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1 Oct 2001

Volume 79, Issue 14, pp. 2127-2296

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Phase transition-governed opal–VO2 photonic crystal

V. G. Golubev, V. Yu. Davydov, N. F. Kartenko, D. A. Kurdyukov, A. V. Medvedev, A. B. Pevtsov, A. V. Scherbakov, and E. B. Shadrin

Appl. Phys. Lett. 79, 2127 (2001); http://dx.doi.org/10.1063/1.1406144 (3 pages) | Cited 34 times

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Three-dimensional opal–VO2 photonic crystals were prepared by the chemical bath deposition technique. The x-ray diffraction and Raman spectroscopic data confirm the crystalline perfection of VO2 impregnated into synthetic opal pores. It is shown from the optical reflectivity measurements that the photonic bandgap of the opal–VO2 composite is governed by the phase transition in VO2. © 2001 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
71.30.+h Metal-insulator transitions and other electronic transitions
78.30.Hv Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Evanescent-wave acceleration of ultrashort electron pulses

Justyna Zawadzka, Dino A. Jaroszynski, John J. Carey, and Klaas Wynne

Appl. Phys. Lett. 79, 2130 (2001); http://dx.doi.org/10.1063/1.1406562 (3 pages) | Cited 4 times

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High-power femtosecond laser pulses have been used to excite surface plasmons in 500 Å silver and gold films. Nonlinear excitation results in the emission of electron bunches through multiphoton excitation at low power and laser-induced field emission at high power. The energies of photoelectrons are found to extend as high as 0.4 keV. Calculations show that these high energies are due to ponderomotive acceleration in an evanescent field extending from the metal film out into the vacuum. The theoretical calculations suggest that femtosecond electron pulses with relativistic energies can be generated using longer wavelengths or by developing the surface morphology. © 2001 American Institute of Physics.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
79.70.+q Field emission, ionization, evaporation, and desorption
79.60.Dp Adsorbed layers and thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Dispersive electron transport in an electroluminescent polyfluorene copolymer measured by the current integration time-of-flight method

Alasdair J. Campbell, Donal D. C. Bradley, and Homer Antoniadis

Appl. Phys. Lett. 79, 2133 (2001); http://dx.doi.org/10.1063/1.1406143 (3 pages) | Cited 118 times

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Here, we report results of both traditional current mode and current integration mode time-of-flight (TOF) measurements on the electroluminescent polyfluorene copolymer poly(9,9-dioctylfluorene-co-benzothiadiazole) (BT). Current mode TOF shows a strong but dispersive electron transport signal. The mobility derived from the current integration mode transit time (tQ) increases with decreasing film thickness as expected for dispersive transport. The fastest carriers in the photogenerated carrier packet are estimated to have mobilities of order 10−3 cm2/V s at applied fields of 0.5 MV/cm. Holes are heavily trapped close to the interface at which they are photogenerated. The TOF signals decay with repeated measurement and tQ remains constant with applied field. The transport properties of BT are thus in complete contrast to those of other polyfluorenes which show high-mobility nondispersive hole transport but weak and highly dispersive electron transport. © 2001 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Le Polymers; organic compounds (including organic semiconductors)
42.70.Jk Polymers and organics
72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

High-quality distributed Bragg reflectors based on AlxGa1−xN/GaN multilayers grown by molecular-beam epitaxy

S. Fernández, F. B. Naranjo, F. Calle, M. A. Sánchez-García, E. Calleja, P. Vennegues, A. Trampert, and K. H. Ploog

Appl. Phys. Lett. 79, 2136 (2001); http://dx.doi.org/10.1063/1.1401090 (3 pages) | Cited 13 times

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Distributed Bragg reflectors based on AlxGa1−xN/GaN multilayer stacks have been grown by plasma-assisted molecular-beam epitaxy on GaN templates. The nominal Al composition ranged from 30% to 45%, and the layer thicknesses of the ten-period stack were designed for a target wavelength of 510 nm. Transmission electron microscopy data reveal periodic structures where (Al,Ga)N on the GaN interface is sharper than GaN on the (Al,Ga)N one. X-ray diffraction spectra fitted to a dynamic diffraction simulation model yield an estimate of the layer thicknesses, Al%, and lattice strain. Reflectivity values above 50% at 510 nm have been reproducibly achieved, in very good agreement with the results of the matrix-method simulation. © 2001 American Institute of Physics.
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42.79.Bh Lenses, prisms and mirrors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.79.Wc Optical coatings
68.65.Ac Multilayers
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.40.Fy Semiconductors
52.77.Dq Plasma-based ion implantation and deposition
85.60.Jb Light-emitting devices

High-accuracy wavemeter based on a stabilized diode laser

Ayan Banerjee, Umakant D. Rapol, Ajay Wasan, and Vasant Natarajan

Appl. Phys. Lett. 79, 2139 (2001); http://dx.doi.org/10.1063/1.1408279 (3 pages) | Cited 25 times

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We have built a high-accuracy wavelength meter for tunable lasers using a scanning Michelson interferometer and a reference laser of known wavelength. The reference laser is a frequency-stabilized diode laser locked to an atomic transition in Rb. The wavemeter has a statistical error per measurement of 5 parts in 107, which can be reduced considerably by averaging. Using a second stabilized diode laser, we have verified that systematic errors are below 4 parts in 108. © 2001 American Institute of Physics.
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42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
07.60.Ly Interferometers
06.20.F- Units and standards

Eu3+-doped microcavities fabricated by sol–gel process

J. Bellessa, S. Rabaste, J. C. Plenet, J. Dumas, J. Mugnier, and O. Marty

Appl. Phys. Lett. 79, 2142 (2001); http://dx.doi.org/10.1063/1.1405427 (3 pages) | Cited 20 times

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The fabrication of microcavities by a sol–gel process and their optical properties are described. The cavities are constituted of an Eu3+-doped SiO2 active layer inserted between two Bragg mirrors, fabricated by stacking alternatiely undoped TiO2 and SiO2 sol–gel thin films. Eu3+ luminescence modification due to the cavity effect, intensity enhancement and modification of the line shape has been observed, and shows a cavity quality factor of 1200. The reflectivity factor of the associated Bragg mirrors reaches 99.8% for seven alternate SiO2/TiO2 layers. © 2001 American Institute of Physics.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
71.55.Ht Other nonmetals
68.55.-a Thin film structure and morphology
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Pulsed inductively coupled chlorine plasmas in the presence of a substrate bias

Pramod Subramonium and Mark J. Kushner

Appl. Phys. Lett. 79, 2145 (2001); http://dx.doi.org/10.1063/1.1406139 (3 pages) | Cited 9 times

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Pulsed inductively coupled plasmas (ICPs) sustained in electronegative gas mixtures using a substrate bias are being investigated to achieve improved etching characteristics in microelectronics fabrication. Experiments have shown that electron temperatures in pulsed ICPs without a substrate bias monotonically decrease during the afterglow. Under select conditions with a substrate bias, electron temperatures increase in the late afterglow. These trends suggest a transition in power deposition from inductive to capacitive. To investigate these processes, a two-dimensional, computationally parallel model was developed for pulsed ICPs. Results for Cl2 plasmas indicate that with a substrate bias the sheath thickness and speed, and hence electron heating, increase during the afterglow as the electron density decays. When the sheath reaches a critical thickness, capacitive electron heating begins. © 2001 American Institute of Physics.
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52.50.Dg Plasma sources
52.77.Bn Etching and cleaning
52.65.Pp Monte Carlo methods
52.40.Kh Plasma sheaths
52.80.Hc Glow; corona
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Effect of thermal processing on strain relaxation and interdiffusion in Si/SiGe heterostructures studied using Raman spectroscopy

S. J. Koester, K. Rim, J. O. Chu, P. M. Mooney, J. A. Ott, and M. A. Hargrove

Appl. Phys. Lett. 79, 2148 (2001); http://dx.doi.org/10.1063/1.1405151 (3 pages) | Cited 27 times

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The effect of thermal annealing on Si/SiGe heterostructures is studied using Raman spectroscopy. The structures consisted of Si on relaxed Si0.8Ge0.2 where the top Si thickness was 20–30 nm. Micro-Raman spectroscopy with 488 nm incident radiation revealed no significant shift in the strained Si peak position with thermal annealing at temperatures up to 1100 °C for 30 s. However, the intensity of the Si peak was systematically reduced with increasing thermal processing, a result which is attributed to interdiffusion at the Si/SiGe interface resulting in an apparent thinning of the Si cap layer. © 2001 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
78.66.Db Elemental semiconductors and insulators
61.72.Cc Kinetics of defect formation and annealing
78.30.Am Elemental semiconductors and insulators
68.60.Bs Mechanical and acoustical properties

Time-resolved photoluminescence of ytterbium-doped nanocrystalline Si thin films

Xinwei Zhao and Shuji Komuro

Appl. Phys. Lett. 79, 2151 (2001); http://dx.doi.org/10.1063/1.1404410 (3 pages)

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Ytterbium-doped nanocrystalline silicon (nc-Si) thin films were formed on Si and quartz substrates by ablating a Si:Yb2O3 mixture target. The Yb-doped nc-Si showed sharp emission peaks at wavelengths around 1 μm. Time-resolved photoluminescence measurements indicated that the Yb3+ ions were excited through an energy transfer process due to the photoinduced carriers in the host nc-Si. A clear delay on the rise time of the Yb emission from the recombination of the host carriers was observed, also suggesting an indirect excitation of the Yb3+ ions. These results showed a possibility of exciting Yb3+ ions by carrier injection. © 2001 American Institute of Physics.
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42.79.Wc Optical coatings
78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
78.30.Am Elemental semiconductors and insulators

Effects of excitation density on cathodoluminescence from GaN

S. O. Kucheyev, M. Toth, M. R. Phillips, J. S. Williams, and C. Jagadish

Appl. Phys. Lett. 79, 2154 (2001); http://dx.doi.org/10.1063/1.1408273 (3 pages) | Cited 19 times

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Wurtzite GaN epilayers are studied by cathodoluminescence (CL) spectroscopy. Results show that the intensities of donor–acceptor pair (DAP) and yellow luminescence (YL) peaks sublinearly depend on excitation density, presumably, due to saturation effects. The intensity of near-gap emission, however, exhibits a superlinear dependence on electron-beam excitation. In contrast to photoluminescence measurements, CL studies of GaN are usually performed in a regime with a strongly nonlinear dependence of luminescence intensities on excitation due to a large difference in carrier generation rates for these two techniques. As a result, the ratios of near-gap to YL and DAP emission intensities strongly depend on electron-beam current. Moreover, electron-beam spot size (i.e., beam focusing) dramatically affects CL intensity. An understanding of such saturation effects is necessary for a correct interpretation of CL spectra from GaN. © 2001 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors

Bimodal distribution of Indium composition in arrays of low-pressure metalorganic-vapor-phase-epitaxy grown InGaAs/GaAs quantum dots

G. Saint-Girons, G. Patriarche, L. Largeau, J. Coelho, A. Mereuta, J. M. Moison, J. M. Gérard, and I. Sagnes

Appl. Phys. Lett. 79, 2157 (2001); http://dx.doi.org/10.1063/1.1406553 (3 pages) | Cited 15 times

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Low-pressure metalorganic-vapor-phase-epitaxy (LP-MOVPE) grown InGaAs/GaAs quantum dots (QDs) emitting around 1.3 μm have been studied by photoluminescence and transmission electron microscopy (TEM). We demonstrate the presence of a bimodal inhomogeneous broadening of the photoluminescence, correlated with a bimodal QDs contrast distribution in the TEM micrographs. Increasing the growth temperature of the dots induces a decrease of the ratio between the number of In-poor and In-rich QDs, illustrating the crucial influence of indium desorption on the LP-MOVPE growth of InGaAs QDs. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.43.Mn Adsorption kinetics

Measurement of quantum efficiency in Pr3+-doped CaAl4O7 and SrAl4O7 crystals

Xiao-jun Wang, Shihua Huang, Lizhu Lu, William M. Yen, A. M. Srivastava, and A. A. Setlur

Appl. Phys. Lett. 79, 2160 (2001); http://dx.doi.org/10.1063/1.1407296 (3 pages) | Cited 5 times

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We demonstrated a method for measuring the quantum efficiency of deep UV emission using the two-step excitation and the difference of the integrated spectral intensities in Pr3+-doped CaAl4O7 and SrAl4O7 crystals. The quantum efficiencies of the emission from the lowest 4f5d state in the two systems have been estimated to be less than 10% at room temperature. The effect of excited-state absorption of the lowest 4f5d state is analyzed for the quantum efficiency measurement. The actual efficiency may be higher when this effect is taken into account, especially under the condition of strong excitation. © 2001 American Institute of Physics.
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78.40.Ha Other nonmetallic inorganics
42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.70.Hj Laser materials

On the dynamics of periodically-poled lithium niobate formation by off-center Czochralski technique

C. Sada, N. Argiolas, and M. Bazzan

Appl. Phys. Lett. 79, 2163 (2001); http://dx.doi.org/10.1063/1.1408603 (3 pages) | Cited 4 times

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The formation mechanisms which might be responsible for the domain structures observed in periodic-poled lithium niobate crystals grown by the off-center Czochralski technique were investigated varying the process parameters. We show that the periodic inverted domains structure does not maintain the polarization over the whole crystal, as commonly accepted. In particular, a “separation plane” parallel to the growth axis exists and divides the crystal in two halves, each with periodic structure but with opposite domain sequences. A possible explanation of the phenomenon is presented invoking both the thermoelectric effect and its correlation to the dynamic temperature fluctuation experienced by the growing crystal. © 2001 American Institute of Physics.
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81.10.Fq Growth from melts; zone melting and refining
72.20.Pa Thermoelectric and thermomagnetic effects

Piezoelectricity of ordered (Ga0.5In0.5)N alloys

A. Al-Yacoub and L. Bellaiche

Appl. Phys. Lett. 79, 2166 (2001); http://dx.doi.org/10.1063/1.1406983 (3 pages) | Cited 16 times

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First-principles calculations are performed to compare the e33 and e31 piezoelectric coefficients of GaN and InN with those of the (Ga0.5In0.5)N alloy exhibiting an alternation of Ga and In planes along the c axis. The magnitude of e33 and e31 in the ordered alloy is found to be (15%–28%) smaller than the magnitude of the corresponding coefficients resulting from the compositional average over the GaN and InN parent compounds. The microscopic origins for this downward deviation of piezoelectricity from a linear behavior with composition are revealed and discussed. © 2001 American Institute of Physics.
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77.65.-j Piezoelectricity and electromechanical effects
71.15.-m Methods of electronic structure calculations
72.80.Ey III-V and II-VI semiconductors

Hardness and elasticity in cubic ruthenium dioxide

J. M. Léger, P. Djemia, F. Ganot, J. Haines, A. S. Pereira, and J. A. H. da Jornada

Appl. Phys. Lett. 79, 2169 (2001); http://dx.doi.org/10.1063/1.1401786 (3 pages) | Cited 14 times

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The Knoop hardness of the highly incompressible cubic phase of ruthenium dioxide was found to be 19–20 GPa from indentation tests. This value scales well with the shear modulus approximated by the elastic constant C44 of 144 GPa obtained from Brillouin scattering measurements. This work provides evidence that the shear modulus is a better indicator of hardness than the bulk modulus for ionic and covalent materials. © 2001 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
62.20.M- Structural failure of materials
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Improvement of the photoluminescence properties in a-SiNx films by introduction of hydrogen

M. Molinari, H. Rinnert, and M. Vergnat

Appl. Phys. Lett. 79, 2172 (2001); http://dx.doi.org/10.1063/1.1408905 (3 pages) | Cited 11 times

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Photoluminescence properties of amorphous hydrogenated silicon nitride thin films with various compositions are presented. The as-deposited samples prepared by evaporation of silicon under a flow of nitrogen and hydrogen ions exhibit visible photoluminescence at room temperature without any annealing treatment. The evolution of the photoluminescence properties with increasing nitrogen concentration in the films is correlated to structural investigations performed with Fourier-transform infrared spectroscopy and optical characterization obtained from transmission measurements in the ultraviolet-visible-near-infrared range. It is shown that the introduction of hydrogen is of prime importance to improve the photoluminescence intensity of the films. © 2001 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.55.Hx Other solid inorganic materials
81.05.Gc Amorphous semiconductors
78.35.+c Brillouin and Rayleigh scattering; other light scattering
68.55.-a Thin film structure and morphology

Electronic and optical properties of the (FeOs)Si2 ternaries

D. B. Migas and Leo Miglio

Appl. Phys. Lett. 79, 2175 (2001); http://dx.doi.org/10.1063/1.1408907 (3 pages) | Cited 4 times

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In this letter, we discuss the interesting changes in the band structure of two ternary (FeOs)Si2 configurations with respect to the isostructural binary β-FeSi2 and OsSi2 compounds. Our first-principle calculations also demonstrate that one of the ternaries is a direct-bandgap semiconductor with an appreciable value of the oscillator strength of the first direct transition at 0.78 eV. © 2001 American Institute of Physics.
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71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Raman microscopy determination of phase composition in polyfluorene composites

R. Stevenson, A. C. Arias, C. Ramsdale, J. D. MacKenzie, and D. Richards

Appl. Phys. Lett. 79, 2178 (2001); http://dx.doi.org/10.1063/1.1407863 (3 pages) | Cited 28 times

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Confocal Raman spectroscopy with a spatial resolution of ⩽ 1 μm is used to determine the composition of binary polyfluorene composites with micro- and mesoscale phase separation. The phases are found to contain significant proportions of both constituents, implying that exciton dynamics such as charge and energy transfer may occur within a particular phase. The results presented here provide an insight into thin-film phase separation of conjugated polymer blends of interest for optoelectronic device applications. In particular, in this letter the high degree of intraphase mixing is discussed in relation to the relatively high efficiency of photovoltaic devices fabricated from these blends. © 2001 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
78.30.Jw Organic compounds, polymers
64.75.-g Phase equilibria
42.70.Jk Polymers and organics
71.35.-y Excitons and related phenomena

Selective Si epitaxial growth technique employing atomic hydrogen and substrate temperature modulation

T. W. Schroeder, P. F. Ma, A. M. Lam, Y.-J. Zheng, and J. R. Engstrom

Appl. Phys. Lett. 79, 2181 (2001); http://dx.doi.org/10.1063/1.1408271 (3 pages) | Cited 1 time

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We present here a low-temperature (Ts<630 °C) process for the selective epitaxial growth of Si that employs atomic hydrogen. Modulation of both the substrate temperature and the flux of atomic hydrogen gives alternating growth and suppression/etching cycles, resulting in a significant increase in selectivity. Epitaxial thin-film quality is essentially unaffected, as verified by in situ analysis via low-energy electron diffraction, and ex situ analysis via scanning electron and atomic-force microscopy. © 2001 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

In situ investigations of the metal/silicon reaction in Ti/Si thin films capped with TiN: Volumetric analysis of the C49–C54 transformation

B. Chenevier, O. Chaix-Pluchery, I. Matko, J. P. Sénateur, R. Madar, and F. La Via

Appl. Phys. Lett. 79, 2184 (2001); http://dx.doi.org/10.1063/1.1406141 (3 pages) | Cited 3 times

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The thermal expansion coefficients associated with the C49 and C54 crystal directions have been determined by in situ x-ray diffraction analysis of Ti film annealing deposited on Si substrates. Evidence of a clear anisotropy in the C49 coefficients has been obtained: the αb is considerably smaller than αa and αc. The volume expansion is larger in C54: this contributes to reduce to 1.6% at the transformation temperature, the observed 2.0% volume difference at 300 K. The magnitude of the volume discontinuity during transformation is an indication for a first-order transition. © 2001 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
85.40.Ls Metallization, contacts, interconnects; device isolation
65.40.De Thermal expansion; thermomechanical effects
68.60.Dv Thermal stability; thermal effects
68.55.Nq Composition and phase identification
64.70.K- Solid-solid transitions
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Microstructural and optical properties of SnO2 thin films grown on heavily doped n-InP(100) substrates

T. W. Kim, D. U. Lee, D. C. Choo, and Y. S. Yoon

Appl. Phys. Lett. 79, 2187 (2001); http://dx.doi.org/10.1063/1.1403663 (3 pages) | Cited 7 times

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Bright-field transmission electron microscopy (TEM) and high-resolution TEM images and an electron diffraction pattern showed that the SnO2 layers grown on heavily doped n-InP(100) substrates were nanoscale thin films. X-ray photoelectron spectroscopy showed that the positions of the peaks corresponding to the Sn 3d5/2, the Sn 3d3/2, and the O 1s levels for the SnO2 thin film were slightly shifted toward the lower energy side in comparison with those for bulk SnO2. The refractive indices obtained by spectroscopic ellipsometry were above 2.2 around the SnO2 energy gap of the SnO2 thin films. The maximum intensity of the optical transmittance for the SnO2 nanoscale thin film with 3939 Å thickness was above 90%. © 2001 American Institute of Physics.
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78.66.Li Other semiconductors
07.60.Hv Refractometers and reflectometers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.05.js X-ray photoelectron diffraction
42.79.Wc Optical coatings
07.60.Fs Polarimeters and ellipsometers

Electrical transport through individual DNA molecules

Xin-Qi Li and YiJing Yan

Appl. Phys. Lett. 79, 2190 (2001); http://dx.doi.org/10.1063/1.1407860 (3 pages) | Cited 49 times

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A theoretical model is presented to describe electrical transport through individual DNA molecules. By contacting the proposed model with the experimentally measured data, a variety of valuable quantities are identified. The partially decoherent nature on the guanine–cytosine (GC) pairs of DNA is also elaborated in contrast to the completely incoherent hopping mechanism discussed in the context of charge transfer experiments. © 2001 American Institute of Physics.
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87.14.G- Nucleic acids

Giant microwave photoresistance of two-dimensional electron gas

P. D. Ye, L. W. Engel, D. C. Tsui, J. A. Simmons, J. R. Wendt, G. A. Vawter, and J. L. Reno

Appl. Phys. Lett. 79, 2193 (2001); http://dx.doi.org/10.1063/1.1408910 (3 pages) | Cited 84 times

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We measure microwave frequency (4–40 GHz) photoresistance at low magnetic field B, in high mobility two-dimensional electron gas samples, excited by signals applied to a transmission line fabricated on the sample surface. Oscillatory photoresistance vs B is observed. For excitation at the cyclotron resonance frequency, we find a giant relative photoresistance ΔR/R of up to 250%. The photoresistance is apparently proportional to the square root of applied power, and disappears as the temperature is increased. © 2001 American Institute of Physics.
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73.50.Mx High-frequency effects; plasma effects
76.40.+b Diamagnetic and cyclotron resonances
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

dc and rf performance of proton-irradiated AlGaN/GaN high electron mobility transistors

B. Luo, J. W. Johnson, F. Ren, K. K. Allums, C. R. Abernathy, S. J. Pearton, R. Dwivedi, T. N. Fogarty, R. Wilkins, A. M. Dabiran, A. M. Wowchack, C. J. Polley, P. P. Chow, and A. G. Baca

Appl. Phys. Lett. 79, 2196 (2001); http://dx.doi.org/10.1063/1.1408606 (3 pages) | Cited 45 times

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AlGaN/GaN high electron mobility transistors (HEMTs) with a range of gate lengths (0.8–1.2 μm) and widths (100–200 μm) were exposed to 40 MeV protons at fluences of 5×109 or 5×1010 cm−2. The drain–source currents in the devices decreased by 15%–20% at the higher fluence, while the extrinsic transconductance decreased by ∼30% under the same conditions. Based on the increases in the reverse breakdown voltage and the channel resistance, the main degradation mechanism is believed to be creation of deep trap states in the band gap which remove electrons from the channel. The maximum frequency of oscillation, fMAX, also decreased as a result of the proton-induced damage, with a change of −20% at the shorter gate widths and −50% at the largest widths. The reverse recovery switching time was essentially unaffected by the irradiation, remaining at ∼ 1.6×10−8 s. Postradiation annealing at 800 °C was successful in restoring the dc and rf performance parameters to ⩾90% of their original values. The AlGaN/GaN HEMTs are much more robust than their AlGaAs/GaAs counterparts to displacement damage and appear well-suited to radiation environment applications. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices
84.40.-x Radiowave and microwave (including millimeter wave) technology
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
71.55.Eq III-V semiconductors

Surface passivation of p-type crystalline Si by plasma enhanced chemical vapor deposited amorphous SiCx:H films

I. Martín, M. Vetter, A. Orpella, J. Puigdollers, A. Cuevas, and R. Alcubilla

Appl. Phys. Lett. 79, 2199 (2001); http://dx.doi.org/10.1063/1.1404406 (3 pages) | Cited 46 times

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Excellent passivation properties of intrinsic amorphous silicon carbide (a-SiCx:H) films deposited by plasma enhanced chemical vapor deposition on single-crystalline silicon (c-Si) wafers have been obtained. The dependence of the effective surface recombination velocity, Seff, on deposition temperature, total pressure and methane (CH4) to silane (SiH4) ratio has been studied for these films using lifetime measurements made with the quasi-steady-state photoconductance technique. The dependence of the effective lifetime, τeff, on the excess carrier density, Δn, has been measured and also simulated through a physical model based on Shockley–Read–Hall statistics and an insulator/semiconductor structure with fixed charges and band bending. A Seff at the a-SiCx:H/c-Si interface lower than 30 cm s−1 was achieved with optimized deposition conditions. This passivation quality was found to be three times better than that of noncarbonated amorphous silicon (a-Si:H) films deposited under equivalent conditions. © 2001 American Institute of Physics.
Show PACS
81.65.Rv Passivation
81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.25.+i Surface conductivity and carrier phenomena
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Pz Photoconduction and photovoltaic effects
52.77.Dq Plasma-based ion implantation and deposition
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