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26 Oct 1998

Volume 73, Issue 17, pp. 2393-2529

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Generation of picosecond hard x rays by tera watt laser focusing on a copper target

Masatake Yoshida, Yasushi Fujimoto, Yoichiro Hironaka, Kazutaka G. Nakamura, Ken-ichi Kondo, Masayuki Ohtani, and Hiroshi Tsunemi

Appl. Phys. Lett. 73, 2393 (1998); http://dx.doi.org/10.1063/1.122444 (3 pages) | Cited 41 times

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Hard x-ray generation from tera-watt laser irradiation (4 TW, 42 fs at 780 nm) on a solid copper target has been studied in a range of the laser-power density between 3×1016 and 2×1017 W/cm2. Short-pulsed x rays are generated within 6.4 ps and include Cu Kα and Kβ line emissions and a continuum between 3 and 6 keV. The maximum intensity of Cu Kα radiation has been estimated to be 6.5×1010 photons (4π sr pulse)−1. The mechanism of hard x-ray generation has been discussed. © 1998 American Institute of Physics.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.La X-ray and γ-ray measurements
06.60.Jn High-speed techniques (microsecond to femtosecond)

Two-dimensionally conjugated molecules: The importance of low molecular symmetry for large third-order nonlinear optical effects

U. Gubler, R. Spreiter, Ch. Bosshard, P. Günter, R. R. Tykwinski, and F. Diederich

Appl. Phys. Lett. 73, 2396 (1998); http://dx.doi.org/10.1063/1.122445 (3 pages) | Cited 18 times

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Low molecular symmetry with regard to the conjugation path of the delocalized electrons was found to be a good guideline towards linearly conjugated molecules with large second-order hyperpolarizabilities γ. We show that this guideline is also valid for two-dimensionally conjugated systems. We experimentally demonstrate this by third-harmonic generation measurements of two-dimensionally conjugated organic molecules, and show that the observed effects can be explained by the symmetry of the electronic wave functions. In addition, the positive impact of the substitution of phenyl rings by thienyl rings on γ is discussed. © 1998 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Nv Optical frequency converters
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

High-efficiency, low-drive-voltage, semitransparent stacked organic light-emitting device

G. Gu, V. Khalfin, and S. R. Forrest

Appl. Phys. Lett. 73, 2399 (1998); http://dx.doi.org/10.1063/1.122446 (3 pages) | Cited 44 times

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We report a semitransparent, two-color, stacked organic light-emitting device (SOLED) with high efficiency, low drive voltage, and minimal color distortion. The SOLED emits light from both device surfaces. The external quantum efficiencies of the green and red stacked elements are 1% and 0.4%, respectively, where only the photons emitted from the substrate surface are collected. The drive voltage for the top stack element is decreased to ∼12 V by using a modified indium tin oxide thin film deposition process. Color distortion and angular dependence of the emission spectra are minimal. © 1998 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

Selectable dual-wavelength pulses generated from a laser diode using external feedback from a two-chromatic fiber grating

Y. Zhao and C. Shu

Appl. Phys. Lett. 73, 2402 (1998); http://dx.doi.org/10.1063/1.122447 (3 pages) | Cited 4 times

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A simple, robust, and easily integrable external cavity is demonstrated for the generation of self-seeded dual-wavelength pulses at about 1550 nm. The key component for wavelength selection is a two-chromatic fiber grating. Dual-wavelength pulses with equal intensities at the wavelengths and side-mode-suppression ratio of about 18 dB are obtained. By controlling the bias current and the polarization state, the laser can also be switched into single wavelength oscillation. Discrete tuning of the dual-wavelength pulses has also been demonstrated over a total range of 12.1 nm while maintaining a constant spacing of 6.3 nm. © 1998 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.79.Dj Gratings
42.81.Wg Other fiber-optical devices

Very high-speed metal-semiconductor-metal ultraviolet photodetectors fabricated on GaN

J. C. Carrano, T. Li, D. L. Brown, P. A. Grudowski, C. J. Eiting, R. D. Dupuis, and J. C. Campbell

Appl. Phys. Lett. 73, 2405 (1998); http://dx.doi.org/10.1063/1.122448 (3 pages) | Cited 29 times

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We report on the temporal and the frequency response of metal-semiconductor-metal ultraviolet photodetectors fabricated on single-crystal GaN. The best devices show a fast 10%–90% rise time of ∼23 ps implying a bandwidth of >15 GHz. These time domain data have been corroborated by direct measurement of the power spectral content. From this a cutoff frequency, f3 dB, of ∼16 GHz has been obtained. Analysis in terms of reverse bias and geometric scaling indicates that the photodetectors are transit-time limited. Modeling of the temporal behavior indicates that a slow component in the time and frequency response data is a consequence of the hole drift velocity. © 1998 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.40.Sx Metal-semiconductor-metal structures
06.60.Jn High-speed techniques (microsecond to femtosecond)

Highly efficient photorefractive polymer-dispersed liquid crystals

A. Golemme, B. Kippelen, and N. Peyghambarian

Appl. Phys. Lett. 73, 2408 (1998); http://dx.doi.org/10.1063/1.122449 (3 pages) | Cited 19 times

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We report on high-resolution photorefractive polymer-dispersed liquid crystals that lead to high diffraction efficiency at lower applied fields compared with photorefractive polymers. The diffraction efficiency reaches 100% internally for 105-μm-thick samples at a field of 8 V/μm. Net optical gain and diffraction efficiencies of 56% are demonstrated in 53-μm-thick devices. Subsecond response times have also been obtained using polymeric matrices with good transport properties. © 1998 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Df Liquid crystals
42.70.Ln Holographic recording materials; optical storage media
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.40.Eq Holographic optical elements; holographic gratings
42.70.Jk Polymers and organics

All-optical liquid device derived from negative nonlinear absorption effect in an erbium chloride solution

Yoshinobu Maeda, Yoshiki Akidzuki, and Toshikazu Yamada

Appl. Phys. Lett. 73, 2411 (1998); http://dx.doi.org/10.1063/1.122450 (3 pages) | Cited 2 times

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The dependence of the negative nonlinear absorption effect on the modulation degree and frequency was investigated in an erbium chloride solution using a 807.6 nm laser diode. The reverse-phased wave forms were obtained in the transmitted wave form for sample lengths greater than 6 cm. Though the reverse-phased wave form was observed symmetrically at modulation frequency of 0.1 MHz, they were asymmetrical at higher than 0.25 MHz. The effect has a characteristic which is almost independent of the state of erbium ions because it is formed by optical transitions of the inner shell of the erbium atom. © 1998 American Institute of Physics.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.79.-e Optical elements, devices, and systems

Relationship between optical and structural properties in substituted quaterthiophene crystals

G. Gigli, M. Lomascolo, R. Cingolani, G. Barbarella, M. Zambianchi, L. Antolini, F. Della Sala, A. Di Carlo, and P. Lugli

Appl. Phys. Lett. 73, 2414 (1998); http://dx.doi.org/10.1063/1.122451 (3 pages) | Cited 12 times

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The optical properties of polysubstituted α-conjugated quaterthiophene crystals display marked differences depending on substitution pattern and molecular conformation. The combination of optical spectroscopy and x-ray diffraction elucidates the correlation among molecular functionalization, crystalline structure, and electronic states. The data are quantitatively interpreted by a semiempirical technique that provides the excited state energies starting from the measured molecular geometry. © 1998 American Institute of Physics.
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61.66.Hq Organic compounds
71.20.Rv Polymers and organic compounds
78.40.Me Organic compounds and polymers
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Electromechanical coupling coefficient for surface acoustic waves in proton-exchanged 128°-rotated Y-cut lithium niobate

D. Čiplys and R. Rimeika

Appl. Phys. Lett. 73, 2417 (1998); http://dx.doi.org/10.1063/1.122452 (3 pages) | Cited 4 times

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The attenuation of surface acoustic waves propagating along crystallographic X axis in proton-exchanged 128° rotated Y-cut lithium niobate during the evaporation of copper film on the crystal surface has been measured as a function of sheet resistivity of the film. From the magnitude of attenuation maxima, the effective electromechanical coupling coefficients for samples with different thicknesses of HxLi1−xNbO3 layers have been evaluated, and from the position of maxima in the resistivity scale, the effective dielectric permittivities of the structure have been estimated. The electromechanical coupling coefficient is found to be reduced practically to zero with increasing thickness of protonated layer and acoustic frequency, and the dielectric permittivity is not significantly affected by the proton exchange. © 1998 American Institute of Physics.
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77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
43.35.Pt Surface waves in solids and liquids
68.35.Gy Mechanical properties; surface strains
77.22.Ch Permittivity (dielectric function)
42.79.Jq Acousto-optical devices
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
73.61.Ng Insulators
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Relativistic electron-beam generation in a gas-loaded foil-less diode

Bao-Liang Qian, Chuan-Lu Li, Yong-Gui Liu, Jian-De Zhang, Qi-Mei Tan, Jin-Liang Liu, and Che-Bo Liu

Appl. Phys. Lett. 73, 2420 (1998); http://dx.doi.org/10.1063/1.122468 (3 pages) | Cited 1 time

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Relativistic electron beams were generated in a gas-loaded foil-less magnetized diode. The helium gas was employed to fill the diode, and the experimental results have shown that the diode operated normally without the closure problem when the gas pressure was below a certain value (typically, 100 mTorr in the presence of an externally applied guide magnetic field). It has been observed that the current of the electron beam could increase with increasing the gas pressure, and that the presence of helium gas could reduce the operating voltage of the diode producing an electron beam with lower kinetic energy, which implies a decrease in the diode impedance. The externally applied magnetic field along the axial direction also exerted an influence on the electron-beam generation in the gas-loaded diode. © 1998 American Institute of Physics.
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52.75.Fk Magnetohydrodynamic generators and thermionic convertors; plasma diodes
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
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Diamondlike carbon deposition on silicon using radio-frequency inductive plasma of Ar and C2H2 gas mixture in plasma immersion ion deposition

D. H. Lee, X. M. He, K. C. Walter, M. Nastasi, J. R. Tesmer, M. Tuszewski, and D. R. Tallant

Appl. Phys. Lett. 73, 2423 (1998); http://dx.doi.org/10.1063/1.122469 (3 pages) | Cited 23 times

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Diamondlike carbon (DLC) was deposited on silicon using a plasma immersion ion deposition (PIID) method. Inductive radio-frequency plasma sources were used to generate Ar and C2H2 plasmas at low gas pressures ranging from 0.04 to 0.93 Pa. The film stress and hardness were sharply dependent upon bias voltage at an operating pressure of 0.04 Pa. A maximum hardness of 30 GPa and compressive stress of 9 GPa was observed at a pulsed bias of −150 V bias (carbon energy of 80 eV). The mechanical properties of DLC films are correlated with UV Raman peak positions which infer sp3-bonded carbon contents. © 1998 American Institute of Physics.
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81.05.ub Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Tr Fullerenes and related materials
62.20.Qp Friction, tribology, and hardness

Te substitution in disordered dilute Se1−xTex alloys

A. K. Bhatnagar, Vipin Srivastava, and K. V. Reddy

Appl. Phys. Lett. 73, 2426 (1998); http://dx.doi.org/10.1063/1.122470 (3 pages) | Cited 3 times

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Photoacoustic absorption measurements at room temperature are reported for Se1−xTex alloys in both crystalline and amorphous states for 0<x ⩽ 0.3. The optical energy gap thus measured shows two features: (a) the gap decreases linearly as x increases with a change of slope at x = 0.1 for both crystalline and amorphous alloys; and (b) the difference in the gaps corresponding to the amorphous and crystalline phase remains remarkably constant over the entire range of x(0–0.3) studied here. We attribute the result (a) to the onset of “quantum percolation” at x = 0.1, and deduce from (b) that introduction of Te apparently does not affect the structural disorder. The results are argued to yield vital information about the restrictive nature of Te substitution into host Se. © 1998 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
61.43.Fs Glasses
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
71.55.Jv Disordered structures; amorphous and glassy solids
78.40.Pg Disordered solids
78.40.Fy Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

The thickness dependence of the flow stress of capped and uncapped polycrystalline Ag thin films

Mauro J. Kobrinsky and Carl V. Thompson

Appl. Phys. Lett. 73, 2429 (1998); http://dx.doi.org/10.1063/1.122471 (3 pages) | Cited 30 times

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The flow stress of capped and uncapped polycrystalline silver films on oxidized silicon wafers is reported as a function of Ag film thickness (in the range of 0.2–1.2 μm) and temperature (in the range of −50–500 °C). While the flow stress in capped films increases with decreasing film thickness, the flow stress in uncapped films increases when film thickness is decreased from 1.2 to 0.5 μm, but then decreases with further decreases in film thickness. A high temperature regime of purely plastic strain accommodation extends to lower temperatures in thinner uncapped films than in capped films, with a transition temperature to elastoplastic behavior characterized by an apparent activation energy consistent with diffusive mechanisms of strain relief. These results suggest that surface diffusion to, and down, grain boundaries (whose spacing scale with film thickness) mediates strain accommodation in uncapped films. © 1998 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
83.10.Gr Constitutive relations
68.35.Fx Diffusion; interface formation
61.72.Mm Grain and twin boundaries

Characterization of pitting corrosion in aluminum films by light scattering

Y.-P. Zhao, C.-F. Cheng, G.-C. Wang, and T.-M. Lu

Appl. Phys. Lett. 73, 2432 (1998); http://dx.doi.org/10.1063/1.122472 (3 pages) | Cited 7 times

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We report a detailed study of the morphology of pits formed by corrosion of aluminum thin films using an in-plane light scattering technique. We show that the corrosion front of the Al thin film can be treated as a quasi-two-level random rough surface. Based on an elastic diffraction theory, we are able to determine the average depth, the area, and the density of pits, as well as the fractal dimension of the surface. Using the advantages of light scattering, one can quantify the morphological parameters of corroded films in situ and nondestructively. © 1998 American Institute of Physics.
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81.05.Bx Metals, semimetals, and alloys
81.65.Kn Corrosion protection
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Bz Metals and metallic alloys
68.60.Bs Mechanical and acoustical properties
68.35.B- Structure of clean surfaces (and surface reconstruction)

Site-selective radiation damage of collapsed carbon nanotubes

Vincent H. Crespi, Nasreen G. Chopra, Marvin L. Cohen, A. Zettl, and Velimir Radmilovíc

Appl. Phys. Lett. 73, 2435 (1998); http://dx.doi.org/10.1063/1.122473 (3 pages) | Cited 8 times

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Carbon nanotubes can flatten into collapsed tubes with bulbs along either edge. The strong anisotropy in the graphitic radiation damage threshold both explains the rapid destruction of face-on flattened nanotubes and can be exploited to selectively modify the structure of edge-on flattened nanotubes, thereby creating one-dimensional sp2 carbon with noncontinuous transverse boundary conditions. © 1998 American Institute of Physics.
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61.82.Rx Nanocrystalline materials
61.80.Fe Electron and positron radiation effects
61.80.Az Theory and models of radiation effects
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Observation of step bunches in units of 4 ML on vicinal Si(113) surfaces

Jian-hong Zhu, K. Brunner, and G. Abstreiter

Appl. Phys. Lett. 73, 2438 (1998); http://dx.doi.org/10.1063/1.122474 (3 pages) | Cited 7 times

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Step bunching with a bunching unit of a four-atomic step has been observed on vicinal Si(113) surfaces which are misoriented by 0.37° towards a direction about 36° off [math10]. A strong short-range attractive interaction and a long-range repulsive interaction between the four-atomic steps have been revealed. The influence of the repulsive interaction is observed even at about 700 °C. The bunching can be enhanced by optimizing the growth conditions followed by annealing. The experiments confirm the low surface energy of the Si(113) plane. © 1998 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Md Surface thermodynamics, surface energies
61.72.Cc Kinetics of defect formation and annealing
81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Octahedral boron nitride fullerenes formed by electron beam irradiation

D. Golberg, Y. Bando, O. Stéphan, and K. Kurashima

Appl. Phys. Lett. 73, 2441 (1998); http://dx.doi.org/10.1063/1.122475 (3 pages) | Cited 111 times

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Here we report on the formation of fullerenes with a reduced number of layers (typically ⩽ 3) in boron nitride (BN) which was subjected to in situ electron irradiation at 20 and 490 °C in a high resolution 300 kV transmission electron microscope (HRTEM). The BN fullerenes exhibited B/N stoichiometry of ∼ 1 as confirmed by electron energy loss spectroscopy using a 1 nm electron probe. The fullerene HRTEM images revealed rectangle-like shapes when viewed in specific projections, unlike the quasispherical carbon fullerene morphology. The octahedral BN fullerene model [O. Stéphan, Y. Bando, A. Loiseau, F. Willaime, N. Shramchenko, T. Tamiya, and T. Sato, Appl. Phys. A 67, 107 (1998)] is verified by the BN fullerene observations at different viewing angles. © 1998 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
61.80.Fe Electron and positron radiation effects
61.82.Rx Nanocrystalline materials
81.05.ub Fullerenes and related materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
79.20.Kz Other electron-impact emission phenomena
61.66.Bi Elemental solids
61.66.Dk Alloys
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Impact of the free electron distribution on the random telegraph signal capture kinetics in submicron n-metal–oxide–semiconductor field-effect transistors

N. B. Lukyanchikova, M. V. Petrichuk, N. P. Garbar, E. Simoen, and C. Claeys

Appl. Phys. Lett. 73, 2444 (1998); http://dx.doi.org/10.1063/1.122476 (3 pages) | Cited 7 times

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In this letter, the role of the free electron distribution on the capture kinetics of repulsive random telegraph signals in deep submicron n-channel metal–oxide–semiconductor field-effect transistors is studied. The inversion layer density and profile is varied by changing simultaneously the substrate and the gate bias of the transistor which is in linear operation at a constant drain current I. Detailed results are obtained for a class of repulsive trap centers when charged by an electron, which show a I−m variation of the capture time constant, with m>1. Such a nonstandard behavior can be understood in the framework of the Coulomb blockade model, whereby the image charge of the trapped carrier is stored on the gate electrode and in the inversion and depletion layer in the silicon substrate. As is shown here the capture time constant is a unique function of the ratio of the inversion layer surface density and the squared thickness of the inversion layer. © 1998 American Institute of Physics.
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85.30.Tv Field effect devices
72.70.+m Noise processes and phenomena
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Single- and multi-wall carbon nanotube field-effect transistors

R. Martel, T. Schmidt, H. R. Shea, T. Hertel, and Ph. Avouris

Appl. Phys. Lett. 73, 2447 (1998); http://dx.doi.org/10.1063/1.122477 (3 pages) | Cited 985 times

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We fabricated field-effect transistors based on individual single- and multi-wall carbon nanotubes and analyzed their performance. Transport through the nanotubes is dominated by holes and, at room temperature, it appears to be diffusive rather than ballistic. By varying the gate voltage, we successfully modulated the conductance of a single-wall device by more than 5 orders of magnitude. Multi-wall nanotubes show typically no gate effect, but structural deformations—in our case a collapsed tube—can make them operate as field-effect transistors. © 1998 American Institute of Physics.
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85.65.+h Molecular electronic devices
85.30.Tv Field effect devices
72.80.Rj Fullerenes and related materials

Green electroluminescence from Er-doped GaN Schottky barrier diodes

A. J. Steckl, M. Garter, R. Birkhahn, and J. Scofield

Appl. Phys. Lett. 73, 2450 (1998); http://dx.doi.org/10.1063/1.122478 (3 pages) | Cited 47 times

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Visible light electroluminescence (EL) has been obtained from Er-doped GaN Schottky barrier diodes. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources (for Ga, and Er) and a plasma source for N2. Al was utilized for both the Schottky (small-area) and ground (large-area) electrodes. Strong green light emission was observed under reverse bias, with weaker emission present under forward bias. The emission spectrum consists of two narrow green lines at 537 and 558 nm and minor peaks at 413 and at 666/672 nm. The green emission lines have been identified as Er transitions from the 2H11/2 and 4S3/2 levels to the 4I15/2 ground state and the blue and red peaks as the 2H9/2 and 4F9/2 Er transitions to the same ground state. The reverse bias EL intensity was found to increase linearly with bias current. © 1998 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions

Electrochemical determination of the ionization potential and electron affinity of poly(9,9-dioctylfluorene)

S. Janietz, D. D. C. Bradley, M. Grell, C. Giebeler, M. Inbasekaran, and E. P. Woo

Appl. Phys. Lett. 73, 2453 (1998); http://dx.doi.org/10.1063/1.122479 (3 pages) | Cited 327 times

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We report cyclic voltammetry measurements for the blue electroluminescent conjugated polymer poly(9,9-dioctylfluorene). Both oxidation and reduction potentials are determined and thus estimates of both the ionization potential Ip and electron affinity Ea of the polymer are obtained for the same sample under the same experimental conditions. We estimate Ip = 5.80 eV and Ea = 2.12 eV. These results disagree with the common assumption that Ea is, to good approximation, given by the difference between Ip and the optical gap. Measurements on indium tin oxide/polyfluorene/calcium light emitting diode structures are consistent with the deductions from the electrochemical data. © 1998 American Institute of Physics.
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82.80.Fk Electrochemical methods
42.70.Jk Polymers and organics
82.30.-b Specific chemical reactions; reaction mechanisms
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.60.Fi Electroluminescence

Reduction in defect density by annealing in hydrogenated tetrahedral amorphous carbon

N. M. J. Conway, A. Ilie, J. Robertson, W. I. Milne, and A. Tagliaferro

Appl. Phys. Lett. 73, 2456 (1998); http://dx.doi.org/10.1063/1.122480 (3 pages) | Cited 42 times

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Electronic applications of diamond-like carbon have been limited by its relatively high disorder and defect density. We find that the density of paramagnetic defects in hydrogenated tetrahedral amorphous carbon and the Urbach slope of the optical absorption edge can be reduced by annealing at 300 °C, with little effect on the optical gap. This leads to a reduction in the dark conductivity and an increase in the photosensitivity. The effect is attributed to the migration of hydrogen through the C–C network, to allow better passivation of dangling bonds and a modification of the more weakly bonded sp2 clusters with narrower local band gaps. © 1998 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
72.80.Ng Disordered solids
81.05.Gc Amorphous semiconductors
72.40.+w Photoconduction and photovoltaic effects
76.30.Mi Color centers and other defects
78.40.Fy Semiconductors
78.40.Pg Disordered solids
72.80.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors

Fluorine diffusion and accumulation in Si step-doped InAlAs layers

A. Wakejima, K. Onda, A. Fujihara, E. Mizuki, and M. Kanamori

Appl. Phys. Lett. 73, 2459 (1998); http://dx.doi.org/10.1063/1.122481 (3 pages) | Cited 3 times

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The quantitative relation between fluorine (F) accumulation and Si donor concentration in n-InAlAs layers on InP substrate was investigated for several kinds of step-doped InAlAs samples using secondary ion mass spectroscopy. From the depth profile of F and Si donors in a periodic i-/n-InAlAs sample, we found that F accumulates only in n-InAlAs layers, passing through i-InAlAs layers. We also found that the amount of F accumulation in an n-InAlAs layer depends on the Si doping concentration. The experimental results can be explained by considering two states of F. In one state, F is bound to a Si donor and immobile, and in the other it is free and can diffuse. © 1998 American Institute of Physics.
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61.72.S- Impurities in crystals
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.J- Diffusion of impurities
81.70.Jb Chemical composition analysis, chemical depth and dopant profiling
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Eq III-V semiconductors

Elimination of spectral shifts associated with tip-induced band bending in scanning tunneling spectroscopy of lightly doped silicon

Hai-An Lin, Ralph J. Jaccodine, and Michael S. Freund

Appl. Phys. Lett. 73, 2462 (1998); http://dx.doi.org/10.1063/1.122482 (3 pages) | Cited 11 times

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It has been demonstrated in this letter that spectral shifts arising from the tip-induced band bending on the lightly doped silicon can be eliminated by forming an accumulation layer in p-type silicon or an inversion layer in n-type silicon by using a Pt–Ir tip. Illumination is also required for n-type silicon in order to eliminate shifts associated with deep depletion caused by tunneling leakage currents. Using the approaches described herein, energy gaps of approximately 1.1 eV are determined for both p-type and n-type silicon. Furthermore, identical bias polarity is observed in current–voltage curves for both n-type and p-type silicon, and can be explained by the direction of the band bending induced by Pt–Ir on lightly doped samples. These results suggest that scanning tunneling spectroscopy can be used to reveal various features associated with surface states and bulk properties in lightly doped samples by using high work function metals such as Pt–Ir in place of lower work function metals such as W. © 1998 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
72.80.Cw Elemental semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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
71.55.Cn Elemental semiconductors
71.20.Mq Elemental semiconductors

Carbon diffusion in silicon

P. Werner, U. Gösele, H.-J. Gossmann, and D. C. Jacobson

Appl. Phys. Lett. 73, 2465 (1998); http://dx.doi.org/10.1063/1.122483 (3 pages) | Cited 25 times

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Carbon diffusion in silicon has been investigated by using a superlattice structure of carbon spikes (10 nm-wide, carbon concentration >1019 cm−3, spikes spaced 100 nm apart) grown epitaxially by Si molecular beam epitaxy. Samples were annealed in the range between 680 and 850 °C. The diffusive behavior of carbon was monitored by secondary ion mass spectrometry. Carbon diffusion profiles observed at temperatures above 800 °C show highly nonregular behavior. The diffusion results are interpreted in terms of the kick-out mechanism. © 1998 American Institute of Physics.
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66.30.J- Diffusion of impurities
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
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