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12 Sep 1994

Volume 65, Issue 11, pp. 1331-1468

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In situ native oxide removal from AlGaInAs surfaces by hydrogen radical treatment for molecular beam epitaxy regrowth

A. Hase, R. Gibis, H. Künzel, and U. Griebenow

Appl. Phys. Lett. 65, 1406 (1994); http://dx.doi.org/10.1063/1.112066 (3 pages) | Cited 6 times

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Removal of native oxide from Al0.24Ga0.24In0.52As layers grown lattice‐matched onto InP substrates is successfully achieved by an in situ hydrogen radical treatment prior to molecular beam epitaxy (MBE) overgrowth. Cleaning conditions using moderate substrate temperatures not necessitating a surface stabilizing arsenic flux were elaborated, which ensured complete oxide removal without deterioration of the underlying AlGaInAs material. The surface quality as assessed by high energy electron diffraction, and the quality of epitaxial layers deposited onto this surface were found to be at least equivalent to that achieved with epitaxial growth directly on InP substrates, indicating the achievement of thorough oxide removal, low residual contamination levels, and a surface smoothness adequate for MBE regrowth.
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81.65.-b Surface treatments
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Growth of high quality Ge films on Si(111) using Sb as surfactant

Mats I. Larsson, Wei‐Xin Ni, Kenneth Joelsson, and Göran V. Hansson

Appl. Phys. Lett. 65, 1409 (1994); http://dx.doi.org/10.1063/1.112067 (3 pages) | Cited 10 times

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High quality, completely relaxed Ge films have been grown on Si(111) using Sb as surfactant at the initial stage of growth. After desorbing the surface Sb layer, cusplike reflection high‐energy electron diffraction intensity oscillations indicated excellent Ge layer‐by‐layer epitaxy. High resolution x‐ray diffraction analysis showed a very high crystalline quality and well resolved thickness fringes consistent with a flat relaxed Ge layer. Chemical preferential etching experiments revealed a defect density of down to ∼3×104 cm−2.
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68.55.-a Thin film structure and morphology

Donor‐related deep level in bulk GaSb

P. S. Dutta, K. S. R. Koteswara Rao, K. S. Sangunni, H. L. Bhat, and Vikram Kumar

Appl. Phys. Lett. 65, 1412 (1994); http://dx.doi.org/10.1063/1.112975 (3 pages) | Cited 16 times

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Deep level transient spectroscopy (DLTS) and thermally stimulated capacitance (TSCAP) studies on bulk grown tellurium‐ selenium‐, and sulphur‐doped gallium antimonide reveal the presence of deep level intrinsic of the dopant species. The trap densities in Te‐ and Se‐doped samples were found to be at least two orders of magnitude lower than the shallow donor concentration. Interestingly, the DLTS spectrum of S:GaSb exhibits DX‐like nature with the trap concentration comparable to that of shallow donor concentration. However, the Te and Se related levels do not exhibit DX‐like nature. The DLTS and TSCAP results are in good agreement with each other.
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71.55.Eq III-V semiconductors

Nanometer‐structure writing on Si(100) surfaces using a non‐contact‐mode atomic force microscope

Dawen Wang, Liming Tsau, and K. L. Wang

Appl. Phys. Lett. 65, 1415 (1994); http://dx.doi.org/10.1063/1.112068 (3 pages) | Cited 19 times

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Nanometer structures were written on Si(100) surfaces by use of a non‐contact‐mode atomic force microscope. The silicon oxide was formed beneath the tip by applying a negative bias voltage between a p+ silicon tip and the samples. The writing resolution was mainly determined by the local chemical reactions induced by the tip and a minimum line width of about 10 nm was obtained, which is close to that achieved by scanning tunneling microscope and contact‐mode atomic force microscope writing.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
81.65.-b Surface treatments

Wide terrace formation during metalorganic vapor phase epitaxy of GaAs, AlAs, and AlGaAs

Masanori Shinohara, Masafumi Tanimoto, Haruki Yokoyama, and Naohisa Inoue

Appl. Phys. Lett. 65, 1418 (1994); http://dx.doi.org/10.1063/1.112069 (3 pages) | Cited 5 times

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GaAs, Al0.35Ga0.65As, and AlAs surface terrace structures formed during metalorganic vapor phase epitaxy (MOVPE) on vicinal (001) surfaces are investigated. The minimal terrace width for two‐dimensional (2‐D) nucleation for AlGaAs is almost equal to that for GaAs. In contrast, for AlAs it is reduced and the growth mode becomes three dimensional at temperatures below 580 °C. Monolayer step‐flow growth without 2‐D islands and terraces about 1 μm wide are obtained above 630 °C for all materials. These results are very different from those by molecular beam epitaxy and suggest that MOVPE is superior to grow wide uniform heterointerfaces for GaAs/AlAs and GaAs/AlGaAs.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology

Highly uniform InGaAs/GaAs quantum dots (∼15 nm) by metalorganic chemical vapor deposition

J. Oshinowo, M. Nishioka, S. Ishida, and Y. Arakawa

Appl. Phys. Lett. 65, 1421 (1994); http://dx.doi.org/10.1063/1.112070 (3 pages) | Cited 96 times

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We report the direct deposition of strained InGaAs‐dot structures with a diameter of about 15 nm on GaAs surfaces by metalorganic chemical vapor deposition growth. High resolution scanning electron micrographs show highly uniform quantum‐sized dots formed by the Stranski–Krastanow growth mode. The sharp photoluminescence emission band of buried dot structures indicates efficient carrier capture and a homogeneous heterointerface. The average dot size and area dot density can be controlled accurately by growth temperature, and InGaAs deposition thickness, respectively.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
78.55.Cr III-V semiconductors

Anisotropic structural, electronic, and optical properties of InGaAs grown by molecular beam epitaxy on misoriented substrates

R. S. Goldman, H. H. Wieder, K. L. Kavanagh, K. Rammohan, and D. H. Rich

Appl. Phys. Lett. 65, 1424 (1994); http://dx.doi.org/10.1063/1.112071 (3 pages) | Cited 10 times

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We have investigated the structural, electronic, and optical properties of partially strain‐relaxed InxGa1−xAs layers, grown by molecular beam epitaxy on both misoriented and nominally flat (001) GaAs substrates. We find large anisotropies in bulk strain relaxation, interfacial misfit dislocation density, dark‐line defect density, and electron mobility, as well as a polarization anisotropy in cathodoluminescence for epilayers grown on misoriented substrates, in comparison with those grown on flat substrates.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology

Characterization of Ca+ ion‐implanted GaAs by photoluminescence

Hong‐Lie Shen, Yunosuke Makita, Shinji Kimura, Hisao Tanoue, Akimasa Yamada, Hajime Shibata, Akira Obara, and Shiro Sakuragi

Appl. Phys. Lett. 65, 1427 (1994); http://dx.doi.org/10.1063/1.112005 (3 pages) | Cited 5 times

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Optical properties of Ca+ ion‐implanted GaAs were characterized by photoluminescence measurements at 2 K. Four new emissions denoted by (Ca0,X), gCa, SM, and (e,Ca) were found to be produced by Ca incorporation into GaAs. By changing the Ca dopant concentration and excitation intensity, it was revealed that the (Ca0, X) emission is due to excitons bound to a neutral shallow Ca acceptor, and SM probably originates from excitons bound to a Ca impurity in a deep energy level. In addition, in an impure GaAs substrate, Ca could also form a shallow emission gCa, despite the fact that the g emission for well‐known shallow acceptors such as C, Be, and Mg was usually found only in ultrapure GaAs. It was demonstrated that Ca is a shallow acceptor impurity in GaAs with a binding energy of 28.4 meV.
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78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors

Photoluminescence, intersubband absorption, and double crystal x‐ray diffraction in p‐doped InGaAs/AlGaAs strained multiple quantum wells

V. W. L. Chin, T. L. Tansley, D. H. Zhang, K. Radhakrishnan, S. F. Yoon, and A. Clark

Appl. Phys. Lett. 65, 1430 (1994); http://dx.doi.org/10.1063/1.112006 (3 pages) | Cited 2 times

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We report the correlation of photoluminescence (PL), infrared intersubband absorption, and double crystal x‐ray diffraction (DCXRD) data for a p‐doped InGaAs/AlGaAs strained multi‐ ple‐quantum‐well structure grown by molecular beam epitaxy. A PL doublet at 1.476 and 1.563 eV involves two confined holes states and their 87 meV separation is in good agreement with the measured intersubband absorption of about 14.5 μm (85 meV). Furthermore, when the well width obtained from DCXRD measurement is included excellent agreement with an envelope function calculation is found for the energy levels determined by PL and intersubband absorption energy.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Hall measurements on selectively doped InSb heterostructures grown by molecular beam epitaxy on GaAs (001)

P. Songpongs, T. G. Andersson, M. J. Ekenstedt, J. R. Söderström, and M. M. Cumming

Appl. Phys. Lett. 65, 1433 (1994); http://dx.doi.org/10.1063/1.112007 (3 pages) | Cited 5 times

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Hall measurements were made on selectively Si‐doped InSb, GaSb/InSb, and GaAs/InSb heterostructures grown by molecular beam epitaxy using cracker sources. A cap layer had a pronounced influence especially on the low temperature conduction. The measurements showed an apparent increase in free carrier concentration and reduction of mobility due to compensation and/or parallel conduction. The best mobility, 38 700 cm2/V s at room temperature, was measured in a 2‐μm‐thick InSb layer capped with GaSb and doped with a concentration of 3×1016 cm−3 within 1000 Å from the cap interface. The variation of carrier concentration with temperature in doped samples revealed singularities at 50 and 90 K due to conduction from an unintentional p‐background doping.
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73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Evidence that blue luminescence of oxidized porous silicon originates from SiO2

A. J. Kontkiewicz, A. M. Kontkiewicz, J. Siejka, S. Sen, G. Nowak, A. M. Hoff, P. Sakthivel, K. Ahmed, P. Mukherjee, S. Witanachchi, and J. Lagowski

Appl. Phys. Lett. 65, 1436 (1994); http://dx.doi.org/10.1063/1.112973 (3 pages) | Cited 92 times

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We have analyzed red and blue luminescence from porous silicon as a function of oxidation parameters and feature dimension determined with an atomic force microscope. We have found correlation between blue luminescence intensity and the increase in feature size caused by oxidation. We have further shown that blue luminescence, is identical, with respect to spectrum and fast decay, to that of high microelectronic quality SiO2 grown on crystalline silicon using dry oxygen plus an organic chlorine compound. Thus, we conclude that blue luminescence originates from SiO2 film rather than from the silicon nanocrystals in the porous material. Intensity enhancement, as compared to SiO2 on crystalline wafers, comes from the gigantic surface area of porous silicon.
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78.55.Hx Other solid inorganic materials
81.65.-b Surface treatments

Growth of β‐FeSi2 on Si(111) by chemical beam epitaxy

J. Y. Natoli, I. Berbezier, and J. Derrien

Appl. Phys. Lett. 65, 1439 (1994); http://dx.doi.org/10.1063/1.112008 (3 pages) | Cited 7 times

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The growth of high quality semiconducting β‐FeSi2 layers on silicon substrates is rather difficult due to a large lattice mismatch [up to ∼5.5% on Si(111)] and very different crystallographic structure (orthorhombic structure on top of the diamond one). We report on a new method using the chemical beam epitaxy (CBE) technique to stabilize at first the tetragonal α‐FeSi2 phase (lattice mismatch ∼0.8% on Si(111)) at ∼550 °C. Then a post‐annealing up to ∼650 °C induces a phase transition from the α to β phase via a tremendous coalescence of numerous small metallic α grains (∼200 Å width) into large semiconducting β‐grains (≤1 μm width) of high quality, suitable for Si integrated optoelectronic technology.
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68.55.-a Thin film structure and morphology

Direct measurements of lattice parameter variations and relaxation kinetics in strained Si1−xGex/Si heterostructures

M. R. Sardela and G. V. Hansson

Appl. Phys. Lett. 65, 1442 (1994); http://dx.doi.org/10.1063/1.112009 (3 pages) | Cited 4 times

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Lattice parameter variations in strained Si1−xGex/Ge (x<0.23) induced by high‐temperature annealing in the range 700–1000 °C, were determined by x‐ray high‐resolution reciprocal lattice mapping of the crystal structure. In the range 700–800 °C, the strain relaxation was found to increase by one order of magnitude owing to glide propagation of misfit dislocations, with an activation energy of 2.3 eV. In the range 850–1000 °C, relaxation was still high but the increase with the temperature was limited by dislocation interactions.
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68.55.-a Thin film structure and morphology
68.60.Dv Thermal stability; thermal effects
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Large‐amplitude Shapiro steps and self‐field effects in high‐Tc Josephson weak links

R. L. Kautz, S. P. Benz, and C. D. Reintsema

Appl. Phys. Lett. 65, 1445 (1994); http://dx.doi.org/10.1063/1.112010 (3 pages) | Cited 16 times

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We demonstrate contiguous Shapiro steps of orders 0 and 1 having amplitudes of 1 mA in a YBa2Cu3O7−δ step‐edge junction operated at 38 K. A wide‐junction model that includes self‐field effects explains why the observed step amplitudes are smaller than expected from the resistively shunted point‐junction model. In spite of their reduced amplitudes, the observed steps are suitable for use in a proposed rapidly programmable Josephson voltage standard.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
06.20.F- Units and standards

Enhanced critical currents by CeO2 additions in directionally solidified YBa2Cu3O7

S. Piñol, F. Sandiumenge, B. Martínez, V. Gomis, J. Fontcuberta, X. Obradors, E. Snoeck, and Ch. Roucau

Appl. Phys. Lett. 65, 1448 (1994); http://dx.doi.org/10.1063/1.112011 (3 pages) | Cited 70 times

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The microstructure and critical currents of superconducting YBa2Cu3O7‐Y2BaCuO5 composites with small CeO2 additions prepared using a directional solidification procedure have been investigated. The small CeO2 additions cause the decomposition of the Y2BaCuO5 phase leading to the formation of Y2O3 and BaCeO3. Experimental evidence is given for the subsequent nucleation of the Y2BaCuO5 phase on the Y2O3 particles. This new decomposition‐nucleation mechanism leads to textured YBa2Cu3O7 having enhanced critical currents. An addition of 0.3 wt % CeO2 can increase Jabc by a factor of 2 in samples having similar concentration of Y2BaCuO5 precipitates. Critical currents above 105 A/cm2 at 77 K and zero field are obtained by this method.
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74.25.Sv Critical currents
74.72.-h Cuprate superconductors
81.30.Mh Solid-phase precipitation

Preparation of epitaxial TlBa2Ca2Cu3O9 high Tc thin films on LaAlO3 (100) substrates

A. Piehler, N. Reschauer, U. Spreitzer, J. P. Ströbel, R. Schönberger, K. F. Renk, and G. Saemann‐Ischenko

Appl. Phys. Lett. 65, 1451 (1994); http://dx.doi.org/10.1063/1.112012 (3 pages) | Cited 3 times

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Epitaxial TlBa2Ca2Cu3O9 high Tc thin films were prepared on LaAlO3 (100) substrates by a combination of laser ablation and thermal evaporation of thallium oxide. X‐ray diffraction patterns of θ‐2θ scans showed that the films consisted of highly c axis oriented TlBa2Ca2Cu3O9. ϕ scan measurements revealed an epitaxial growth of the TlBa2Ca2Cu3O9 thin films on the LaAlO3 (100) substrates. Ac inductive measurements indicated the onset of superconductivity at 110 K. At 6 K, the critical current density was 4×106 A/cm2 in zero magnetic field and 6×105 A/cm2 at a magnetic field of 3 T parallel to the c axis.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
68.55.-a Thin film structure and morphology

Strain tolerance of multifilament Bi‐Pb‐Sr‐Ca‐Cu‐O/silver composite superconducting tapes

John Yau and Nick Savvides

Appl. Phys. Lett. 65, 1454 (1994); http://dx.doi.org/10.1063/1.112013 (3 pages) | Cited 24 times

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The bend strain characteristics of Bi‐Pb‐Sr‐Ca‐Cu‐O/silver composite tapes were determined from measurements of the critical current, Ic(77 K), as a function of bend strain (0%–2%) or radius of curvature (∞−10 mm). The powder‐in‐tube method was used to prepare monofilament and multifilament (up to 49 filaments) tapes, 0.2–0.4 mm overall thickness, with 5–20 vol % superconductor. The irreversible strain limit, ϵirr, for the onset of bend strain damage, increases with the number of filaments from ϵirr=0.2%–0.3% for monofilament tapes to values up to 1.5% for 49‐filament tapes. Although strains beyond this limit cause irreversible damage in the form of microcracks and fracture of the superconductor filaments, multifilament tapes are exceptionally strain tolerant, with 49‐filament tapes retaining 85%–90% of the initial critical current at strains of 2%.
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84.71.Mn Superconducting wires, fibers, and tapes
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.40.Lm Deformation, plasticity, and creep
74.25.Sv Critical currents

Possible phase locking of vertically stacked Josephson flux‐flow oscillators

A. V. Ustinov, H. Kohlstedt, and C. Heiden

Appl. Phys. Lett. 65, 1457 (1994); http://dx.doi.org/10.1063/1.112014 (3 pages) | Cited 37 times

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A system of two vertically stacked Nb/Al‐AlOx/Nb long Josephson junctions is studied experimentally. The magnetic coupling between the junctions is provided by their common electrode of the thickness d∼λL. The current‐voltage characteristics of the stack displays resonant steps which are understood to be the phase‐locked flux‐flow resonances of the two junctions. These modes can be tuned by the magnetic field in a broad voltage range which corresponds to the Josephson frequencies between 150 and 600 GHz. Our observations suggest a possibility of application of the stacked long Josephson junctions as local oscillators for millimeter and submillimeter wave circuits.
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85.25.Cp Josephson devices
74.50.+r Tunneling phenomena; Josephson effects
74.78.Fk Multilayers, superlattices, heterostructures

Spin coupled resistance observed in ferromagnet‐superconductor‐ferromagnet trilayers

Mark Johnson

Appl. Phys. Lett. 65, 1460 (1994); http://dx.doi.org/10.1063/1.112015 (3 pages) | Cited 55 times

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Permalloy‐niobium‐permalloy trilayers are fabricated in the spin transistor geometry, and the results of transport measurements above and below the superconducting transition temperature Tc are reported. The data below Tc show evidence for the injection of nonequilibrium, spin‐polarized quasiparticles, and their diffusion across the niobium film.
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73.40.-c Electronic transport in interface structures
74.78.Fk Multilayers, superlattices, heterostructures
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Preparation of La‐modified PbTiO3 thin films on the oxide buffer layers with NaCl‐type structure

Satoru Fujii, Atsushi Tomozawa, Eiji Fujii, Hideo Torii, Ryoichi Takayama, and Takashi Hirao

Appl. Phys. Lett. 65, 1463 (1994); http://dx.doi.org/10.1063/1.112016 (3 pages) | Cited 13 times

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La‐modified PbTiO3(PLT: Pb0.9La0.1Ti0.975O3) thin films by rf magnetron sputtering were prepared on the preferred (100)‐oriented oxide buffer layers with NaCl‐type structure, which were prepared by plasma‐enhanced metalorganic chemical vapor deposition. Fused silica, (111)Si, soda‐lime glass, and stainless steel were used as the substrates to prepare the oxide buffer layers. The c‐axis and a‐axis preferred oriented PLT thin films were obtained on the buffer layer, independent of the kind of substrate. Further, highly c‐axis oriented PLT thin films were obtained when the substrate had a large thermal expansion coefficient. Significant pyroelectric currents were detected without a poling treatment. The NiCr/PLT/(100)Pt/(100)MgO/stainless steel structure had a dielectric constant of 250, a dielectric loss factor tan δ of 0.8%, and a pyroelectric coefficient of 3.8×10−4 C/m2 K.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.55.-g Dielectric thin films

Design of three‐dimensional photonic crystals at submicron lengthscales

Shanhui Fan, Pierre R. Villeneuve, Robert D. Meade, and J. D. Joannopoulos

Appl. Phys. Lett. 65, 1466 (1994); http://dx.doi.org/10.1063/1.112017 (3 pages) | Cited 68 times

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We present a new class of periodic dielectric structures designed specifically to be amenable for fabrication at submicron lengthscales. The structures give rise to a sizable 3D photonic band gap and can be fabricated with materials widely used today in optoelectronic devices. They are made of three materials and consist essentially of a layered structure in which a series of cylindrical air holes are etched at normal incidence through the top surface of the structure. Our results demonstrate the existence of a gap as large as 14% of the midgap frequency using Si, SiO2, and air; and 23% using Si and air.
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42.90.+m Other topics in optics (restricted to new topics in section 42)
42.82.Cr Fabrication techniques; lithography, pattern transfer
68.55.-a Thin film structure and morphology
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