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26 Jan 2004

Volume 84, Issue 4, pp. 457-639

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 625 (2004); http://dx.doi.org/10.1063/1.1644326 (3 pages)

A. M. Clark, A. Williams, S. T. Ruggiero, M. L. van den Berg, and J. N. Ullom
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Efficiency enhancement in a light-emitting diode with a two-dimensional surface grating photonic crystal

Hiroyuki Ichikawa and Toshihiko Baba

Appl. Phys. Lett. 84, 457 (2004); http://dx.doi.org/10.1063/1.1644033 (3 pages) | Cited 63 times

Online Publication Date: 21 January 2004

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We demonstrate a light-emitting diode exhibiting 1.7–2.7-fold enhancement in light extraction efficiency compared with that for a planer device. It has a two-dimensional surface grating photonic crystal, which diffracts internal light with a large solid angle into the escape light cone. Due to its shallow grating separated from the active layer and micron order lattice constant, the fabrication process is simple, applicable to arbitrary semiconductor devices, and free from process-induced nonradiative recombinations. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Qs Photonic bandgap materials

Two-dimensional photonic crystal Mach–Zehnder interferometers

M. H. Shih, W. J. Kim, Wan Kuang, J. R. Cao, H. Yukawa, S. J. Choi, J. D. O’Brien, P. D. Dapkus, and W. K. Marshall

Appl. Phys. Lett. 84, 460 (2004); http://dx.doi.org/10.1063/1.1642758 (3 pages) | Cited 31 times

Online Publication Date: 21 January 2004

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Mach–Zehnder interferometers were fabricated from suspended membrane photonic crystal waveguides. Transmission spectra were measured and device operation was shown to be in agreement with theoretical predictions. © 2004 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
07.60.Ly Interferometers
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states

Optically pumped ultraviolet AlGaInN quantum well laser at 340 nm wavelength

Y. He, Y.-K. Song, A. V. Nurmikko, J. Su, M. Gherasimova, G. Cui, and J. Han

Appl. Phys. Lett. 84, 463 (2004); http://dx.doi.org/10.1063/1.1637960 (3 pages) | Cited 1 time

Online Publication Date: 21 January 2004

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We have demonstrated and characterized an optically pumped room temperature pulsed laser at 340 nm, based on a separate confinement AlGaInN multiple quantum well heterostructure design. The lasing was achieved at threshold peak power of ∼ 800 kW/cm2. Gain spectroscopy showed modest peak modal gain on the order of 5 cm−1, suggesting that the combination of weak optical confinement and nonradiative recombination would lead to high threshold currents for comparably constructed diode lasers. © 2004 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.)

III-nitride blue and ultraviolet photonic crystal light emitting diodes

T. N. Oder, K. H. Kim, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 84, 466 (2004); http://dx.doi.org/10.1063/1.1644050 (3 pages) | Cited 143 times

Online Publication Date: 21 January 2004

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We present results on enhancement of 460 nm blue and 340 nm UV optical power output in III-nitride light emitting diodes (LEDs) using photonic crystals (PCs) under current injection. Triangular arrays of the PCs with diameter/periodicity of 300/700 nm were patterned using electron-beam lithography and inductively coupled plasma dry etching. The total power at 20 mA of 300×300 μm2 unpackaged LED chips revealed an increase by 63% and 95% for the blue and UV LEDs, respectively, as a result of the PC formation. Possible ways for further improving enhancement of light extraction using PCs are discussed. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Qs Photonic bandgap materials

Optically controlled electroabsorption modulators for unconstrained wavelength conversion

V. A. Sabnis, H. V. Demir, O. Fidaner, J. S. Harris, D. A. B. Miller, J.-F. Zheng, N. Li, T.-C. Wu, H.-T. Chen, and Y.-M. Houng

Appl. Phys. Lett. 84, 469 (2004); http://dx.doi.org/10.1063/1.1643539 (3 pages) | Cited 14 times

Online Publication Date: 21 January 2004

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We introduce a proof-of-concept, optically controlled, optical switch based on the monolithic integration of a surface-illuminated photodetector and a waveguide electroabsorption modulator. We demonstrate unconstrained wavelength conversion over the entire center telecommunication wavelength band (C band) and optical switching up to 2.5 Gbit/s with extinction ratios exceeding 10 dB. Our approach offers both high-speed, low-power, switching operation and two-dimensional array scalability for the fabrication of chip-scale reconfigurable multichannel wavelength converters. © 2004 American Institute of Physics.
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42.79.Nv Optical frequency converters
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.65.Pc Optical bistability, multistability, and switching, including local field effects
85.60.Gz Photodetectors (including infrared and CCD detectors)

Towards ultranarrow bandwidth polymer-based resonant grating waveguide structures

T. Katchalski, E. Teitelbaum, and A. A. Friesem

Appl. Phys. Lett. 84, 472 (2004); http://dx.doi.org/10.1063/1.1644330 (3 pages) | Cited 5 times

Online Publication Date: 21 January 2004

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The needed parameters and configurations that would lead to the achievement of ultranarrow spectral bandwidths in polymer-based resonant grating waveguide structures are presented. These include the addition of an upper polymeric layer to the basic configuration and increasing the waveguide thickness. The results reveal that spectral bandwidths as narrow as 0.15 nm at 1.5 μm can be achieved. © 2004 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.79.Dj Gratings
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.70.Jk Polymers and organics

Terahertz range quantum well infrared photodetector

Marcel Graf, Giacomo Scalari, Daniel Hofstetter, Jérôme Faist, Harvey Beere, Edmund Linfield, David Ritchie, and Giles Davies

Appl. Phys. Lett. 84, 475 (2004); http://dx.doi.org/10.1063/1.1641165 (3 pages) | Cited 66 times

Online Publication Date: 21 January 2004

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We demonstrated a GaAs/AlGaAs-based far-infrared quantum well infrared photodetector at a wavelength of λ=84 μm. The relevant intersubband transition is slightly diagonal with a dipole matrix element of 3.0 nm. At 10 K, a responsivity of 8.6 mA/W and a detectivity of 5×107 cm √Hz/W have been achieved; and successful detection up to a device temperature of 50 K has been observed. Being designed for zero bias operation, this device profits from a relatively low dark current and a good noise behavior. © 2004 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Pw Imaging detectors and sensors
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Annealing effects on optical and structural properties of 1.3-μm GaInNAs/GaAs quantum-well samples capped with dielectric layers

H. F. Liu, C. S. Peng, E.-M. Pavelescu, T. Jouhti, S. Karirinne, J. Konttinen, and M. Pessa

Appl. Phys. Lett. 84, 478 (2004); http://dx.doi.org/10.1063/1.1644028 (3 pages) | Cited 12 times

Online Publication Date: 21 January 2004

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Effects of thermal annealing on photoluminescence (PL) and x-ray diffraction from metastable GaInNAs/GaAs quantum-well samples covered by dielectric layers have been studied. PL from uncoated samples exhibits a saturable blueshift of 22 meV relative to PL from the as-grown samples in these experiments. The shift is attributable to a change in the nearest neighbors of nitrogen in short-range-order N-InmGa4−m (0 ⩽ m ⩽ 4) clusters at a fixed composition with negligible Ga/In/N interdiffusion. A Si3N4 cap layer effectively prevents the blueshift in the early stage of annealing and improves emission intensity. Under severe annealing conditions (750 °C for 1500 s), the maximum blueshift for the Si3N4-covered samples is 31 meV. A SiO2 cap layer causes a large nonsaturable blueshift, almost 100 meV in these experiments. The large blueshift is assigned to the formation of defects (likely Ga vacancies) at the SiO2/GaAs interface. The defects are believed to diffuse into the bulk at elevated temperatures and to assist Ga/In/N interdiffusion. © 2004 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.65.Fg Quantum wells
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.67.De Quantum wells

Local structure around Mn atoms in room-temperature ferromagnetic (In,Mn)As thin films probed by extended x-ray absorption fine structure

Y. L. Soo, S. Kim, Y. H. Kao, A. J. Blattner, B. W. Wessels, S. Khalid, C. Sanchez Hanke, and C.-C. Kao

Appl. Phys. Lett. 84, 481 (2004); http://dx.doi.org/10.1063/1.1640465 (3 pages) | Cited 29 times

Online Publication Date: 21 January 2004

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An extended x-ray absorption fine structure technique has been employed to probe the average local structure around Mn impurity atoms in (In,Mn)As thin films prepared by organometallic vapor phase epitaxy. These films show ferromagnetism above room temperature. As the concentration of Mn increases, the average local environment surrounding Mn changes from that of a Mn–Mn interstitial pair to a dimer, trimer, or cubic MnAs structure and then to the hexagonal MnAs structure/interstitial pair. In contrast to random substitution, the Mn impurity atoms in these dimer, trimer, or cubic MnAs structure occupy adjacent sites in the In sublattice. Ferromagnetism above room temperature in these ordered substitutional samples provides an excellent example for ferromagnetic exchange interaction in (In,Mn)As diluted magnetic semiconductors without the formation of hexagonal MnAs clusters, this is potentially very important for spintronic applications. © 2004 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.70.Dm X-ray absorption spectra
61.72.S- Impurities in crystals
75.50.Pp Magnetic semiconductors

Reduction of threading dislocations in GaN layers using in situ deposited silicon nitride masks on AlN and GaN nucleation layers

X. L. Fang, Y. Q. Wang, H. Meidia, and S. Mahajan

Appl. Phys. Lett. 84, 484 (2004); http://dx.doi.org/10.1063/1.1642274 (3 pages) | Cited 19 times

Online Publication Date: 21 January 2004

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We have examined the influence of thin layers of silicon nitride, deposited in situ on AlN and GaN nucleation layers (NLs), on the density of threading dislocations (TDs) in GaN overgrowths. Results indicate that TD density is reduced to 2–4×108 cm−2. In GaN/silicon nitride/AlN–NL/sapphire composites, alternating regions of low and high TD density coexist in the overgrowth, and microstructural features characteristic of epitaxial lateral overgrowth techniques are seen. On the other hand, such features are absent in GaN/silicon nitride/GaN–NL/sapphire composites, and TDs are uniformly distributed. © 2004 American Institute of Physics.
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85.40.Sz Deposition technology
85.30.-z Semiconductor devices
85.40.Hp Lithography, masks and pattern transfer

Viscous flow of the Pd43Ni10Cu27P20 bulk metallic glass-forming liquid

G. J. Fan, H.-J. Fecht, and E. J. Lavernia

Appl. Phys. Lett. 84, 487 (2004); http://dx.doi.org/10.1063/1.1644052 (3 pages) | Cited 41 times

Online Publication Date: 21 January 2004

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The equilibrium viscosity of the Pd43Ni10Cu27P20 bulk metallic glass-forming liquid was measured over a wide temperature range from the equilibrium supercooled liquid state to the glass transition region using parallel-plate rheometry and three-point beam bending. Based on the measured viscosity data, the fragility of this liquid was quantitatively determined. The Pd43Ni10Cu27P20 alloy, despite exhibiting the best glass-forming ability reported thus far, is relatively fragile compared with other bulk glass-forming liquids, such as Vit 1 and Vit 4. © 2004 American Institute of Physics.
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66.20.-d Viscosity of liquids; diffusive momentum transport
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses

Determination of In concentration in pseudomorphic InxGa1−xN quantum wells based on convergent-beam electron diffraction

J. N. Stirman, M. Takeguchi, M. R. McCartney, and David J. Smith

Appl. Phys. Lett. 84, 490 (2004); http://dx.doi.org/10.1063/1.1641173 (3 pages) | Cited 2 times

Online Publication Date: 21 January 2004

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An approach based on the technique of convergent-beam electron diffraction (CBED) has been used to determine the elemental composition of a pseudomorphic GaN/InxGa1−xN/GaN quantum-well structure on the nanometer scale. Areas of triangles formed by intersecting higher order Laue-zone (HOLZ) lines are highly sensitive to lattice-parameter variations. By calculating the ratio of triangle areas, the local In concentration is estimated to within ±0.5% once lattice expansion in the growth direction has been taken into account. Moreover, shifts in the HOLZ-line positions as the CBED probe is moved along the quantum well provide a simple and rapid indication of local fluctuations in In content. The technique is applicable to other pseudomorphically strained epitaxial layers. © 2004 American Institute of Physics.
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68.65.Fg Quantum wells
61.05.jm Convergent-beam electron diffraction, selected-area electron diffraction, nanodiffraction

Infrared spectroscopic analysis of an ordered Si/SiO2 interface

K. T. Queeney, N. Herbots, Justin M. Shaw, V. Atluri, and Y. J. Chabal

Appl. Phys. Lett. 84, 493 (2004); http://dx.doi.org/10.1063/1.1644030 (3 pages) | Cited 10 times

Online Publication Date: 21 January 2004

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Infrared spectroscopy is used to compare the Si/SiO2 interfaces created by thermal oxidation of a standard Si(100) substrate and of an ordered, (1×1) Si(100) substrate. The thermal oxides (approximately 25 Å) examined in this study are etched in dilute hydrofluoric acid and the resulting films analyzed spectroscopically. The behavior of the dominant optical phonon modes as a function of film thickness provides strong evidence that the ordered Si(100) substrate provides a template for an Si/SiO2 interface with a higher degree of homogeneity in the Si–O bonding environment of the intervening substoichiometric SiOx layer than does the standard Si(100) substrate. © 2004 American Institute of Physics.
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68.47.Fg Semiconductor surfaces
78.30.Am Elemental semiconductors and insulators
81.65.Mq Oxidation
78.66.Nk Insulators

Well-width dependence of photoluminescence emission from a-plane GaN/AlGaN multiple quantum wells

M. D. Craven, P. Waltereit, J. S. Speck, and S. P. DenBaars

Appl. Phys. Lett. 84, 496 (2004); http://dx.doi.org/10.1063/1.1638884 (3 pages) | Cited 58 times

Online Publication Date: 21 January 2004

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This work investigates the room-temperature photoluminescence (PL) characteristics of nonpolar GaN/( ∼ 100 Å Al0.16Ga0.84N) multiple quantum wells (MQWs) in comparison to c-plane structures as a function of GaN quantum well width. 10-period a-plane and c-plane MQW structures were simultaneously regrown on the appropriate GaN/sapphire template layers via metalorganic chemical vapor deposition with well widths ranging from 20 to 70 Å. The PL emission energy from a-plane MQWs followed a square well trend modeled using self-consistent Poisson–Schrödinger calculations while the c-plane MQW emission showed a significant redshift with increasing well width which is attributed to the quantum-confined Stark effect. Despite a higher dislocation density, the a-plane MQWs exhibit enhanced recombination efficiency as compared to the c-plane wells since well emission is no longer observed for c-plane wells wider than 50 Å. Optimal PL emission intensity was obtained for 52 Å a-plane wells compared to 28 Å c-plane wells, revealing the effects of internal fields on quantum well emission. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.20.Jq Electro-optical effects

Anisotropic structural characteristics of (11math0) GaN templates and coalesced epitaxial lateral overgrown films deposited on (10math2) sapphire

Hongmei Wang, Changqing Chen, Zheng Gong, Jianping Zhang, Mikhail Gaevski, Ming Su, Jinwei Yang, and M. Asif Khan

Appl. Phys. Lett. 84, 499 (2004); http://dx.doi.org/10.1063/1.1644054 (3 pages) | Cited 69 times

Online Publication Date: 21 January 2004

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a-plane GaN templates and coalesced epitaxial lateral overgrown (ELOG) films on r-plane sapphire substrates were investigated by x-ray diffraction (XRD). The a-plane GaN templates were found to have [0001]-oriented stripe-features, which is related to anisotropic mosaicity. For the mosaic blocks, the mosaicity reached the largest and the smallest values along the [1math00] and the [0001] directions. The ELOG procedure with the SiO2 mask stripes perpendicular to the [0001] direction limits the preferable growth along this direction, and thereby enhances the [1100] growth. This leads to large-area, featureless, a-plane GaN films for which the wing tilt and not the fine mosaic block size becomes the major XRD line-broadening mechanism. © 2004 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors
85.40.Hp Lithography, masks and pattern transfer

V defects of ZnO thin films grown on Si as an ultraviolet optical path

Y.-Z. Yoo, T. Sekiguchi, T. Chikyow, M. Kawasaki, T. Onuma, S. F. Chichibu, J. H. Song, and H. Koinuma

Appl. Phys. Lett. 84, 502 (2004); http://dx.doi.org/10.1063/1.1643535 (3 pages) | Cited 16 times

Online Publication Date: 21 January 2004

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V defects were observed in the ZnO films epitaxially grown on the ZnS-buffered Si. Although the defects were located on the surface, strong near-bandedge emission confined to the {10math1} facets of V defects was observed at room temperature. The near-bandedge emission spreads out over the whole film centering at V defects at 30 K. The detailed optical characterization shows that activation of excitonic absorption is responsible for this unique optical behavior. © 2004 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
71.55.Gs II-VI semiconductors
68.37.Ps Atomic force microscopy (AFM)
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.J- Point defects and defect clusters

Enhanced surface diffusion through termination conversion during epitaxial SrRuO3 growth

Guus Rijnders, Dave H. A. Blank, Junghoon Choi, and Chang-Beom Eom

Appl. Phys. Lett. 84, 505 (2004); http://dx.doi.org/10.1063/1.1640472 (3 pages) | Cited 47 times

Online Publication Date: 21 January 2004

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During the initial growth of the ferromagnetic oxide SrRuO3 on TiO2-terminated SrTiO3, we observe a self-organized conversion of the terminating atomic layer from RuO2 to SrO. This conversion induces an abrupt change in growth mode from layer by layer to growth by step advancement, indicating a large enhancement of the surface diffusivity. This growth mode enables the growth of single-crystalline and single-domain thin films. Both conversion and the resulting growth mode enable the control of the interface properties in heteroepitaxial multilayer structures on an atomic level. © 2004 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.35.Fx Diffusion; interface formation

Elastic and electronic properties of select M2AX phases

S. E. Lofland, J. D. Hettinger, K. Harrell, P. Finkel, S. Gupta, M. W. Barsoum, and G. Hug

Appl. Phys. Lett. 84, 508 (2004); http://dx.doi.org/10.1063/1.1641177 (3 pages) | Cited 69 times

Online Publication Date: 21 January 2004

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In this letter we report on the low-temperature specific heat of several M2AX phases: Ti2AlC, V2AlC, V2AsC, Nb2SnC, Ti2AlN, Hf2InC, Nb2AlC, and Cr2AlC. The Debye temperatures are quite high. The density of states at the Fermi level, N(EF) varies from ≈1.4 (eV formula unit)−1 to 6 (eV formula unit)−1. Ab initio calculations show that N(EF) is dictated by the transition metal d–d bands; the A-group element has little effect. We also measured the velocity of sound in V2AlC, V2AsC, Ti2AlC, and Ti2AlN. The average bulk modulus of these materials is over 100 GPa, with a high of ≈140 GPa for Ti2AlN. Our theoretical calculations correctly predict the trend in both the density of states and the bulk modulus, although there is some disagreement in the actual values. © 2004 American Institute of Physics.
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65.40.Ba Heat capacity
71.20.Be Transition metals and alloys
62.20.D- Elasticity

Quantum dot/substrate interaction in InAs/In0.53Ga0.47As/InP(001)

X. Z. Liao, Y. T. Zhu, Y. M. Qiu, D. Uhl, and H. F. Xu

Appl. Phys. Lett. 84, 511 (2004); http://dx.doi.org/10.1063/1.1642754 (3 pages) | Cited 1 time

Online Publication Date: 21 January 2004

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InAs quantum dots grown on In0.53Ga0.47As/InP(001) substrate by low-pressure metalorganic chemical vapor deposition were investigated using high-angle annular dark-field imaging. Results suggest significant mass transport of mainly the large-sized component (InAs) from the In0.53Ga0.47As substrate to InAs quantum dots, an unexpected process that increases the system strain energy. The amount of the transported mass increases with quantum dot size. Two monolayers of GaAs inserted between InAs islands and the InGaAs substrate appears to block or at least effectively slow down this mass transport process. © 2004 American Institute of Physics.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.Hb Quantum dots (patterned in quantum wells)

Glass transition-assisted microstructuring in polystyrene

Saulius Juodkazis, Kazuhiko Yamasaki, Shigeki Matsuo, and Hiroaki Misawa

Appl. Phys. Lett. 84, 514 (2004); http://dx.doi.org/10.1063/1.1641182 (3 pages) | Cited 9 times

Online Publication Date: 21 January 2004

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We report on the use of a shape transition process to resize patterns prerecorded inside polystyrene film. The shape transition, which is shrinkage in two dimensions and expansion in the third (the volume is conserved), was brought about by annealing polystyrene above the glass transition temperature. This caused approximately twofold lateral shrinkage and fourfold axial stretching of the film, inside which micrometer-sized patterns had been recorded by femtosecond pulses. The transformation of these patterns corresponded to the macroscopic shape transformation of the film. The shape transition was also used to transform a diffraction grating. This allowed the transformation to be confirmed by the corresponding change in diffraction efficiency. The applicability of the shape transition process to nanofabrication is discussed. © 2004 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.41.+e Polymers, elastomers, and plastics

Impact of current crowding on electromigration-induced mass transport

H. Wang, C. Bruynseraede, and K. Maex

Appl. Phys. Lett. 84, 517 (2004); http://dx.doi.org/10.1063/1.1644048 (3 pages) | Cited 10 times

Online Publication Date: 21 January 2004

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To assess the relevance of current crowding to electromigration-induced mass transport, a test structure was designed to structurally induce and accelerate current crowding in Cu damascene lines. Electromigration experiments and quantitative finite element analysis demonstrate how current crowding can substantially enhance local atomic flux along critical diffusion paths. The resulting flux divergence leads to rapid void nucleation and growth. The observed increase in atomic flux and flux divergence is also moderately affected by the presence of Joule-heating-induced temperature gradients. © 2004 American Institute of Physics.
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66.30.Qa Electromigration
02.70.Dh Finite-element and Galerkin methods
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Qq Microscopic defects (voids, inclusions, etc.)
66.30.Dn Theory of diffusion and ionic conduction in solids

Low-glancing-angle x-ray diffraction study on the relationship between crystallinity and properties of C60 field effect transistor

Hirotaka Ohashi, Katsumi Tanigaki, Ryotaro Kumashiro, Syuji Sugihara, Shinya Hiroshiba, Shigeru Kimura, Kenichi Kato, and Masaki Takata

Appl. Phys. Lett. 84, 520 (2004); http://dx.doi.org/10.1063/1.1638882 (3 pages) | Cited 8 times

Online Publication Date: 21 January 2004

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The structures of C60 thin films grown on Si, SiO2, and Al2O3 are studied by a low-glancing-angle x-ray diffraction method and the properties of C60 field effect transistors (FETs) are understood on a basis of this technique. Analyses using the two-dimensional Ewald circle and the Laue function give the detailed interpretation of the diffraction peaks together with information of the preferred orientation and the grain size of polycrystalline thin films. The grain size varies from 100 to 500 Å upon the optimal conditions of the thin film growth and the preferred orientation of the C60 〈111〉 crystal axis with random on a substrate surface is obtained. It is clearly shown that these variations in quality of the C60 thin films exert unexpectedly little influence on the FET characteristics. © 2004 American Institute of Physics.
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61.05.cm X-ray reflectometry (surfaces, interfaces, films)
81.05.ub Fullerenes and related materials
85.30.Tv Field effect devices

The Urbach focus and hydrogenated amorphous silicon

Farida Orapunt and Stephen K. O’Leary

Appl. Phys. Lett. 84, 523 (2004); http://dx.doi.org/10.1063/1.1641176 (3 pages) | Cited 6 times

Online Publication Date: 21 January 2004

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We critically examine the validity of the Urbach “focus” concept for the case of hydrogenated amorphous silicon. Our approach involves an analysis of a broad assortment of hydrogenated amorphous silicon experimental optical absorption data from many different sources. We find that these experimental data are consistent with the notion of the Urbach focus concept. The implications of this conclusion are explored. © 2004 American Institute of Physics.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses

Positional disorder of oxygen ions in ceria at high temperatures

Masatomo Yashima and Syuuhei Kobayashi

Appl. Phys. Lett. 84, 526 (2004); http://dx.doi.org/10.1063/1.1644053 (3 pages) | Cited 12 times

Online Publication Date: 21 January 2004

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Accurate nuclear density distribution of ceria, CeO2 has been studied between 1005 and 1497 °C by the maximum-entropy method-based pattern fitting combined with the Rietveld method using neutron powder diffraction data. The results reveal that the oxygen ions have a complicated disorder spreading over a wide area and shift to the 〈111〉 directions from the ideal fluorite position. This feature is more significant at higher temperatures, which is consistent with the higher ionic conductivity. © 2004 American Institute of Physics.
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61.43.Gt Powders, porous materials
66.30.H- Self-diffusion and ionic conduction in nonmetals
83.85.Hf X-ray and neutron scattering
61.66.Fn Inorganic compounds

The effect of mixed Mn valences on Li migration in LiMn2O4 spinel: A molecular dynamics study

Kenji Tateishi, Douglas du Boulay, and Nobuo Ishizawa

Appl. Phys. Lett. 84, 529 (2004); http://dx.doi.org/10.1063/1.1644320 (3 pages) | Cited 4 times

Online Publication Date: 21 January 2004

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Previous molecular dynamics (MD) simulations have shown that, with good choice of potential shapes and parameters, the structure and properties of stoichiometric LiMn2O4 can be reproduced to good accuracy. In particular, the experimentally observed self-diffusion of Li ions was shown to occur only for a discrete, mixed Mn valence model. Here, those MD studies have been extended, demonstrating that periodically switching the Mn valence states, reflecting an electron hopping model, greatly facilitates the Li ion self-diffusion. The interaction is mediated by the O atoms, which coordinate both cations and temporarily adopt local distortions based on the three coordinating Mn valences. Although the O atoms continue to vibrate harmonically about a displaced mean, permitting the Li atoms to migrate, the time and spatial average remains that of the ideal spinel with distributed Li. © 2004 American Institute of Physics.
Show PACS
71.28.+d Narrow-band systems; intermediate-valence solids
66.30.H- Self-diffusion and ionic conduction in nonmetals
68.35.Ja Surface and interface dynamics and vibrations
66.30.Dn Theory of diffusion and ionic conduction in solids
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