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7 Apr 2003

Volume 82, Issue 14, pp. 2197-2358

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 2329 (2003); http://dx.doi.org/10.1063/1.1565509 (3 pages)

D. Fujita and T. Kumakura
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Supercontinuum generation in a highly birefringent microstructured fiber

M. Lehtonen, G. Genty, H. Ludvigsen, and M. Kaivola

Appl. Phys. Lett. 82, 2197 (2003); http://dx.doi.org/10.1063/1.1565679 (3 pages) | Cited 42 times

Online Publication Date: 2 April 2003

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We present experimental results on supercontinuum generation in a highly birefringent microstructured fiber. We show that such a fiber offers clear advantages for continuum generation over weakly birefringent fibers. In particular, the polarization is preserved along the fiber for all the spectral components. Furthermore, the two eigenpolarizations exhibit different dispersion characteristics, which provide a convenient way of tuning the properties of the generated continuum. We investigate the impact of the pump wavelength and pulse duration on the continuum and use the results to generate an ultrabroadband continuum extending from 400 to 1750 nm. © 2003 American Institute of Physics.
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42.81.Gs Birefringence, polarization
42.81.Dp Propagation, scattering, and losses; solitons
42.65.-k Nonlinear optics

Accelerated pre-oxidation method for healing progressive electrical short in organic light-emitting devices

Youngkyoo Kim, Dongkwon Choi, Hyuntaek Lim, and Chang-Sik Ha

Appl. Phys. Lett. 82, 2200 (2003); http://dx.doi.org/10.1063/1.1564872 (3 pages) | Cited 21 times

Online Publication Date: 2 April 2003

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The accelerated pre-oxidation method (APOM) was applied to heal progressive electrical short (PES) in organic light-emitting devices. The APOM applied to the devices showed approximately 100 times lower leakage current and 25% improvement in device efficiency compared to a normal device without the APOM applied. The mean projected lifetime of the APOM devices was more than 2400 h at initial luminance of 100 cd/m2 and 90 °C, whereas the normal device turned off after 15 h of operation at the same temperature due to the PES phenomenon. The best stability at elevated temperature was achieved by using the APOM for the cathode layer. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices

Organic surface emitting laser based on a deep-ultraviolet photopolymer containing thiocyanate groups

Gerald Kranzelbinder, Eric Toussaere, Joseph Zyss, Thomas Kavc, Gregor Langer, and Wolfgang Kern

Appl. Phys. Lett. 82, 2203 (2003); http://dx.doi.org/10.1063/1.1559952 (3 pages) | Cited 11 times

Online Publication Date: 2 April 2003

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Gratings for laser applications are being optically recorded in poly(styrene-co-4-vinylbenzyl thiocyanate) (PST-co-VBT) by deep-ultraviolet lithography (λ<300 nm). The gratings writing configuration is based on interference patterning of this holographic material. Grating structures can be further stabilized and modified by selective amine reaction from the gas phase. Gratings based on refractive index contrast (Δn ∼ +0.02) and on thickness modulation (Δd up to 70 nm) are obtainable from this photoreactive polymer. Holographically recorded structures in films of PST-co-VBT doped with a laser dye are designed for second order distributed feedback operation resulting in low threshold organic laser devices (wL,th = 0.25 μJ cm−2) with laser emission output (TE-mode: λL = 632 nm) directed perpendicular to the film plane. © 2003 American Institute of Physics.
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42.70.Hj Laser materials
42.55.Rz Doped-insulator lasers and other solid state lasers
42.40.Eq Holographic optical elements; holographic gratings
42.70.Jk Polymers and organics
42.60.By Design of specific laser systems
42.55.Mv Dye lasers

Single photon emission from individual GaAs quantum dots

J. Hours, S. Varoutsis, M. Gallart, J. Bloch, I. Robert-Philip, A. Cavanna, I. Abram, F. Laruelle, and J. M. Gérard

Appl. Phys. Lett. 82, 2206 (2003); http://dx.doi.org/10.1063/1.1563050 (3 pages) | Cited 30 times

Online Publication Date: 2 April 2003

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We report on photon correlation measurements on a single quantum dot formed at fluctuations of the interface of a GaAs/GaAlAs quantum well. We demonstrate that under pulsed nonresonant excitation, the quantum dot emits a single photon per pulse. This shows that after the photon emission, there is no refill of the quantum dot by the nearby two-dimensional reservoir of delocalized states. The possibility of delivering Fourier transform limited single photons makes this system a good candidate for exciton- and photon-based quantum information processing schemes. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
73.21.La Quantum dots
78.55.Cr III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Highly efficient molecular organic light-emitting diodes based on exciplex emission

L. C. Palilis, A. J. Mäkinen, M. Uchida, and Z. H. Kafafi

Appl. Phys. Lett. 82, 2209 (2003); http://dx.doi.org/10.1063/1.1563838 (3 pages) | Cited 54 times

Online Publication Date: 2 April 2003

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Highly efficient exciplex emission is observed from molecular organic light-emitting diodes (MOLEDs) based on silole derivatives as emissive and electron transport materials, and a hole transporting amine derivative. A silole derivative, 2,5-di-(3-biphenyl)-1,1-dimethyl- 3,4-diphenylsilacyclopentadiene (PPSPP), which shows blue fluorescence (476 nm) with a high solid-state photoluminescence quantum yield of 85% was used as the emitter. Another silole derivative, 2,5-bis-(2′,2″-bipyridin-6-yl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene which exhibits high electron mobility, was used as the electron transport material. MOLEDs using these two siloles and N,N′-diphenyl-N,N′-(2-napthyl)-(1,1′-phenyl)-4,4′-diamine (NPB) as the hole transporter show electroluminescence (EL) emission centered at 495 nm. This red-shifted EL band relative to the blue fluorescence of PPSPP is assigned to a NPB:PPSPP exciplex. An operating voltage of 4.5 V was measured at 100 cd/m2 and an EL quantum efficiency of 3.4% was achieved at 100 A/m2. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds

Three-dimensional photonic crystals fabricated by visible light holographic lithography

X. Wang, J. F. Xu, H. M. Su, Z. H. Zeng, Y. L. Chen, H. Z. Wang, Y. K. Pang, and W. Y. Tam

Appl. Phys. Lett. 82, 2212 (2003); http://dx.doi.org/10.1063/1.1565682 (3 pages) | Cited 52 times

Online Publication Date: 2 April 2003

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In this report, we present three-dimensional photonic crystals fabricated by a four-beam holographic lithography method using visible photoinduced polymerization. High-quality face-centered-cubic single crystals with a large range of polymeric matrix volume fraction were fabricated using optimal conditions obtained from computer simulations. Optical measurements of the crystals showing photonic band-gap-like behavior are presented for different polymeric matrix volume fractions. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.70.Jk Polymers and organics
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.40.My Applications
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Spatial filtering using media with indefinite permittivity and permeability tensors

D. Schurig and D. R. Smith

Appl. Phys. Lett. 82, 2215 (2003); http://dx.doi.org/10.1063/1.1562344 (3 pages) | Cited 28 times

Online Publication Date: 2 April 2003

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Bilayers of media for which the permittivity and permeability tensors are indefinite—that is, not all principle elements possess the same sign—can be used to construct low-, high-, and bandpass spatial filters. These filters possess sharp adjustable roll-offs, and can operate both below and above free-space cutoff to select specific spatial variation components or beam angles from a source or image. © 2003 American Institute of Physics.
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42.79.Ci Filters, zone plates, and polarizers

Efficient red electroluminescence from organic devices using dye-doped rare earth complexes

Z. R. Hong, C. S. Lee, S. T. Lee, W. L. Li, and S. Y. Liu

Appl. Phys. Lett. 82, 2218 (2003); http://dx.doi.org/10.1063/1.1564631 (3 pages) | Cited 18 times

Online Publication Date: 2 April 2003

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Using rare earth complexes with electron-transporting properties as host materials, and 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as a dopant, bilayer doped electroluminescent (EL) devices with efficient red light emission were fabricated. When a europium complex was adopted, the EL spectrum consisted of emissions from DCJTB and Eu3+ ions. At optimal dopant concentration, an EL efficiency of 5.7 cd/A at 0.04 mA/cm2 was observed. Although the EL efficiency decreased with an increase in current density, it remained higher than 2.0 cd/A with brightness of 347.0 cd/m2 at 5.7 V bias. DCJTB and Eu3+ ions collected the energy of singlet and triplet excitons, respectively, and then gave rise to pure red color emission, suggesting a promising way by which to utilize both singlet and triplet excited states in EL devices. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)

Optical cavity effects in InGaN/GaN quantum-well-heterostructure flip-chip light-emitting diodes

Y. C. Shen, J. J. Wierer, M. R. Krames, M. J. Ludowise, M. S. Misra, F. Ahmed, A. Y. Kim, G. O. Mueller, J. C. Bhat, S. A. Stockman, and P. S. Martin

Appl. Phys. Lett. 82, 2221 (2003); http://dx.doi.org/10.1063/1.1566098 (3 pages) | Cited 56 times

Online Publication Date: 2 April 2003

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Optical cavity effects have a significant influence on the extraction efficiency of InGaN/GaN quantum-well-heterostructure flip-chip light-emitting diodes (FCLEDs). Light emitted from the quantum well (QW) self-interferes due to reflection from a closely placed reflective metallic mirror. The interference patterns couple into the escape cone for light extraction from the FCLED. This effect causes significant changes in the extraction efficiency as the distance between the QW and the metallic mirror varies. In addition, the radiative lifetime of the QW also changes as a function of the distance between the QW and the mirror surface. Experimental results from packaged FCLEDs, supported by optical modeling, show that a QW placed at an optimum distance from the mirror provides a ∼ 2.3× increase in total light output as compared to a QW placed at a neighboring position corresponding to a minimum in overall light extraction. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
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Green, blue, and yellow cathodoluminescence of Ba2B5O9Cl thin-films doped with Tb3+, Tm3+, and Mn2+

Jianhua Hao, J. Gao, and Michael Cocivera

Appl. Phys. Lett. 82, 2224 (2003); http://dx.doi.org/10.1063/1.1565704 (3 pages) | Cited 23 times

Online Publication Date: 2 April 2003

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Green, blue, and yellow cathodoluminescence (CL) have been obtained for thin-films of Ba2B5O9Cl doped with Tb3+, Tm3+, and Mn2+, respectively. These phosphor films were deposited by spray pyrolysis, and then activated in air at temperatures suitable for use on glass substrates. The CL characteristic peaks of the films correspond to transitions between electronic energy levels of Tm3+, Tb3+, and Mn2+ ions. The chromaticity coordinates, dominant wavelength, and color purity were determined for each phosphor. Saturation effects were observed as the beam current density increased. The more severe current saturation of Mn-doped film may be due to a greater ground state deplection of Mn luminescent centers than that of the Tb and Tm. © 2003 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Rs Spray coating techniques
78.66.Nk Insulators
71.55.Ht Other nonmetals

Single quantum dot spectroscopy of CdSe/ZnSe grown on vicinal GaAs substrates

T. Makino, R. André, J.-M. Gérard, R. Romestain, Le Si Dang, M. Bartels, K. Lischka, and D. Schikora

Appl. Phys. Lett. 82, 2227 (2003); http://dx.doi.org/10.1063/1.1565700 (3 pages) | Cited 4 times

Online Publication Date: 2 April 2003

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We investigated the optical properties of two monolayers of CdSe sandwiched by ZnSe layers grown by molecular-beam epitaxy on GaAs substrates with a vicinal tilt of 2° in the [111] direction. By varying the spatial resolution from 10 μm down to 500 nm, sharp photoluminescence lines due to the recombination of excitons confined into quantum dots could be observed at low temperature. The dot density could be as low as ≈ 109 dots/cm2, which is smaller than previously reported values by at least one order of magnitude. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
73.21.La Quantum dots
78.55.Et II-VI semiconductors
81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.35.Gg Exciton-mediated interactions

Temperature-induced phase separation in chromium films

Laxmikant Saraf, Chongmin Wang, Mark H. Engelhard, and Donald R. Baer

Appl. Phys. Lett. 82, 2230 (2003); http://dx.doi.org/10.1063/1.1565686 (3 pages) | Cited 5 times

Online Publication Date: 2 April 2003

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Vacuum evaporation of chromium on Si(100) results in an interfacial nanophase layer followed by a mixed grain region. In this work, the mixed grain region in chromium is nearly transformed into a single-phase region, which resulted in a maximum phase separation between the nano-δ-A15 phase and bulk α-bcc chromium. It is achieved by creating a temperature gradient across the chromium–silicon interface by using rapid evaporation at a growth rate of ∼3 μm/min at a source-to-substrate (SS) distance of 2 cm. Separately grown nanophase chromium films at SS distance of 32 cm show a predominant δ-A15 phase. Short-SS-distance rapid evaporation has the potential to produce selective phase separation by combining the temperature gradient with interfacial stress. © 2003 American Institute of Physics.
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68.55.Nq Composition and phase identification
64.75.-g Phase equilibria
68.35.Gy Mechanical properties; surface strains
68.35.Fx Diffusion; interface formation

Mechanism map for a misfitting film on a viscous substrate

N. Sridhar, B. N. Cox, and D. J. Srolovitz

Appl. Phys. Lett. 82, 2233 (2003); http://dx.doi.org/10.1063/1.1565681 (3 pages) | Cited 1 time

Online Publication Date: 2 April 2003

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Compressively stressed elastic films bonded to a viscous interlayer that separates the film from the substrate can experience stress relief by one of several mechanisms: buckling, in-plane expansion at free edges, or delamination from free edges. Here, results for edge relaxation and delamination are combined with prior work on buckling to provide a comprehensive map showing how the dominant stress relief and failure mechanisms depend on geometrical and material parameters. The mechanism map is constructed by comparing the characteristic relaxation times for each relaxation mechanism. The map provides the basis for simple engineering design rules to achieve a preferred failure mechanism. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties

Determination of radiation exposure history of common materials and computer hardware by using atomic (and magnetic force) microscopy

J. Sharma, J. P. Teter, R. J. Abbundi, and N. A. Guardala

Appl. Phys. Lett. 82, 2236 (2003); http://dx.doi.org/10.1063/1.1565184 (3 pages)

Online Publication Date: 2 April 2003

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Defects produced by ionizing radiation are smaller than a micrometer and are unobservable in an optical microscope. An atomic force microscope was utilized to reveal their counts and structure in common materials like mica, silicon, organic solids, polymers, sugar, quartz, and calcite. A magnetic force microscope has shown the damage of radiation on computer hard disks. The present work shows that exposure to radioactive material leaves a permanent record, which can be read for dosimetric or forensic purposes by using atomic force microcopy on common objects or a magnetic force microscope on magnetic media.
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68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
61.80.-x Physical radiation effects, radiation damage
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
29.25.Rm Sources of radioactive nuclei
07.79.Pk Magnetic force microscopes
61.80.Ed γ-ray effects
07.79.Lh Atomic force microscopes

Diffusion barrier properties of tungsten nitride films grown by atomic layer deposition from bis(tert-butylimido)bis(dimethylamido)tungsten and ammonia

Jill S. Becker and Roy G. Gordon

Appl. Phys. Lett. 82, 2239 (2003); http://dx.doi.org/10.1063/1.1565699 (3 pages) | Cited 47 times

Online Publication Date: 2 April 2003

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Highly uniform, smooth, and conformal coatings of tungsten nitride (WN) were synthesized by atomic layer deposition (ALD) from vapors of bis(tert-butylimido)bis(dimethylamido)tungsten and ammonia. The films are shiny, silver colored, and electrically conducting. The films were amorphous as deposited. 100% step coverage was obtained inside holes with aspect ratios greater than 40:1. WN films as thin as 1.5 nm proved to be good barriers to diffusion of copper for temperatures up to 600 °C. Annealing for 30 min at temperatures above 725 °C converted the WN to pure, polycrystalline tungsten metal. ALD of copper onto the surface of the WN produced strongly adherent copper films that could be used as “seed” layers for chemical vapor deposition or electrodeposition of thicker copper coatings. © 2003 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Ls Metallization, contacts, interconnects; device isolation
81.40.Gh Other heat and thermomechanical treatments

In incorporation during the growth of quaternary III-nitride compounds by plasma-assisted molecular beam epitaxy

E. Monroy, N. Gogneau, D. Jalabert, E. Bellet-Amalric, Y. Hori, F. Enjalbert, Le Si Dang, and B. Daudin

Appl. Phys. Lett. 82, 2242 (2003); http://dx.doi.org/10.1063/1.1566465 (3 pages) | Cited 21 times

Online Publication Date: 2 April 2003

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Epitaxial growth of quaternary AlGaInN compounds by plasma-assisted molecular beam epitaxy has been demonstrated. Two-dimensional growth is achieved under In excess, with an In film segregating at the growth front. The maximum In incorporation is significantly affected by the substrate temperature and the Al mole fraction of the alloy. This behavior has been attributed to the enhancement of In segregation due to the high binding energy of AlN compared to InN and GaN. © 2003 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
52.77.Dq Plasma-based ion implantation and deposition
68.35.Dv Composition, segregation; defects and impurities

Molecular beam epitaxy growth of GaAs1−xBix

S. Tixier, M. Adamcyk, T. Tiedje, S. Francoeur, A. Mascarenhas, Peng Wei, and F. Schiettekatte

Appl. Phys. Lett. 82, 2245 (2003); http://dx.doi.org/10.1063/1.1565499 (3 pages) | Cited 99 times

Online Publication Date: 2 April 2003

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GaAs1−xBix epilayers with bismuth concentrations up to x = 3.1% were grown on GaAs by molecular beam epitaxy. The Bi content in the films was measured by Rutherford backscattering spectroscopy. X-ray diffraction shows that GaAsBi is pseudomorphically strained to GaAs but that some structural disorder is present in the thick films. The extrapolation of the lattice constant of GaAsBi to the hypothetical zincblende GaBi alloy gives 6.33±0.06 Å. Room-temperature photoluminescence of the GaAsBi epilayers is obtained and a significant redshift in the emission of GaAsBi of ∼ 84 meV per percent Bi is observed. © 2003 American Institute of Physics.
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68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
78.66.Fd III-V semiconductors
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Determination of the composition of lithium tantalate crystals by zero-birefringence measurements

Ch. Bäumer, D. Berben, K. Buse, H. Hesse, and J. Imbrock

Appl. Phys. Lett. 82, 2248 (2003); http://dx.doi.org/10.1063/1.1566100 (3 pages) | Cited 3 times

Online Publication Date: 2 April 2003

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We present an approach to determine the exact composition of lithium tantalate (LiTaO3) crystals by measuring the temperature where the birefringence disappears. Various samples with compositions ranging from the congruently melting to the stoichiometric one have been prepared by vapor transport equilibration treatments and are investigated. The sensitivity is as high as 1.5 °C/0.01 mol % Li2O. The relative accuracy is better than 0.01 mol %, while the absolute accuracy is limited by the calibration. © 2003 American Institute of Physics.
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78.20.Fm Birefringence
61.66.Bi Elemental solids
61.66.Dk Alloys

Effect of overgrowth temperature on shape, strain, and composition of buried Ge islands deduced from x-ray diffraction

J. Stangl, A. Hesse, V. Holý, Z. Zhong, G. Bauer, U. Denker, and O. G. Schmidt

Appl. Phys. Lett. 82, 2251 (2003); http://dx.doi.org/10.1063/1.1565695 (3 pages) | Cited 21 times

Online Publication Date: 2 April 2003

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We have investigated a series of samples containing SiGe islands capped at different growth temperatures. A layer of islands formed by deposition of 5 ML of pure Ge was capped with Si, deposited at temperatures of 460, 540, and 630 °C, respectively. The Ge composition profile and the shape of the buried islands are deduced from x-ray diffraction data. While for capping at high substrate temperatures a significant dilution of the Ge content and a flattening of the islands occur, capping at low temperatures maintains a high aspect ratio and a high Ge content of the islands. The maximum in-plane strain in the island remains as high as 0.005 for capping at low temperatures. © 2003 American Institute of Physics.
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68.55.Nq Composition and phase identification
81.16.Dn Self-assembly
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.60.Bs Mechanical and acoustical properties

Phosphorus and boron diffusion in silicon under equilibrium conditions

J. S. Christensen, H. H. Radamson, A. Yu. Kuznetsov, and B. G. Svensson

Appl. Phys. Lett. 82, 2254 (2003); http://dx.doi.org/10.1063/1.1566464 (3 pages) | Cited 13 times

Online Publication Date: 2 April 2003

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The intrinsic diffusion of phosphorus and boron in high-purity epitaxial silicon films has been studied. Phosphorus diffusion in a wide temperature range (810 to 1100 °C) revealed diffusion coefficients with an Arrhenius behavior exhibiting an activation energy of 2.74±0.07 eV and a pre-exponential factor of (8±5)×10−4 cm2/s. In the temperature range of 810 to 1050 °C, boron was found to diffuse with an activation energy of 3.12±0.04 eV and a pre-exponential factor of 0.06±0.02 cm2/s. These results differ from those of many previous studies, but this deviation may to a large extent be attributed to slow transients before equilibrium concentrations of point defects are established at temperatures below ∼1000 °C. Despite a similar diffusion mechanism mediated by Si self-interstitials, P exhibits a lower activation energy than B because of stronger bonding to the Si self-interstitial. © 2003 American Institute of Physics.
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68.60.Wm Other nonelectronic physical properties
66.30.J- Diffusion of impurities
61.72.J- Point defects and defect clusters

Pressure-induced phase of NaAlH4: A potential candidate for hydrogen storage?

P. Vajeeston, P. Ravindran, R. Vidya, H. Fjellvåg, and A. Kjekshus

Appl. Phys. Lett. 82, 2257 (2003); http://dx.doi.org/10.1063/1.1566086 (3 pages) | Cited 56 times

Online Publication Date: 2 April 2003

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The electronic structure and structural stability of the technologically interesting material NaAlH4 are studied using an ab initio projected augmented plane-wave method for different possible structure modifications. We predict that α-NaAlH4 converts to β-NaAlH4 at 6.43 GPa with a 4 % volume contraction. Both modifications have nonmetallic character with finite energy gaps, the calculated band gap for β-NaAlH4 being almost half of that for the α phase. β-NaAlH4 stores hydrogen more volume efficient than the α phase and would if stabilized at ambient conditions be an interesting candidate for further studies with regard to hydrogen absorption/desorption efficiency. © 2003 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.20.Ps Other inorganic compounds

Dielectric functions (1 to 5 eV) of wurtzite MgxZn1−xO (x ⩽ 0.29) thin films

R. Schmidt, B. Rheinländer, M. Schubert, D. Spemann, T. Butz, J. Lenzner, E. M. Kaidashev, M. Lorenz, A. Rahm, H. C. Semmelhack, and M. Grundmann

Appl. Phys. Lett. 82, 2260 (2003); http://dx.doi.org/10.1063/1.1565185 (3 pages) | Cited 82 times

Online Publication Date: 2 April 2003

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The optical dielectric functions for polarization perpendicular and parallel to the c-axis (optical axis) of pulsed-laser-deposition grown wurtzite MgxZn1−xO (0 ⩽ x ⩽ 0.29) thin films have been determined at room temperature using ellipsometry for photon energies from 1 to 5 eV. The dielectric functions reveal strong excitonic contributions for all Mg concentrations x. The band gap energies (E0A=3.369 eV for ZnO to 4.101 eV for x=0.29) show a remarkable blueshift. The exciton binding energy (61 meV for ZnO) decreases to approximately 50 meV for x≈0.17 and increases to approximately 58 meV for x=0.29. In contrast to ZnO, the MgxZn1−xO alloys are found uniaxial negative below the band gap energy, opposite to previously reported results. © 2003 American Institute of Physics.
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78.66.Li Other semiconductors
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Fg Pulsed laser ablation deposition
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.20.Nr Semiconductor compounds
71.15.Nc Total energy and cohesive energy calculations
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Decoration effects as origin of dislocation-related charges in gallium nitride layers investigated by scanning surface potential microscopy

A. Krtschil, A. Dadgar, and A. Krost

Appl. Phys. Lett. 82, 2263 (2003); http://dx.doi.org/10.1063/1.1565687 (3 pages) | Cited 18 times

Online Publication Date: 2 April 2003

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The electrical charge state of threading dislocations in differently doped GaN is investigated by scanning surface potential microscopy in conjunction with tapping mode atomic force microscopy. The dislocations are found to be either negatively charged or neutral depending on the type of doping atoms in the layers, i.e., Mg acceptors, Si donors, or without intentional doping. The results are interpreted in terms of decoration of the dislocations with other defects resulting in a partial compensation of the core charge by the accumulated charges around. © 2003 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Yx Interaction between different crystal defects; gettering effect
68.37.Ps Atomic force microscopy (AFM)

Fermi level on hydrogen terminated diamond surfaces

B. Rezek, C. Sauerer, C. E. Nebel, M. Stutzmann, J. Ristein, L. Ley, E. Snidero, and P. Bergonzo

Appl. Phys. Lett. 82, 2266 (2003); http://dx.doi.org/10.1063/1.1564293 (3 pages) | Cited 36 times

Online Publication Date: 2 April 2003

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Atomic force microscopy and Kelvin probe experiments are applied to characterize hydrogen terminated patterns contacted with gold and aluminum on (100) diamond surfaces. On hydrogen terminated diamond the work function of 4.9 eV is detected, with an accuracy of about 0.1 eV. Taking into account the negative electron affinity of −1.3 eV and a band gap of 5.5 eV the Fermi energy is 0.7 eV deep in the valence band. Illumination of the sample results in a shift of the surface Fermi level by as much as 0.2 eV. This is attributed to a surface photovoltage effect. © 2003 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
73.25.+i Surface conductivity and carrier phenomena
72.40.+w Photoconduction and photovoltaic effects
68.37.Ps Atomic force microscopy (AFM)

In situ preparation and interface characterization of TiO2/Cu2S heterointerface

Guangming Liu, T. Schulmeyer, A. Thissen, A. Klein, and W. Jaegermann

Appl. Phys. Lett. 82, 2269 (2003); http://dx.doi.org/10.1063/1.1565507 (3 pages) | Cited 16 times

Online Publication Date: 2 April 2003

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The electronic structures and interface properties of the TiO2/Cu2S interface have been in situ studied after each growth step by x-ray and ultraviolet photoelectron spectroscopy. The p-doped Cu2S films (BEVBM = 0.1 eV) were grown on the highly n-doped chemical vapor deposition prepared TiO2 (BEVBM = 3.4 eV) films by thermal evaporation in a multistep growth procedure. The conduction band offset (0.7 eV), valence band offset (2.9 eV) and interface dipole (0.5 eV) were determined based on the quantitative examination of band bending occurring in the Cu2S films at higher coverage, leading to a staggered energy level configuration. © 2003 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Jv Interfaces; heterostructures; nanostructures
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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