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11 Jul 2005

Volume 87, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 024103 (2005); http://dx.doi.org/10.1063/1.1984098 (3 pages)

A. Dupuis, J. Léopoldès, D. G. Bucknall, and J. M. Yeomans
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Examining microcavity organic light-emitting devices having two metal mirrors

Chun-Liang Lin, Hao-Wu Lin, and Chung-Chih Wu

Appl. Phys. Lett. 87, 021101 (2005); http://dx.doi.org/10.1063/1.1988985 (3 pages) | Cited 65 times

Online Publication Date: 5 July 2005

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Optical characteristics of microcavity organic light-emitting devices (OLEDs) having two metal mirrors are examined. Analyses show that a high-reflection back mirror and a low-loss high-reflection exit mirror are essential for such microcavity devices to obtain luminance enhancement relative to conventional noncavity devices. An enhancement of 2 in cd/A efficiencies has been experimentally achieved for microcavity top-emitting OLEDs using an exit mirror composing thin metal and dielectric capping. The capping layer in the composite mirror plays the role of enhancing reflection and reducing absorption loss, rather than enhancing transmission.
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85.60.Jb Light-emitting devices
42.79.Bh Lenses, prisms and mirrors

Strong light-matter coupling at room temperature in simple geometry GaN microcavities grown on silicon

F. Semond, I. R. Sellers, F. Natali, D. Byrne, M. Leroux, J. Massies, N. Ollier, J. Leymarie, P. Disseix, and A. Vasson

Appl. Phys. Lett. 87, 021102 (2005); http://dx.doi.org/10.1063/1.1994954 (3 pages) | Cited 33 times

Online Publication Date: 5 July 2005

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The reflectance spectra of simple design GaN-based microcavities have been studied in the 5 K–300 K range. The epitaxial structure consists of the silicon substrate and the stack of buffer layers as the back mirror, a GaN active layer, and a 100 Å thick aluminium layer as the top mirror. Active layer thicknesses of λ/2, λ, or 3λ/2 were investigated. The samples with GaN thicknesses λ/2 and λ display an anticrossing behavior between the cavity and exciton modes, with measured Rabi splittings of 47 and 60 meV, respectively, both at 5 K and room temperature.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.35.-y Excitons and related phenomena

Thermally widely tunable laser diodes with distributed feedback

R. Todt, T. Jacke, R. Meyer, and M.-C. Amann

Appl. Phys. Lett. 87, 021103 (2005); http://dx.doi.org/10.1063/1.1993760 (3 pages) | Cited 5 times

Online Publication Date: 6 July 2005

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A thermally widely tunable buried heterostructure laser diode with distributed feedback (DFB) is demonstrated. This device requires only two tuning currents for wide quasicontinuous wavelength tuning, thereby facilitating easy and fast device calibration and control. Furthermore, being based on regular DFB laser fabrication technology, it is readily manufacturable. By using window structures instead of cleaved facets plus antireflection coatings, a regular tuning behavior has been achieved for a DFB-like widely tunable laser diode with only two tuning currents. The laser diode covers the wavelength range between 1552 and 1602 nm. Requiring side-mode suppression ratio and output power above 30 dB and 10 mW, respectively, a wavelength range of 43 nm is accessible.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
06.20.F- Units and standards

Time-resolved chirp in an InAs/InP quantum-dash optical amplifier operating with 10 Gbit/s data

D. Hadass, V. Mikhelashvili, G. Eisenstein, A. Somers, S. Deubert, W. Kaiser, J. P. Reithmaier, A. Forchel, D. Finzi, and Y. Maimon

Appl. Phys. Lett. 87, 021104 (2005); http://dx.doi.org/10.1063/1.1994947 (3 pages) | Cited 9 times

Online Publication Date: 6 July 2005

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We describe time-resolved chirp measurements in InAs/InP quantum-dash optical amplifiers operating at 1550 nm. We highlight the roles of gain saturation and of the saturating pulse duration relative to the gain recovery time. Using 10 Gbit/s data, we demonstrate a low transient α parameter of less than one which causes negative chirp at the leading edge and positive chirp during the trailing edge of the input pulse.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.-k Nonlinear optics

Achieving epitaxy and intense luminescence in Ge/Rb-implanted α-quartz

P. K. Sahoo, S. Gąsiorek, K. P. Lieb, K. Arstila, and J. Keinonen

Appl. Phys. Lett. 87, 021105 (2005); http://dx.doi.org/10.1063/1.1994953 (3 pages) | Cited 5 times

Online Publication Date: 6 July 2005

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The luminescence properties of ion-beam doped silica and quartz depend sensitively on the ion species and fluence and the thermal processing during and after ion implantation. In an attempt to achieve high luminescence intensity and full planar recrystallization of α-quartz, we studied double Ge/Rb-ion implantation, where the Rb ions serve as a catalyst only. Synthetic α-quartz samples were irradiated with 175 keV Rb ions and subsequently with 120 keV Ge ions with fluences of 1×1014–1×1016 ions/cm2 and postannealed at 1170 K in air. A comparative analysis of the epitaxy, migration of the implanted ions, and cathodoluminescence (CL) were carried out. The CL spectra exhibit three strong emission bands in the blue/violet range at 2.95, 3.25, and 3.53 eV, which were assigned to Rb- and/or Ge-related defect centers. For up to 1015 implanted Ge ions/cm2, large fraction (75%) of the Ge atoms reach substitutional Si sites after the epitaxy.
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42.70.Ce Glasses, quartz
78.60.Hk Cathodoluminescence, ionoluminescence
61.80.Jh Ion radiation effects
61.72.up Other materials
81.40.Gh Other heat and thermomechanical treatments
78.40.Ha Other nonmetallic inorganics

Rapid switching in a dual-frequency hybrid aligned nematic liquid crystal cell

S. A. Jewell, T. S. Taphouse, and J. R. Sambles

Appl. Phys. Lett. 87, 021106 (2005); http://dx.doi.org/10.1063/1.1992672 (3 pages) | Cited 13 times

Online Publication Date: 8 July 2005

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We report the optical characterization of a dual-frequency hybrid aligned nematic (HAN) liquid crystal cell driven between two states using a multiple-frequency sinusoidal pulse. The complex dynamic director structure formed during the fast switching process is resolved in unprecedented detail on a submillisecond time scale. The results reveal backflow effects and a total switching time that is substantially faster than that achievable with conventional HAN cells.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Kr Display devices, liquid-crystal devices

Tunable 30-femtosecond pulses across the deep ultraviolet

Askat E. Jailaubekov and Stephen E. Bradforth

Appl. Phys. Lett. 87, 021107 (2005); http://dx.doi.org/10.1063/1.1992655 (3 pages) | Cited 29 times

Online Publication Date: 8 July 2005

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Intense femtosecond pulses in the deep ultraviolet are generated by phase-matched four-wave mixing in an argon-filled hollow waveguide using 100-fs pulses from a commercial Ti:sapphire regenerative amplifier. Despite the long duration driving pulses, pulses as short as 25 fs with energies of >5 μJ at 266 nm are produced after a simple double-pass prism compressor. In combination with an infrared optical parametric amplifier, tunable pulses are obtained over the 224–240 nm range with energies exceeding 1 μJ, bandwidths of 5 nm and typical compressed pulsewidths of 31 fs. Excellent mode and stability make this a promising source for deep ultraviolet pump-probe experiments.
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42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Rz Doped-insulator lasers and other solid state lasers
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Lm Parametric down conversion and production of entangled photons

Tuning photonic crystal nanocavity modes by wet chemical digital etching

K. Hennessy, A. Badolato, A. Tamboli, P. M. Petroff, E. Hu, M. Atatüre, J. Dreiser, and A. Imamoğlu

Appl. Phys. Lett. 87, 021108 (2005); http://dx.doi.org/10.1063/1.1992656 (3 pages) | Cited 63 times

Online Publication Date: 8 July 2005

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We have developed a wet chemical digital etching technique for tuning the resonant wavelengths of photonic crystal (PC) nanocavities over a wide range of 80 nm in precise 2–3 nm steps while preserving high cavity quality factors. In one tuning step, a few monolayers of material are removed from the cavity surface by etching a self-formed native oxide in 1 mol citric acid. Due to the self-limiting oxide thickness, total tuning range is based only on the number of etch steps, resulting in a highly controlled, digital tuning ability. We have characterized the tuning behavior of GaAs PC defect cavities of both square and triangular lattice symmetry and proven the effectiveness of this method by tuning a mode into resonance with the charged exciton, and then later the biexciton, transition of a single InAs/GaAs self-assembled quantum dot.
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42.70.Qs Photonic bandgap materials
42.65.-k Nonlinear optics
81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
71.35.Pq Charged excitons (trions)

Mechanisms of refractive index modification during femtosecond laser writing of waveguides in alkaline lead-oxide silicate glass

F. Vega, J. Armengol, V. Diez-Blanco, J. Siegel, J. Solis, B. Barcones, A. Pérez-Rodríguez, and P. Loza-Alvarez

Appl. Phys. Lett. 87, 021109 (2005); http://dx.doi.org/10.1063/1.1994927 (3 pages) | Cited 11 times

Online Publication Date: 8 July 2005

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We report on the mechanisms responsible for the formation of optical waveguides upon femtosecond laser irradiation of an alkaline lead-oxide silicate glass. MicroRaman spectroscopy and nonlinear fluorescence were employed to probe the local glass network structure and the formation of optically active defects respectively. At low laser pulse energies, the laser modified region is formed by a single light guiding region, whereas for pulses above 14 μJ the modified region is formed by a central dark zone, which does not guide light, accompanied by light guiding zones located in the surrounding of the dark one. This behavior is different from that observed in common silica glass systems but agrees with recent results obtained in phosphate and heavy metal oxide glasses. However, our results show that, unlike the latter glass, local densification of the glass occurs in the whole laser modified region, i.e., in the dark and the guiding zones. The suppression of light guiding in the dark region is explained by a high density of absorbing color centers.
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42.79.Gn Optical waveguides and couplers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.70.Ce Glasses, quartz
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.55.Hx Other solid inorganic materials
61.72.J- Point defects and defect clusters
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Tunable magnetic fluid grating by applying a magnetic field

Shengli Pu, Xianfeng Chen, Lijun Chen, Weijun Liao, Yuping Chen, and Yuxing Xia

Appl. Phys. Lett. 87, 021901 (2005); http://dx.doi.org/10.1063/1.1991984 (3 pages) | Cited 18 times

Online Publication Date: 5 July 2005

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A kind of tunable magnetic fluid grating is developed in this letter. The operating principle of the tunable magnetic fluid grating is analyzed theoretically. When the absorption coefficient modulation of the grating is not too large, the energy of the zeroth-order diffracted light can be transferred to that of the higher-order completely and vice versa. Experiments are done to investigate the tunable diffraction properties of the magnetic fluid grating, and the transfer of the energy of the zeroth-order diffracted light to that of the higher-order is apparent.
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42.79.Dj Gratings
42.25.Fx Diffraction and scattering
42.25.Bs Wave propagation, transmission and absorption

Diffusion of nitrogen in silicon

N. Fujita, R. Jones, J. P. Goss, P. R. Briddon, T. Frauenheim, and S. Öberg

Appl. Phys. Lett. 87, 021902 (2005); http://dx.doi.org/10.1063/1.1991996 (3 pages) | Cited 11 times

Online Publication Date: 7 July 2005

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We use local density functional theory to investigate the diffusion of nitrogen dimers in silicon. We investigate several trajectories for the diffusing dimer finding an alternative one whose barrier is 2.69 eV and in close agreement with experimental diffusion data carried out at high temperature. We suggest that recent reports of a low barrier of 1.45 eV found from studies of dislocation unlocking are to be understood from the interaction of nitrogen dimers with interstitials or vacancies released by the dislocation.
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66.30.J- Diffusion of impurities
61.72.J- Point defects and defect clusters
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Effect of multilayer barriers on the optical properties of GaInNAs single quantum-well structures grown by metalorganic vapor phase epitaxy

H. D. Sun, A. H. Clark, S. Calvez, M. D. Dawson, K. S. Kim, T. Kim, and Y. J. Park

Appl. Phys. Lett. 87, 021903 (2005); http://dx.doi.org/10.1063/1.1993758 (3 pages) | Cited 6 times

Online Publication Date: 7 July 2005

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We report on the effects of combined strain-compensating and strain-mediating layers of various widths on the optical properties of 1.3 μm GaInNAs∕GaAs single quantum well structures grown by metalorganic vapor phase epitaxy (MOVPE). While the emission wavelength of GaInNAs∕GaAs quantum wells can be redshifted by the adoption of strain-compensated GaNAs layers, the material quality is degraded by the increased stress at the well∕barrier interface. This detrimental effect can be cured by inserting a strain-mediating InGaAs layer between them. Contrary to what is expected, however, the emission wavelength is blueshifted by the insertion of the InGaAs layer, which is attributed to the reduced N incorporation due to the improved interface quality. Our results indicate that the optical properties of MOVPE-grown GaInNAs∕GaAs quantum wells can be optimized in quantum efficiency and emission wavelength by combination of strain-compensating and strain-mediating layers with suitable characteristics.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.Fg Quantum wells

Microscale application of column theory for high resolution force and displacement sensing

B. A. Samuel, A. V. Desai, and M. A. Haque

Appl. Phys. Lett. 87, 021904 (2005); http://dx.doi.org/10.1063/1.1989440 (3 pages) | Cited 4 times

Online Publication Date: 7 July 2005

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We present the design, fabrication, and experimental validation of a device which exploits the amplification of displacement and attenuation of structural stiffness in the post-buckling deformation of slender columns to obtain pico-Newton force and nanometer displacement resolution, even under an optical microscope. The extremely small size, purely mechanical sensing scheme and vacuum compatibility of the instrument makes it compatible with existing visualization tools of nanotechnology. The instrument has a wide variety of potential applications ranging from electro-mechanical characterization of one dimensional solids to single biological cells.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Pz Instruments for strain, force, and torque
46.32.+x Static buckling and instability

Suppressing the thermal lens effect by magnetic-field-induced mass transfer and phase separation in a magnetic fluid

Shengli Pu, Xianfeng Chen, Lijun Chen, Weijun Liao, Yuping Chen, and Yuxing Xia

Appl. Phys. Lett. 87, 021905 (2005); http://dx.doi.org/10.1063/1.1996841 (3 pages) | Cited 5 times

Online Publication Date: 8 July 2005

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A method for suppressing the thermal lens effect in a magnetic fluid is proposed in this letter. When an external parallel magnetic field is applied, the thermal lens effect is weakened, and the degree of the divergence of the laser beam after passing through the magnetic fluid decreases. By experimental measurement and theoretical analysis, we assign this phenomenon to two physical mechanisms: the magnetic-field-induced mass transfer and phase separation in the magnetic fluid. With this method, the quality of the magnetic-fluid-based potential photonic devices can be improved.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
75.50.Mm Magnetic liquids
64.75.-g Phase equilibria

Eu locations in Eu-doped InGaN/GaN quantum dots

Thomas Andreev, Eva Monroy, Bruno Gayral, Bruno Daudin, Nguyen Quang Liem, Yuji Hori, Mitsuhiro Tanaka, Osamu Oda, and Daniel Le Si Dang

Appl. Phys. Lett. 87, 021906 (2005); http://dx.doi.org/10.1063/1.1992667 (3 pages) | Cited 9 times

Online Publication Date: 8 July 2005

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We report on the photoluminescence and photoluminescence excitation studies of Eu-doped wurtzite InGaN quantum dots (QDs) embedded in a GaN matrix grown by plasma-assisted molecular-beam epitaxy. The location of Eu3+ ions either in InGaN QDs or in the GaN spacing layer is assigned by comparing the different behaviors of the math→math emission around 620 nm under various photoexcitation energies and temperatures to those observed in Eu-doped GaN/AlN QDs and a Eu-doped GaN thick layer.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
61.72.uj III-V and II-VI semiconductors

Low-temperature metalorganic chemical vapor deposition of luminescent manganese-doped aluminum nitride films

A. Sato, K. Azumada, T. Atsumori, and K. Hara

Appl. Phys. Lett. 87, 021907 (2005); http://dx.doi.org/10.1063/1.1992669 (3 pages) | Cited 6 times

Online Publication Date: 8 July 2005

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Mn-doped AlN films have been prepared at a substrate temperature of 400 °C by metalorganic chemical vapor deposition using bismethylcyclopentadienyl manganese as a Mn source. The Mn concentration in the films (CMn) was controlled extensively in the region from 2×1018 to 1×1021 cm−3. The samples showed red-orange photoluminescence (PL) and cathodoluminescence (CL) originated from the transition of 3d-electrons in Mn ions incorporated in AlN. The maximum emission intensities were observed at different CMn for PL and CL, which was discussed in terms of the excitation mechanism of the Mn center. The electroluminescence (EL) property was also investigated by fabricating thin-film EL devices with the AlN:Mn active layer on glass substrates.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
78.60.Fi Electroluminescence

Effects of growth temperature on the structural and optical properties of 1.55 μm GaInNAsSb quantum wells grown on GaAs

Seth R. Bank, Homan B. Yuen, Mark A. Wistey, Vincenzo Lordi, Hopil P. Bae, and James S. Harris

Appl. Phys. Lett. 87, 021908 (2005); http://dx.doi.org/10.1063/1.1993772 (3 pages) | Cited 8 times

Online Publication Date: 8 July 2005

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We investigate the effects of growth temperature on the structural and optical properties of GaInNAsSb single quantum wells grown by molecular beam epitaxy. Peak room-temperature photoluminescence occurred at 1.65 μm as-grown and at 1.55 μm under optimal annealing conditions. Excellent room-temperature optical efficiency was observed from samples grown between 420 and 460 °C, with a maximum at 440 °C. However, luminescence was degraded approximately two orders of magnitude for a sample grown at 470 °C. High-resolution x-ray diffraction showed substantial structural degradation and a reduction in strain for the 470 °C sample. Low temperature photoluminescence measurements were also employed to study localization and quenching effects; both became more severe with increasing growth temperature.
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81.05.Ea III-V semiconductors
81.07.St Quantum wells
61.72.Cc Kinetics of defect formation and annealing
68.65.Fg Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.De Quantum wells
78.55.Cr III-V semiconductors
81.40.Gh Other heat and thermomechanical treatments

Bulk cohesive energy and surface tension from the size-dependent evaporation study of nanoparticles

K. K. Nanda

Appl. Phys. Lett. 87, 021909 (2005); http://dx.doi.org/10.1063/1.1994958 (3 pages) | Cited 23 times

Online Publication Date: 8 July 2005

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In this letter, it is shown that the bulk cohesive energy (EB) and bulk surface tension (γ) can be deduced from the size-dependent evaporation (SDE) study of free nanoparticles. The surface tension of nanoparticles (γn) is obtained by analyzing SDE data on the basis of the Kelvin equation, while EB is obtained by reanalyzing the SDE data. By comparing the size-dependent melting and the SDE of nanoparticles, γ is evaluated.
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68.03.Cd Surface tension and related phenomena
64.70.F- Liquid-vapor transitions
61.46.-w Structure of nanoscale materials
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Electron transport in ZnO thin films

T. Makino, Y. Segawa, A. Tsukazaki, A. Ohtomo, and M. Kawasaki

Appl. Phys. Lett. 87, 022101 (2005); http://dx.doi.org/10.1063/1.1991994 (3 pages) | Cited 35 times

Online Publication Date: 5 July 2005

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Epitaxial n-type ZnO films grown by a laser molecular-beam epitaxy method were investigated by the temperature-dependent Hall-effect technique. The 300 K carrier concentration and mobility were about ns ∼ 1016 cm−3 and 440 cm2/V s, respectively. Transport characteristics are calculated by solving the Boltzmann transport equation using a variational method. Mobility limit of 430 cm2/V s was calculated at 300 K. The temperature dependence of the mobility for an undoped film is calculated and agrees favorably well with experimental data if physical parameters are chosen so as to approach those. In the experimental “mobility versus concentration” curve, unusual phenomenon was observed, i.e., mobilities at ns ∼ 5×1018 cm−3 are significantly smaller than those at higher densities above ∼ 1020 cm−3. It is qualitatively explained in terms of electron-plasmon interaction.
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73.61.Ga II-VI semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.05.Dz II-VI semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Mx High-frequency effects; plasma effects
73.43.Lp Collective excitations

Plasma wave resonant detection of femtosecond pulsed terahertz radiation by a nanometer field-effect transistor

F. Teppe, D. Veksler, V. Yu. Kachorovski, A. P. Dmitriev, X. Xie, X.-C. Zhang, S. Rumyantsev, W. Knap, and M. S. Shur

Appl. Phys. Lett. 87, 022102 (2005); http://dx.doi.org/10.1063/1.1952578 (3 pages) | Cited 28 times

Online Publication Date: 7 July 2005

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We report on the room-temperature, resonant detection of femtosecond pulsed terahertz radiation obtained by optical rectification in a ZnTe crystal. The detection was realized using a 250 nm gate length GaAs/AlGaAs heterostructure field-effect transistor. We show that physical mechanism of the detection is related to the plasma waves excited in the transistor channel. The detection is strongly enhanced by increasing the drain current and driving the transistor into the plasma wave instability region. Our results clearly show that plasma wave nanometer transistors can be efficient and fast detectors for terahertz spectroscopic imaging based on the femtosecond pulsed THz sources.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
85.30.Tv Field effect devices

Room-temperature semiconductor heterostructure refrigeration

K. A. Chao, Magnus Larsson, and A. G. Mal’shukov

Appl. Phys. Lett. 87, 022103 (2005); http://dx.doi.org/10.1063/1.1992651 (3 pages) | Cited 6 times

Online Publication Date: 8 July 2005

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With the proper design of semiconductor tunneling barrier structures, we can inject low-energy electrons via resonant tunneling, and take out high-energy electrons via a thermionic process. This is the operation principle of our semiconductor heterostructure refrigerator (SHR) without the need of applying a temperature gradient across the device. Even for the bad thermoelectric material AlGaAs, our calculation shows that at room temperature, the SHR can easily lower the temperature by 5–7 K. Such devices can be fabricated with the present semiconductor technology. Besides its use as a kitchen refrigerator, the SHR can efficiently cool microelectronic devices.
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07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Controlled band offset in (Gd2O3)1−x(SiO2)x(0 ⩽ x ⩽ 1)/n–GaAs (001) structure

Jun-Kyu Yang and Hyung-Ho Park

Appl. Phys. Lett. 87, 022104 (2005); http://dx.doi.org/10.1063/1.1992652 (3 pages) | Cited 9 times

Online Publication Date: 8 July 2005

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This letter investigates the chemistry and energy band structure of (Gd2O3)1−x(SiO2)x(0 ⩽ x ⩽ 1) films grown on n-GaAs (001). Dielectric band gap and interfacial band alignment of Gd2O3 films were modified by compounding with SiO2. Binding energy shift of core level was observed from different electronegativity of second nearest-neighbor element. Controlled parameters of energy band structure were systematically characterized by valence band, absorption, and energy loss spectra. Assuming no Fermi level pinning in the midgap of n-GaAs, band offset values represent almost linear dependency on the concentration of SiO2. The correlation of band offset with the electrical properties, as probed by capacitance and leakage current measurements, was also discussed.
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73.20.At Surface states, band structure, electron density of states
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Thermally stable visible-blind diamond photodiode using tungsten carbide Schottky contact

Meiyong Liao, Yasuo Koide, and Jose Alvarez

Appl. Phys. Lett. 87, 022105 (2005); http://dx.doi.org/10.1063/1.1992660 (3 pages) | Cited 32 times

Online Publication Date: 8 July 2005

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We have developed a thermally stable, deep-ultraviolet (DUV) photodiode using tungsten carbide (WC) Schottky and Ti/WC ohmic contacts for a boron-doped homoepitaxial p-diamond epilayer. Effects of thermal annealing in an argon ambient on the electrical and photoresponse properties were investigated. Annealing at temperatures up to 550 °C improves the rectifying current-voltage characteristics, resulting in a dramatic enhancement of DUV responsivity at 220 nm by a factor of 4×103. A blind ratio as large as 105 between DUV and visible light has been achieved at a reverse bias as small as 1 V. Development of the thermally stable WC-based Schottky and ohmic contacts provides a route for stable operation of a diamond photodetector at high temperatures.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Kk Junction diodes
85.60.Gz Photodetectors (including infrared and CCD detectors)
61.72.Cc Kinetics of defect formation and annealing
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Silver-assisted growth of NdBa2Cu3O7−δ thin films: An approach for the growth of superior quality ceramic oxide films

J. Kurian, H. Sato, T. Makimoto, and M. Naito

Appl. Phys. Lett. 87, 022501 (2005); http://dx.doi.org/10.1063/1.1991986 (3 pages)

Online Publication Date: 5 July 2005

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We have grown NdBa2Cu3O7−δ films under silver atomic flux by molecular-beam epitaxy, which show a drastic improvement in microstructure and also crystallinity leading to a 30% enhancement in critical current density. The most remarkable point is that the final film is free from silver. The key to our process in achieving a silver-free film was the use of rf-activated oxygen that oxidizes silver, nonvolatile, to silver oxide, volatile at the deposition temperature. This process enables one to utilize the beneficial effects of silver in the growth of oxide films and at the same time ensures that the final film be free from silver, which is important for high-frequency applications. This method can be used in the growth of thin films of other complex oxide materials.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
74.25.Sv Critical currents
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
61.72.-y Defects and impurities in crystals; microstructure

Demonstration of chip-to-chip transmission of single-flux-quantum pulses at throughputs beyond 100 Gbps

Yoshihito Hashimoto, Shinichi Yorozu, Tetsuro Satoh, and Toshiyuki Miyazaki

Appl. Phys. Lett. 87, 022502 (2005); http://dx.doi.org/10.1063/1.1993767 (3 pages) | Cited 13 times

Online Publication Date: 6 July 2005

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We report a demonstration of single-flux-quantum (SFQ) pulse transmission between superconductor chips at throughputs beyond 100 Gbps. A fabrication process with a high junction critical current density of 10 kA/cm2 was used to increase the operation speed of a pulse driver and receiver. The chips were flip-chip bonded on a passive microstrip carrier using small solder bumps with diameters of 30 μm. With experiments based on a ring-shaped circuit, chip-to-chip SFQ pulse transmission has been demonstrated up to 117 Gbps with an error rate of less than 10−15. The power dissipated by the driver and receiver was only 0.24 μW at 117 Gbps.
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84.30.Sk Pulse and digital circuits
85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits
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