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8 Jul 2002

Volume 81, Issue 2, pp. 187-387

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Wide bandwidth, large, and tunable polarization mode dispersions in multilayered omnidirectional reflectors

Zheng Wang, David A. B. Miller, and Shanhui Fan

Appl. Phys. Lett. 81, 187 (2002); http://dx.doi.org/10.1063/1.1491284 (3 pages) | Cited 3 times

Online Publication Date: 27 June 2002

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We numerically demonstrate the generation of large, broadband, and tunable polarization mode dispersion (PMD) with omnidirectionally reflecting dielectric stacks with embedded cavities. Both first-order and second-order polarization mode dispersion can be generated by similar configurations. Our examples show that the first-order PMD can be tuned from 0 to 30 ps over an 80 GHz bandwidth and second-order PMD from 0 to 50 ps/nm can be generated over a 100 GHz bandwidth. We also show that in our configuration there is no significant modal distortion of the light beams when the beam diameters exceed 3.5 mm. © 2002 American Institute of Physics.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Charge carrier mobility and photorefractive grating buildup in bipolar organic glasses

Jiwon Sohn, Jaehoon Hwang, Soo Young Park, Yong-Young Noh, and Jang-Joo Kim

Appl. Phys. Lett. 81, 190 (2002); http://dx.doi.org/10.1063/1.1492312 (3 pages) | Cited 2 times

Online Publication Date: 27 June 2002

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Two-component organic glasses consisting of photoconductive molecule, N′-[9-(2-ethylhexyl)-9H-carbazol-3-ylmethylene]-N,N-diphenyl-hydrazine (EHCzHy), and multifunctional photorefractive molecules, 9-(2-ethyl-hexyl)-3-[2-(4-methanesulfonyl-phenyl)-vinyl]-9H-carbazole (EHCS) [J. Sohn et al., Appl. Phys. Lett. 77, 1422 (2000)] and 9-(2-ethylhexyl)-3-[2-(4-nitro-phenyl)-vinyl]-9H-carbazole (EHCN), were prepared, and their charge carrier mobility and photorefractive grating buildup were investigated. EHCzHy is a unipolar hole-transporting (μh = 4.16×10−6 cm2/V s) molecule with no electro-optic property. EHCS and EHCN are nonlinear optical molecules with unipolar (μh = 2.42×10−6 cm2/V s) and bipolar (μh = 2.30×10−6 cm2/V s,μe = 2.86×10−6 cm2/V s) carrier mobilities, respectively. Different behaviors of the photorefractive grating buildup in two-component organic glasses were investigated as a function of EHCN or EHCS content. © 2002 American Institute of Physics.
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42.70.Ce Glasses, quartz
42.70.Gi Light-sensitive materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
72.80.Le Polymers; organic compounds (including organic semiconductors)
72.20.Fr Low-field transport and mobility; piezoresistance
72.40.+w Photoconduction and photovoltaic effects
42.65.-k Nonlinear optics

Detection of nonresonant impurity gases in alkali vapor cells

I. Novikova, A. B. Matsko, and G. R. Welch

Appl. Phys. Lett. 81, 193 (2002); http://dx.doi.org/10.1063/1.1492309 (3 pages) | Cited 3 times

Online Publication Date: 27 June 2002

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We show that even small amounts of impurity gases significantly change the properties of the nonlinear Faraday effect in alkali vapor cells. These changes result from velocity-changing collisions. We propose a simple method of detection and measurement of the impurities based on this effect. © 2002 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
32.60.+i Zeeman and Stark effects
42.65.-k Nonlinear optics

Embedded anisotropic microreflectors by femtosecond-laser nanomachining

John D. Mills, Peter G. Kazansky, Erica Bricchi, and Jeremy J. Baumberg

Appl. Phys. Lett. 81, 196 (2002); http://dx.doi.org/10.1063/1.1492004 (3 pages) | Cited 30 times

Online Publication Date: 27 June 2002

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Directly written embedded structures created within fused silica by a femtosecond Ti:sapphire laser are observed to strongly reflect blue light. Reflection emerges only in a direction parallel to the polarization axis of the writing laser. This anisotropic-effect is caused by a periodic modulation of refractive index of amplitude Δn ∼ 10−2 with a characteristic period Λ ∼ 150 nm over a spot size ∼1.5 μm. We show that the origin of the anisotropic reflection is the primary cause of other anisotropic phenomena reported in recent experiments. © 2002 American Institute of Physics.
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42.79.Fm Reflectors, beam splitters, and deflectors
81.65.Cf Surface cleaning, etching, patterning
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Terahertz frequency Hall measurement by magneto-optical Kerr spectroscopy in InAs

R. Shimano, Y. Ino, Yu. P. Svirko, and M. Kuwata-Gonokami

Appl. Phys. Lett. 81, 199 (2002); http://dx.doi.org/10.1063/1.1492319 (3 pages) | Cited 26 times

Online Publication Date: 27 June 2002

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We report on the time-domain terahertz (THz) magneto-optical Kerr spectroscopy in the frequency range from 0.5 to 2.5 THz. The developed technique employs reflection geometry, enabling high-frequency noncontact Hall measurements in opaque samples. We also present a method to reveal the off-diagonal component of the complex dielectric tensor from the measured polarization-dependent THz wave forms. At a static magnetic field of 0.48 T, a large Kerr rotation over 10° originating from magnetoplasma resonance is observed in an n-type undoped InAs wafer at room temperature. This indicates the strong potential of this material for the polarization modulator in the THz regime. © 2002 American Institute of Physics.
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78.20.Ls Magneto-optical effects
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.30.Fs III-V and II-VI semiconductors

Dynamic tuning of optical waveguides with electrowetting pumps and recirculating fluid channels

P. Mach, T. Krupenkin, S. Yang, and J. A. Rogers

Appl. Phys. Lett. 81, 202 (2002); http://dx.doi.org/10.1063/1.1491608 (3 pages) | Cited 39 times

Online Publication Date: 27 June 2002

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We have developed an approach for using electrowetting actuation in recirculating fluidic channels to achieve dynamic tuning of optical fiber structures. The electrically controlled and fully reversible motion of the fluids and lubricants in these channels alters the refractive index profile experienced by the optical waveguide modes of the fiber. When combined with in-fiber gratings and etched fibers, this fluidic system yields dynamically adjustable narrow and broadband fiber filters, respectively. The nonmechanical operation of these systems, their ability to support switching speeds on the order of milliseconds, and their excellent optical characteristics indicate a promising potential for electrowetting-actuated fluidic tuning in optical fiber devices and other photonic components. © 2002 American Institute of Physics.
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42.81.Ht Gradient-index (GRIN) fiber devices
42.79.Gn Optical waveguides and couplers
47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.85.Np Fluidics
42.79.Ci Filters, zone plates, and polarizers
42.81.Wg Other fiber-optical devices
42.65.Wi Nonlinear waveguides
68.08.Bc Wetting
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Optoelectronic characteristics of polymer light emitting diodes with poly(2-methoxy-5-(2′ethyl-hexoxy)-1,4-phenylene-vinylene) and hydrogenated amorphous silicon alloy heterointerfaces

Cha-Shin Lin, Rong-Hwei Yeh, Chih-Ping Huang, and Jyh-Wong Hong

Appl. Phys. Lett. 81, 205 (2002); http://dx.doi.org/10.1063/1.1492310 (3 pages) | Cited 1 time

Online Publication Date: 27 June 2002

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In order to investigate the feasibility of combining polymer and inorganic films for light-emitting diode (LED) fabrication, the inorganic p-amorphous-Si:H/n-amorphous-SiCGe:H layer was employed as hole/electron injection layer (HIL/EIL) in the poly(2-methoxy-5-(2′ ethylhexoxy)-1,4-phenylene-vinylene) polymer LEDs (PLEDs). In contrast to the PLED without any amorphous HIL/EIL, which had an electroluminescence (EL) threshold voltage (Vth) of 10 V and a brightness of 1231 cd/m2 at an injected current density (J) = 0.6 A/cm2, the EL Vth could be reduced to 6.9 V for PLED with a 6 nm p-a-Si:H HIL only, also, the brightness could be enhanced to 6450 cd/m2 (at J = 0.3 A/cm2 only) for PLED with both p-amorphous-Si:H HIL and n-a-SiCGe:H EIL. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.05.Gc Amorphous semiconductors
61.41.+e Polymers, elastomers, and plastics
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
61.43.Dq Amorphous semiconductors, metals, and alloys
73.61.Jc Amorphous semiconductors; glasses
78.66.Jg Amorphous semiconductors; glasses
68.55.-a Thin film structure and morphology

Midinfrared IV–VI vertical-cavity surface-emitting lasers with zero-, two-, and three-dimensional systems in the active regions

J. Fürst, H. Pascher, T. Schwarzl, M. Böberl, W. Heiss, G. Springholz, and G. Bauer

Appl. Phys. Lett. 81, 208 (2002); http://dx.doi.org/10.1063/1.1491285 (3 pages) | Cited 17 times

Online Publication Date: 27 June 2002

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A comparison between IV–VI vertical-cavity surface-emitting midinfrared lasers containing active regions of different dimensionality is presented. Optically pumped laser emission is observed at wavelengths between 3.5 and 4.4 μm. The microcavities consist of high-reflectivity EuTe/PbEuTe Bragg mirrors, with active regions consisting either of a self-organized PbSe/PbEuTe quantum-dot superlattice, PbTe/PbEuTe multiquantum wells, or bulk-like PbTe. For the zero dimensional active medium, laser emission is obtained at temperatures up to 150 K. The results for the lasers with two-dimensional active region are similar to those with the three-dimensional bulk-like active region, for which lasing is observed up to 317 K. The threshold pump intensity is only 4 kW/cm2 at 195 K, and 15.6 kW/cm2 at room temperature. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Dark decay of holograms in photorefractive polymers

Reinhard Bittner, Klaus Meerholz, Gregory Steckman, and Demetri Psaltis

Appl. Phys. Lett. 81, 211 (2002); http://dx.doi.org/10.1063/1.1492848 (3 pages) | Cited 6 times

Online Publication Date: 27 June 2002

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The decay of holograms stored in photorefractive polymer composites based on poly(N-vinyl-carbazole) with and without extrinsic deep traps is investigated. The photorefractive phase shift is identified as one of the key parameters determining the dark decay dynamics. This has important implications for all kinds of photorefractive imaging applications including holographic data storage. A trade off will be required between accepting a certain degree of hologram distortion due to two-beam coupling on the one hand and achieving high hologram stability during idle periods in the dark with the external field applied on the other. © 2002 American Institute of Physics.
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42.70.Gi Light-sensitive materials
42.70.Jk Polymers and organics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Ln Holographic recording materials; optical storage media
42.79.Vb Optical storage systems, optical disks
42.40.Ht Hologram recording and readout methods

High-efficiency polymer light-emitting devices using organic salts: A multilayer structure to improve light-emitting electrochemical cells

Tae-Woo Lee, Ho-Chul Lee, and O. Ok Park

Appl. Phys. Lett. 81, 214 (2002); http://dx.doi.org/10.1063/1.1490635 (3 pages) | Cited 21 times

Online Publication Date: 27 June 2002

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Balanced charge injection in polymer light-emitting devices is very important for high brightness and quantum efficiency. To improve the well-known light-emitting electrochemical cells (LECs), we fabricated multilayer electroluminescent devices employing an ammonium salt-containing poly(ethylene oxide) blend as hole- or electron-injecting materials. The charge injection can be greatly promoted due to the ionic space charges near both electrodes. The current–voltage–optical output characteristics of the triple-layer device using both the hole- and the electron-injecting layers are very similar to the well-known LEC devices. We obtained high quantum efficiencies of 0.9% and 1.5% photons/electron in forward- and reverse-bias field of the triple-layer device, respectively. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
82.47.-a Applied electrochemistry
73.61.Ph Polymers; organic compounds
78.60.Fi Electroluminescence
42.70.Jk Polymers and organics

Correlation between the gain profile and the temperature-induced shift in wavelength of quantum-dot lasers

F. Klopf, S. Deubert, J. P. Reithmaier, and A. Forchel

Appl. Phys. Lett. 81, 217 (2002); http://dx.doi.org/10.1063/1.1491612 (3 pages) | Cited 29 times

Online Publication Date: 27 June 2002

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The influence of several design parameters on the temperature stability of the emission wavelength of 980 nm GaInAs/(Al)GaAs quantum-dot lasers was studied. The results obtained agree well with a simplified model based on the inhomogeneously broadened transitions of a quantum-dot ensemble. Using this model, the optimum cavity design for a given gain function can be determined. Following this approach, quantum-dot lasers with low wavelength shifts of 0.16 nm/K were realized, which is only half the value of a typical GaInAs/(Al)GaAs quantum well laser. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Ultrafast spin dynamics in GaAs/GaSb/InAs heterostructures probed by second harmonic generation

Yu. D. Glinka, T. V. Shahbazyan, I. E. Perakis, N. H. Tolk, X. Liu, Y. Sasaki, and J. K. Furdyna

Appl. Phys. Lett. 81, 220 (2002); http://dx.doi.org/10.1063/1.1494107 (3 pages) | Cited 4 times

Online Publication Date: 27 June 2002

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We report the application of pump-probe second harmonic generation (SHG) to monitor spin dynamics in nonmagnetic semiconductor heterostructures. Spin-polarized electrons were selectively excited by a pump beam in the GaAs layer of GaAs/GaSb/InAs structures. However, the induced magnetization manifests itself through the SHG probe signal from the GaSb/InAs interface, thus indicating a spin-polarized electron transport. We find that the magnetization dynamics is governed by an interplay between the spin density evolution at the interfaces and the spin relaxation. © 2002 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Dc Spin polarized transport in semiconductors
72.25.Fe Optical creation of spin polarized carriers
72.25.Mk Spin transport through interfaces
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
72.25.Rb Spin relaxation and scattering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Optical second order nonlinearity of transparent Ba2TiGe2O8 crystallized glasses

Yoshihiro Takahashi, Yasuhiko Benino, Takumi Fujiwara, and Takayuki Komatsu

Appl. Phys. Lett. 81, 223 (2002); http://dx.doi.org/10.1063/1.1493667 (3 pages) | Cited 37 times

Online Publication Date: 27 June 2002

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Optical second-order nonlinearity of ferroelastic Ba2TiGe2O8 crystal in transparent crystallized glasses was estimated by means of the Maker fringe technique. Transparent crystallized glasses were fabricated by crystallization of a glass with the composition of 30 BaO.15 TiO2.55 GeO2. The crystalline layer consisting of highly oriented Ba2TiGe2O8 crystals was formed at the surface of about 9 μm thickness, and a clear second-harmonic generation was observed. The optical second-order nonlinearity of d33 for Ba2TiGe2O8 crystal was found to be ∼ 10 pm/V, being comparable to d22 and d31 of LiNbO3, and demonstrating that Ba2TiGe2O8 crystal is an excellent candidate for nonlinear optical crystals. © 2002 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
81.05.Kf Glasses (including metallic glasses)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
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Picosecond pulse frequency upshifting by rapid free-carrier creation in ZnSe

I. Geltner, Y. Avitzour, and S. Suckewer

Appl. Phys. Lett. 81, 226 (2002); http://dx.doi.org/10.1063/1.1491290 (3 pages) | Cited 8 times

Online Publication Date: 27 June 2002

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The frequency upshifting of 0.8 μm picosecond laser pulses was demonstrated using the temporal change of the free carrier density in a ZnSe semiconductor crystal. The crystal was ionized by transverse propagating ps pulses. Shifts of up to 1.6 nm were observed, which agree within 25% with the theory. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.47.-p Spectroscopy of solid state dynamics
78.55.Et II-VI semiconductors
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Structure and bonding in a cubic phase of SiAlON derived from the cubic spinel phase of Si3N4

Lizhi Ouyang and W. Y. Ching

Appl. Phys. Lett. 81, 229 (2002); http://dx.doi.org/10.1063/1.1491004 (3 pages) | Cited 11 times

Online Publication Date: 27 June 2002

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The structure and electronic bonding in the spinel SiAlON (Si6−zAlzOzN8−z, z = 1) derived from the cubic c-Si3N4 are studied by a first-principles density functional method. Al prefers the octahedral site of the spinel lattice. The small energy difference between the four possible structural configurations indicates that the real SiAlON may be a random solid solution. The lowest energy configuration of c-Si5AlON7 is a semiconductor with a direct LDA band gap of 2.29 eV. © 2002 American Institute of Physics.
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61.66.Fn Inorganic compounds
61.50.Lt Crystal binding; cohesive energy
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Nr Semiconductor compounds
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
71.15.-m Methods of electronic structure calculations

Different pressure coefficients of the light emission in cubic and hexagonal InGaN/GaN quantum wells

T. Suski, H. Teisseyre, S. P. Łepkowski, P. Perlin, T. Kitamura, Y. Ishida, H. Okumura, and S. F. Chichibu

Appl. Phys. Lett. 81, 232 (2002); http://dx.doi.org/10.1063/1.1490400 (3 pages) | Cited 6 times

Online Publication Date: 27 June 2002

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We have studied the influence of hydrostatic pressure on the light emission from cubic In0.1Ga0.9N. A qualitative difference between pressure dependence of photoluminescence peak energies for cubic and wurtzite symmetry InGaN/GaN quantum wells (QWs) was found. Cubic samples revealed magnitude of dEE/dP of 26–30 meV/GPa, practically independent of the QW width. Previous studies of the hexagonal InGaN/GaN structures showed that with increasing QW width dEE/dP changed between about 30 meV/GPa and 0 meV/GPa. This different behavior of two types of QWs can be explained by the lack of built-in electric field (along growth direction) in case of cubic structures. To describe pressure evolution of the optical transitions in cubic InGaN/GaN QWs and thick epitaxial layer, we use a simple k×p model based on the linear theory of elasticity. To reproduce the experimental data, it is necessary to invoke presence of In-rich fluctuations in the cubic In0.1Ga0.9N samples. © 2002 American Institute of Physics.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.40.Fy Semiconductors

Systematic examination of carrier polarity in composition spread ZnO thin films codoped with Ga and N

A. Tsukazaki, H. Saito, K. Tamura, M. Ohtani, H. Koinuma, M. Sumiya, S. Fuke, T. Fukumura, and M. Kawasaki

Appl. Phys. Lett. 81, 235 (2002); http://dx.doi.org/10.1063/1.1491294 (3 pages) | Cited 55 times

Online Publication Date: 27 June 2002

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We have grown high-crystallinity ZnO thin films on lattice-matched ScAlMgO4 substrates by pulsed-laser deposition with doping donor (Ga) and acceptor (N) simultaneously. Alternating ablation of ceramics with concentrated Ga addition and highly pure single crystal targets yielded in a controlled Ga concentration (CGa) in a wide range of 1018–1020 cm−3 with minimal contamination of undesired impurities such as Al and Si. The use of the originally developed temperature-gradient method, where controlled and continuous gradient of the growth temperature is given to the single substrate with a range of about 50–200 °C, results in a continuous spread of N concentration (CN) in a controlled fashion. Therefore, the ratio of CN/CGa can be varied continuously in a wide range for each film, assuring that a region satisfying p-type codoping condition predicted by T. Yamamoto and H. K. Yoshida [Jpn. J. Appl. Phys., Part 2 38, L166 (1999)] is included in the sample. The electrical properties were measured for over thousand specimens of lithographically patterned Hall bars without observing any sign of p-type conduction. © 2002 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.05.Dz II-VI semiconductors
73.61.Ga II-VI semiconductors
71.55.Gs II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Fg Pulsed laser ablation deposition
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

(Zr,Ti)O2 interface structure in ZrO2–TiO2 nanolaminates with ultrathin periodicity

C. R. Aita, J. D. DeLoach, and V. V. Yakovlev

Appl. Phys. Lett. 81, 238 (2002); http://dx.doi.org/10.1063/1.1492013 (3 pages) | Cited 11 times

Online Publication Date: 27 June 2002

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A mixed cation interfacial structure in ZrO2–TiO2 nanolaminate films with ultrathin bilayer periodicity grown by sputter deposition at 297 K was identified by x-ray diffraction and nonresonant Raman spectroscopy. This structure consists of an amorphous phase at a ZrO2-on-TiO2 bilayer interface, followed by an extensive crystalline monoclinic (Zr,Ti)O2 solid solution predicted by Vegard’s law. Monoclinic (Zr,Ti)O2 has previously been reported only once, in bulk powder of a single composition (ZrTiO4) at high pressure. Its stabilization in the nanolaminates is explained by the Gibbs–Thomson effect. This complex interfacial structure is shown to be a means of accommodating chemical mixing in the absence of a driving force for heteroepitaxy. © 2002 American Institute of Physics.
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68.35.Ct Interface structure and roughness
81.15.Cd Deposition by sputtering
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators

From nucleation to coalescence of Cu2O islands during in situ oxidation of Cu(001)

J. C. Yang, D. Evan, and L. Tropia

Appl. Phys. Lett. 81, 241 (2002); http://dx.doi.org/10.1063/1.1492007 (3 pages) | Cited 21 times

Online Publication Date: 27 June 2002

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The nucleation, growth, and coalescence of Cu2O islands due to oxidation of Cu(001) films were visualized by in situ ultrahigh-vacuum transmission electron microscopy. We have previously demonstrated that the nucleation and initial growth of copper oxides is dominated by oxygen surface diffusion. These surface models have been extended to quantitatively represent the coalescence behavior of copper oxidation in the framework of the Johnson–Mehl–Avrami–Kolmogorov theory. An excellent agreement exists between the experimental data of nucleation to coalescence with the surface model. The implication could be an alternate paradigm for passivation and oxidation, since classic theories assume uniform film growth. © 2002 American Institute of Physics.
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81.05.Bx Metals, semimetals, and alloys
81.65.Mq Oxidation
68.35.Fx Diffusion; interface formation

Evidence of noble metal diffusion in polymers at room temperature and its retardation by a chromium barrier

A. Thran, T. Strunskus, V. Zaporojtchenko, and F. Faupel

Appl. Phys. Lett. 81, 244 (2002); http://dx.doi.org/10.1063/1.1491609 (3 pages) | Cited 11 times

Online Publication Date: 27 June 2002

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Recent applications of organic low-k dielectrics in microelectronics have stimulated many investigations of metal diffusion in polymers. Here we report results from radiotracer measurements of 110mAg diffusion in trimethylcyclohexane polycarbonate. Serial sectioning was carried out with 190 eV krypton ions in and opposite to the diffusion direction to rule out sputtering artifacts. Ag was found to be strongly immobilized by self aggregation. In contrast to earlier reports, however, trace amounts of Ag were clearly seen to diffuse into the polymer even at room temperature. A chromium film of only one tenth of a monolayer turned out to be an effective diffusion barrier. © 2002 American Institute of Physics.
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68.60.Wm Other nonelectronic physical properties
61.41.+e Polymers, elastomers, and plastics
66.30.J- Diffusion of impurities
68.35.Fx Diffusion; interface formation

Phase-sensitive second-harmonic microscopy reveals polarity of topologically centrosymmetric molecular crystals

S. Kluge, F. Budde, I. Dohnke, P. Rechsteiner, and J. Hulliger

Appl. Phys. Lett. 81, 247 (2002); http://dx.doi.org/10.1063/1.1492850 (3 pages) | Cited 11 times

Online Publication Date: 27 June 2002

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Phase-sensitive second-harmonic microscopy is applied to reveal grow-in polarity in topologically centrosymmetric crystals of 4-chloro-4′-nitrostilben. As predicted by the Markow model of layer-by-layer polarity formation, growth along + and −b-direction in P21/c is producing optical nonlinearity in both sectors associated with the b axis. Present experiments show that formation of a pyroelectric symmetry class is a stochastic property of molecular crystals grown from dipolar compounds and near to thermodynamic equilibrium. © 2002 American Institute of Physics.
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77.70.+a Pyroelectric and electrocaloric effects
61.66.Hq Organic compounds
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Optical properties of gallium oxide thin films

M. Rebien, W. Henrion, M. Hong, J. P. Mannaerts, and M. Fleischer

Appl. Phys. Lett. 81, 250 (2002); http://dx.doi.org/10.1063/1.1491613 (3 pages) | Cited 42 times

Online Publication Date: 27 June 2002

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The optical functions of β-Ga2O3 thin films have been determined by ellipsometry from 0.74–5 eV. Several electron-beam evaporated and rf magnetron sputtered films of different thicknesses were investigated using a multisample technique. Refractive index values comparable to those of bulk material are found. Cauchy dispersion model fits yield a high-frequency dielectric constant ϵ∞ of 3.57. Above 4.7 eV a direct absorption edge is observed. © 2002 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Nk Insulators

Visible photoluminescence in amorphous ABO3 perovskites

P. S. Pizani, H. C. Basso, F. Lanciotti, T. M. Boschi, F. M. Pontes, E. Longo, and E. R. Leite

Appl. Phys. Lett. 81, 253 (2002); http://dx.doi.org/10.1063/1.1494464 (3 pages) | Cited 21 times

Online Publication Date: 27 June 2002

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The photoluminescence observed in ABO3 type perovskite in their highly structural disordered state can be explained by a model in which is assumed a distribution of electronic states localized within the energy band gap coupled to lattice local vibrational states. The model fits very well the experimental results and indicates that photoluminescence in the visible region can be considered as a general behavior of disordered solids. © 2002 American Institute of Physics.
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78.55.-m Photoluminescence, properties and materials
71.55.Jv Disordered structures; amorphous and glassy solids
63.50.-x Vibrational states in disordered systems

Band anticrossing in dilute InNxSb1−x

B. N. Murdin, A. R. Adams, P. Murzyn, C. R. Pidgeon, I. V. Bradley, J.-P. R. Wells, Y. H. Matsuda, N. Miura, T. Burke, and A. D. Johnson

Appl. Phys. Lett. 81, 256 (2002); http://dx.doi.org/10.1063/1.1493663 (3 pages) | Cited 24 times

Online Publication Date: 27 June 2002

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Dilute nitrogen alloys of InSb exhibit extremely strong band gap bowing with nitrogen composition that has been associated with anticrossing between the localized resonant states of the nitrogen within the conduction band and the extended states of the conduction band itself. This also results in the conduction band dispersion having an enhanced nonparabolicity. We have measured the electron effective mass near the anticrossing by cyclotron resonance in InNxSb1−x alloys with absorption edge near 15 μm, using pulsed fields up to 150 T. The results directly demonstrate the band anticrossing and quantitatively confirm the increase of effective mass versus x predicted for InNxSb1−x by a tight binding calculation for low nitrogen concentration (x<0.01). © 2002 American Institute of Physics.
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71.20.Nr Semiconductor compounds
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
76.40.+b Diamagnetic and cyclotron resonances
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
78.20.Ls Magneto-optical effects
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Low resistivity TiSi2 on narrow p+ polycrystalline silicon lines

S. B. Herner and M. A. Vyvoda

Appl. Phys. Lett. 81, 259 (2002); http://dx.doi.org/10.1063/1.1492010 (3 pages) | Cited 3 times

Online Publication Date: 27 June 2002

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We have achieved low resistivity TiSi2 on 0.25 μm wide polysilicon lines doped to 5×1020/cm3 with boron by use of in situ doping of polysilicon. By controlling the Si deposition such that an amorphous undoped “cap” was deposited on p+ polycrystalline Si (polysilicon) subsequently formed TiSi2 wires had a lower resistivity consistent with C54 phase formation, while maintaining direct contact between TiSi2 and p+ Si. When TiSi2 was formed directly on p+ polysilicon, it had increasing resistivity as the linewidth decreased below 0.5 μm. The mechanism for lower resistivity TiSi2 is attributed to an increased density of C49-to-C54 phase transformation sites when the silicide is formed on amorphous undoped silicon. © 2002 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology
73.40.Cg Contact resistance, contact potential
64.70.K- Solid-solid transitions
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