuration, as well as in a metal–semiconductor–metal geometry were implemented. All devices exhibit a high gain at both reverse and forward bias. The photoresponse in the forward bias is in the positive current direction. We attribute the gain to trapping of minority carriers at the semiconductor–metal interface. The excellent agreement between the calculated responsivity and the experiment indicates that the model is valid for all device structures under study, and represents a unified description of gain mechanism in GaN Schottky detectors. © 2001 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.40.Sx Metal-semiconductor-metal structures
73.40.Ns Metal-nonmetal contacts
73.20.-r Electron states at surfaces and interfaces

Evolution of anisotropic reflection gratings formed in holographic polymer-dispersed liquid crystals

R. L. Sutherland, V. P. Tondiglia, L. V. Natarajan, and T. J. Bunning

Appl. Phys. Lett. 79, 1420 (2001); http://dx.doi.org/10.1063/1.1399303 (3 pages) | Cited 32 times

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The temporal evolution of an anisotropic reflection grating produced in a holographic polymer-dispersed liquid crystal film is investigated. We find that this type of grating is preceded in time by an isotropic concentration grating, and that the development of the anisotropic grating can be delayed until several seconds after laser exposure. The formation of an anisotropic grating is nearly coincident with the onset of phase separation of liquid crystal and implies a macroscopic ordering of liquid crystal droplet directors. Detailed knowledge of grating evolution may allow in situ control over the polarization sensitivity of the hologram. © 2001 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
64.75.-g Phase equilibria
61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems

Fixing solitonic y junctions in photorefractive strontium–barium–niobate

Matthew Klotz, Mike Crosser, Aqiang Guo, Michael Henry, Gregory J. Salamo, Mordechai Segev, and Gary L. Wood

Appl. Phys. Lett. 79, 1423 (2001); http://dx.doi.org/10.1063/1.1389824 (3 pages) | Cited 3 times

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Two-dimensional solitonic orbital waveguides as y junctions were formed in a strontium barium niobate crystal. The waveguides are 10–20 μm in diameter and propagate unpolarized light. © 2001 American Institute of Physics.
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42.65.Tg Optical solitons; nonlinear guided waves
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers

Optical transparency of metallic La0.5Sr0.5TiO3+δ thin films

J. H. Cho and H. J. Cho

Appl. Phys. Lett. 79, 1426 (2001); http://dx.doi.org/10.1063/1.1402961 (3 pages) | Cited 22 times

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We prepared for Mott–Hubbard-type perovskite La0.5Sr0.5TiO3+δ thin films under an oxygen reduced environment, 5% H2/Ar. Control of the partial pressure during deposition could change the conductivity of the films, and induces a metal–insulator transition. In addition, we observed an excellent transparency at visible light with a metallic behavior, where this property could be utilized as a transparent conductor. © 2001 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)
71.30.+h Metal-insulator transitions and other electronic transitions
78.66.Bz Metals and metallic alloys
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Depth dependence of {311} defect dissolution

V. C. Venezia, R. Kalyanaraman, H.-J. L. Gossmann, C. S. Rafferty, and P. Werner

Appl. Phys. Lett. 79, 1429 (2001); http://dx.doi.org/10.1063/1.1392972 (3 pages) | Cited 13 times

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A deep band of {311} defects was created 520 nm below the silicon surface with a 350 keV Si implant followed by a cluster-forming rapid thermal anneal (800 °C, 1000 s). Chemical etching was used to vary the depth to the surface of the {311}-defect band. Afterwards, the defect dissolution was investigated at 750 °C for different times. Varying the depth in this fashion assures that only the depth and no other feature of the cluster distribution is changed. The {311} defects were analyzed by plan-view, transmission electron microscopy. We show that the dissolution time of the {311}-defect band varies linearly with depth, confirming that surface recombination controls the dissolution and is consistent with analogous observations of transient enhanced diffusion. © 2001 American Institute of Physics.
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71.55.Cn Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
61.72.J- Point defects and defect clusters
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.80.Jh Ion radiation effects
81.65.Cf Surface cleaning, etching, patterning
73.25.+i Surface conductivity and carrier phenomena
81.05.Cy Elemental semiconductors
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Interpretation of double x-ray diffraction peaks from InGaN layers

S. Pereira, M. R. Correia, E. Pereira, K. P. O’Donnell, E. Alves, A. D. Sequeira, and N. Franco

Appl. Phys. Lett. 79, 1432 (2001); http://dx.doi.org/10.1063/1.1397276 (3 pages) | Cited 32 times

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The presence of two, or more, x-ray diffraction (XRD) peaks from an InGaN epilayer is sometimes regarded as an indicator of phase segregation. Nevertheless, detailed characterization of an InGaN/GaN bilayer by a combination of XRD and Rutherford backscattering spectrometry (RBS) shows that splitting of the XRD peak may be completely unrelated to phase decomposition. Wurtzite InGaN/GaN layers were grown in a commercial reactor. An XRD reciprocal space map performed on the (105) plane shows that one component of the partially resolved InGaN double peak is practically aligned with that of the GaN buffer, indicating that part of the layer is pseudomorphic to the GaN template. The other XRD component is shown to have the same indium content as the pseudomorphic component, from a consideration of the effect of strain on the c- and a-lattice constants. The composition deduced from XRD measurements is confirmed by RBS. Depth-resolving RBS channeling angular scans also show that the region closer to the GaN/InGaN interface is nearly pseudomorphic to the GaN substrate, whereas the surface region is almost fully relaxed. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
61.05.cp X-ray diffraction
64.75.-g Phase equilibria

Dependence of the emission wavelength on the internal electric field in quantum-dot laser structures grown by metal–organic chemical-vapor deposition

A. Passaseo, G. Maruccio, M. De Vittorio, S. De Rinaldis, T. Todaro, R. Rinaldi, and R. Cingolani

Appl. Phys. Lett. 79, 1435 (2001); http://dx.doi.org/10.1063/1.1400088 (3 pages) | Cited 6 times

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We show that the combination of different electric fields in In0.5Ga0.5As/GaAs quantum-dot electroluminescent devices dramatically blueshifts the emission wavelength even though the photoluminescence occurs at the expected value of 1.3 μm at room temperature. Systematic photoluminescence (PL), electroluminescence (EL), and photocurrent measurements demonstrate that the electric field associated with the built-in dipole in the dots, directed from the base of the dots to their apex, and the device junction field lead to the depletion of the ground state. As a consequence, structures grown on n-type GaAs substrates exhibit electroluminescence only from the excited states (whereas the photoluminescence comes from the ground level). Instead, by growing the same device structure on p-type GaAs substrates, i.e., by reversing the direction of the built-in electric field of the device, the effect of the permanent dipole is strongly reduced, thus allowing us to obtain EL emission at the designed wavelength of 1.3 μm at 300 K, coincident to the PL. This effect expands the possibilities for the achievement of efficient lasing in the spectral region of interest for optical transmission. The electric field associated to the dipole moment is estimated to be around 150 kV/cm. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.55.Cr III-V semiconductors
85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.Hc Quantum dots

Amorphous-iron disilicide: A promising semiconductor

M. Milosavljević, G. Shao, N. Bibić, C. N. McKinty, C. Jeynes, and K. P. Homewood

Appl. Phys. Lett. 79, 1438 (2001); http://dx.doi.org/10.1063/1.1400760 (3 pages) | Cited 24 times

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We report here the synthesis and the measurements of the microstructural and optical properties of a promising semiconductor, amorphous-iron disilicide. The material was obtained by ion-beam mixing of Fe layers on Si, with Ar8+ ions, at 300 °C. Optical absorption measurements indicate a semiconductor with a direct band gap of 0.88 eV. The significance of this discovery is that it demonstrates the existence of such a material. It should be possible to synthesize by other techniques and could be applied in large-area electronics. © 2001 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
61.43.Dq Amorphous semiconductors, metals, and alloys
66.30.Ny Chemical interdiffusion; diffusion barriers
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Synthesis and characterization of highly-conducting nitrogen-doped ultrananocrystalline diamond films

S. Bhattacharyya, O. Auciello, J. Birrell, J. A. Carlisle, L. A. Curtiss, A. N. Goyette, D. M. Gruen, A. R. Krauss, J. Schlueter, A. Sumant, and P. Zapol

Appl. Phys. Lett. 79, 1441 (2001); http://dx.doi.org/10.1063/1.1400761 (3 pages) | Cited 187 times

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Ultrananocrystalline diamond (UNCD) films with up to 0.2% total nitrogen content were synthesized by a microwave plasma-enhanced chemical-vapor-deposition method using a CH4(1%)/Ar gas mixture and 1%–20% nitrogen gas added. The electrical conductivity of the nitrogen-doped UNCD films increases by five orders of magnitude (up to 143 Ω−1 cm−1) with increasing nitrogen content. Conductivity and Hall measurements made as a function of film temperature down to 4.2 K indicate that these films have the highest n-type conductivity and carrier concentration demonstrated for phase-pure diamond thin films. Grain-boundary conduction is proposed to explain the remarkable transport properties of these films. © 2001 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
73.61.Cw Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
52.77.Dq Plasma-based ion implantation and deposition
61.72.Mm Grain and twin boundaries

Influence of dose rate and temperature on ion-beam-induced defect evolution in Si investigated by channeling implantation at different doses

M. Posselt, L. Bischoff, and J. Teichert

Appl. Phys. Lett. 79, 1444 (2001); http://dx.doi.org/10.1063/1.1396319 (3 pages) | Cited 11 times

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A focused ion beam system is applied to study the dose dependence of the shape of Ge channeling implantation profiles at two very different dose rates (1018 and 1011 cm−2 s−1), and for implantation temperatures of 250 °C and room temperature (RT). A simple model for the buildup of radiation damage is developed to describe the dechanneling effect of defects formed during ion bombardment. The use of this model in atomistic computer simulations yields Ge depth profiles which agree well with measured data. The lifetime of ion-beam-induced defects at 250 °C was estimated to be in the order of 100 s. At RT, some defect relaxation was found between 10 μs and 100 s after ion impact. © 2001 American Institute of Physics.
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61.85.+p Channeling phenomena (blocking, energy loss, etc.)
61.80.Jh Ion radiation effects
61.72.uf Ge and Si
61.82.Fk Semiconductors

Growth mode transition from layer by layer to step flow during the growth of heteroepitaxial SrRuO3 on (001) SrTiO3

J. Choi, C. B. Eom, G. Rijnders, H. Rogalla, and D. H. A. Blank

Appl. Phys. Lett. 79, 1447 (2001); http://dx.doi.org/10.1063/1.1389837 (3 pages) | Cited 65 times

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We have observed the growth mode transition from two-dimensional (2D) layer-by-layer to step-flow in the earliest stage growth of heteroepitaxial SrRuO3 thin films on TiO2-terminated (001) SrTiO3 substrates by in situ high pressure reflective high energy electron diffraction (RHEED) and atomic-force microscopy. There is no RHEED intensity recovery after each laser pulse in the first oscillation when the growth mode is 2D layer-by-layer. On the other hand, it is getting more pronounced in the second oscillation, and finally reaches a dynamic steady state in which the growth mode is completely changed into the step-flow mode. The origin of the growth mode transition can be attributed to a change in the mobility of adatoms and switching the surface termination layer from the substrate to the film. SrRuO3 thin films with an atomically smooth surface grown by atomic layer control can be used in oxide multilayered heterostructure devices. © 2001 American Institute of Physics.
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68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition
68.43.Mn Adsorption kinetics

Ab initio calculations of the mechanical properties of Ti3SiC2

Bengt Holm, Rajeev Ahuja, and Börje Johansson

Appl. Phys. Lett. 79, 1450 (2001); http://dx.doi.org/10.1063/1.1392981 (3 pages) | Cited 41 times

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We present results of first-principles calculations of the elastic constants and other mechanical properties of Ti3SiC2. This knowledge is important from a technological point of view, since the material shows promising characteristics, such as a combined metallic and ceramic appearance. We also confirm a recent experimental observation that the structure of Ti3SiC2 is stable at elevated pressures, and investigate some consequences of this fact. © 2001 American Institute of Physics.
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62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.66.Fn Inorganic compounds
71.20.Ps Other inorganic compounds

Interstitial oxygen loss and the formation of thermal double donors in Si

Young Joo Lee, J. von Boehm, and R. M. Nieminen

Appl. Phys. Lett. 79, 1453 (2001); http://dx.doi.org/10.1063/1.1389505 (3 pages) | Cited 7 times

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The combination of first-principles total energy calculations and a general kinetic model, which takes into account all processes of association, dissociation, and restructuring, is used to study the kinetics of thermal double donors (TDDs) in silicon over the temperature range of 300–650 °C. A strong correlation is found between the formation rate of TDDs and the loss rate of interstitial oxygen atoms. Also, a close agreement with experiments is obtained. It is found that TDDs grow via consecutive reactions where fast diffusing oxygen dimers and all TDDs capture interstitial oxygen atoms. © 2001 American Institute of Physics.
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61.72.S- Impurities in crystals
71.55.Cn Elemental semiconductors

Processing of carbon-fiber-reinforced Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass composites

C. P. Kim, R. Busch, A. Masuhr, H. Choi-Yim, and W. L. Johnson

Appl. Phys. Lett. 79, 1456 (2001); http://dx.doi.org/10.1063/1.1390317 (3 pages) | Cited 52 times

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Carbon-fiber-reinforced bulk metallic glass composites are produced by infiltrating liquid Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 into carbon fiber bundles with diameter of the individual fiber of 5 μm. Reactive wetting occurs by the formation of a ZrC layer around the fibers. This results in a composite with a homogeneous fiber distribution. The volume fraction of the fibers is about 50% and the density of the composite amounts to 4.0 g/cm3. © 2001 American Institute of Physics.
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81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
81.05.Pj Glass-based composites, vitroceramics

Growth of crack-free hexagonal GaN films on Si(100)

J. Wan, R. Venugopal, M. R. Melloch, H. M. Liaw, and W. J. Rummel

Appl. Phys. Lett. 79, 1459 (2001); http://dx.doi.org/10.1063/1.1400770 (3 pages) | Cited 11 times

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Hexagonal GaN films have been grown on Si(100) substrates by employing a sputtered AlN buffer layer followed by another high-temperature metalorganic chemical vapor deposition (MOCVD) grown AlN buffer layer. The highly oriented structure of sputtered AlN provides a hexagonal template for subsequent AlN and GaN growth. The GaN films are evaluated by transmission electron microscopy, selected area electron diffraction, x-ray diffraction, and photoluminescence and exhibit a purely hexagonal columnar structure. The orientation of the GaN columns depends on the thickness of both the sputtered AlN buffer layer and the MOCVD grown AlN buffer layer. The surface of GaN films is shiny and crack free up to a thickness of 2 μm studied in this work. © 2001 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
61.72.-y Defects and impurities in crystals; microstructure
68.55.-a Thin film structure and morphology
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Metal/III–V diodes engineered by means of Si interlayers: Interface reactions versus local interface dipoles

B. Bonanni, D. Orani, M. Lazzarino, S. Rubini, and A. Franciosi

Appl. Phys. Lett. 79, 1462 (2001); http://dx.doi.org/10.1063/1.1399310 (3 pages)

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We present studies of Al/n-GaAs(001) and Al/p-GaAs(001) diodes in which the Schottky barrier height was varied by fabricating Si bilayers at the interface under either Ga or Al flux. Comparison of the effect of each interlayer on the n- and p-type barrier height allowed us to rule out any major role of interface reactions and test the predictions of the local interface-dipole model of Schottky barrier tuning. © 2001 American Institute of Physics.
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85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes
68.35.Ct Interface structure and roughness
73.20.At Surface states, band structure, electron density of states
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
85.30.De Semiconductor-device characterization, design, and modeling

Coulomb blockade in multiwalled carbon nanotube island with nanotube leads

Nobuhide Yoneya, Eiichirou Watanabe, Kazuhito Tsukagoshi, and Yoshinobu Aoyagi

Appl. Phys. Lett. 79, 1465 (2001); http://dx.doi.org/10.1063/1.1399301 (3 pages) | Cited 14 times

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We propose and demonstrate a technique to form an ultrasmall island for a single-electron transistor in a multiwalled carbon nanotube (MWNT). The two small areas in the MWNT connected to electrodes were etched in oxygen plasma, resulting in the cutting of the MWNT into three pieces. An island and two leads connected the island through the tunneling barriers were made of the MWNT. In this device, we observed the Coulomb blockade effect at 4.5 K, and the estimated charging energy was 38 meV. This result is an essential step for the use of carbon nanotubes in nanoscale electronics circuits. © 2001 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
85.35.Ds Quantum interference devices
85.35.Gv Single electron devices
73.63.Fg Nanotubes

Effect of N/Ge co-implantation on the Ge activation in GaN

Yoshitaka Nakano and Tetsu Kachi

Appl. Phys. Lett. 79, 1468 (2001); http://dx.doi.org/10.1063/1.1400089 (3 pages) | Cited 9 times

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N-type regions have been produced in undoped GaN films by Ge and N/Ge implantation, sequentially, and subsequent annealing with a SiO2 encapsulation layer at 1300 °C. Improved Ge-doping characteristics have been achieved for GaN by N/Ge co-implantation, attaining activation efficiencies above 95%, whereas in the case of conventional Ge implantation, the activation efficiency is low owing to the generation of N vacancies. In particular, overlapping of the N-implanted region with the Ge one can make the Ge activation higher at a N/Ge ratio of ∼1. Therefore, the co-implantation of additional N atoms drastically enhances the Ge activation based on a site-competition effect. © 2001 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters

Efficient electronic cooling in heavily doped silicon by quasiparticle tunneling

A. M. Savin, M. Prunnila, P. P. Kivinen, J. P. Pekola, J. Ahopelto, and A. J. Manninen

Appl. Phys. Lett. 79, 1471 (2001); http://dx.doi.org/10.1063/1.1399313 (3 pages) | Cited 23 times

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Cooling of electrons in a heavily doped silicon by quasiparticle tunneling using a superconductor–semiconductor–superconductor double-Schottky-junction structure is demonstrated at low temperatures. In this work, we use Al as the superconductor and thin silicon-on-insulator (SOI) film as the semiconductor. The electron–phonon coupling is measured for the SOI film and the low value of the coupling is shown to be the origin of the observed significant cooling effect. © 2001 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Gk Tunneling
73.30.+y Surface double layers, Schottky barriers, and work functions
74.50.+r Tunneling phenomena; Josephson effects
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Strain and composition distribution in uncapped SiGe islands from x-ray diffraction

J. Stangl, A. Daniel, V. Holý, T. Roch, G. Bauer, I. Kegel, T. H. Metzger, Th. Wiebach, O. G. Schmidt, and K. Eberl

Appl. Phys. Lett. 79, 1474 (2001); http://dx.doi.org/10.1063/1.1392975 (3 pages) | Cited 36 times

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We have investigated the strain and composition distribution in uncapped SiGe islands grown on Si (001) by x-ray diffraction. In order to be sensitive to the dot layer on the sample surface, and at the same time being able to measure in-plane strain and strain in growth direction, we utilized a scattering geometry at grazing incidence angles, but with high exit angles. The measured intensity distribution is compared to simulations based on the strain distribution calculated by a finite element method. Although pure Ge has been deposited during island growth by molecular beam epitaxy, the Ge composition varies from 0.5 at the island base to 1.0 at the top of the islands. Even at this top, the elastic relaxation reaches only about 50%. © 2001 American Institute of Physics.
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68.55.Nq Composition and phase identification
68.60.Bs Mechanical and acoustical properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Crystal orientation dependence of optical gain in InGaN/GaN multiple-quantum-well structures

Chii-Chang Chen, Kun-Long Hsieh, Jinn-Kong Sheu, Gou-Chung Chi, Ming-Juinn Jou, Chih-Hao Lee, and Ming-Zhe Lin

Appl. Phys. Lett. 79, 1477 (2001); http://dx.doi.org/10.1063/1.1402155 (3 pages) | Cited 5 times

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The net modal gain of the InGaN/GaN multiple quantum well has been measured by the variable excitation stripe length method for an optically pumped cavity along each crystal orientation on the (0001) plane. These results demonstrated the theoretical prediction of the fact that the maximum optical gain can be obtained at a [1210]-oriented edge-emitting laser cavity, which has been reported in the literature. “Crystal orientation” is confirmed to be a related parameter to the optical gain for a GaN-based strained structure. © 2001 American Institute of Physics.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Simultaneously enhanced thermoelectric power and reduced resistivity of NaxCo2O4 by controlling Na nonstoichiometry

T. Motohashi, E. Naujalis, R. Ueda, K. Isawa, M. Karppinen, and H. Yamauchi

Appl. Phys. Lett. 79, 1480 (2001); http://dx.doi.org/10.1063/1.1400777 (3 pages) | Cited 76 times

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Electrical resistivity (ρ) and thermoelectric power (S) were measured for NaxCo2O4 samples with various Na contents (x). A highly precise control of Na nonstoichiometry was facilitated by optimizing the synthesis procedure. With increasing x, the absolute value of ρ monotonically decreased, while the value of S increased. For the x = 1.5 sample, S reached a value as high as ∼ 120 μV/K (at 300 K). © 2001 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
61.66.Bi Elemental solids
61.66.Dk Alloys
72.20.Fr Low-field transport and mobility; piezoresistance

Piezoelectric field and its influence on the pressure behavior of the light emission from GaN/AlGaN strained quantum wells

S. P. Łepkowski, H. Teisseyre, T. Suski, P. Perlin, N. Grandjean, and J. Massies

Appl. Phys. Lett. 79, 1483 (2001); http://dx.doi.org/10.1063/1.1396631 (3 pages) | Cited 25 times

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We have studied the influence of hydrostatic pressure on the light emission from a strained GaN/AlGaN multiquantum well system. We have found that the pressure coefficients of the photoluminescence peak energies are dramatically reduced with respect to that of GaN energy gap and this reduction is a function of the quantum well thickness. The decrease of the light emission pressure coefficient may be as large as 30% for a 32 monolayer (8 nm) thick quantum well. We explain this effect by the hydrostatic-pressure-induced increase of the piezoelectric field in quantum structures. Model calculations based on the k×p method and linear elasticity theory reproduce the experimental results well, demonstrating that this increase may be explained by small anisotropy of the wurtzite lattice of GaN and a specific interplay of elastic constants and values of the piezoelectric tensor. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.67.De Quantum wells
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
73.21.Fg Quantum wells
81.07.St Quantum wells
73.21.Cd Superlattices
77.65.-j Piezoelectricity and electromechanical effects
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
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