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18 Jun 2001

Volume 78, Issue 25, pp. 3927-4046

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Efficient tunable luminescence of SiGe alloy sheet polymers

G. Vogg, A. J.-P. Meyer, C. Miesner, M. S. Brandt, and M. Stutzmann

Appl. Phys. Lett. 78, 3956 (2001); http://dx.doi.org/10.1063/1.1378315 (3 pages) | Cited 1 time

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Crystalline SiGe alloy sheet polymers were topotactically prepared from epitaxially grown calcium germanosilicide Ca(Si1−xGex)2 precursor films in the whole composition range. These polygermanosilynes are found to be a well-defined mixture of the known siloxene and polygermyne sheet polymers with the OH groups exclusively bonded to silicon. The optical properties determined by photoluminescence and optical reflection measurements identify the mixed SiGe sheet polymers as direct semiconductors with efficient luminescence tunable in the energy range between 2.4 and 1.3 eV. © 2001 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.30.Hv Other nonmetallic inorganics

Structural properties of a GaNxP1−x alloy: Raman studies

I. A. Buyanova, W. M. Chen, E. M. Goldys, H. P. Xin, and C. W. Tu

Appl. Phys. Lett. 78, 3959 (2001); http://dx.doi.org/10.1063/1.1380244 (3 pages) | Cited 9 times

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Raman measurements in backscattering configuration are employed to characterize the effect of nitrogen on the structural properties of a GaNxP1−x alloy with x ⩽ 3%. The following effects of N incorporation on the vibrational spectra of GaNP are observed. First, frequencies of GaP-like and GaN-like longitudinal optical phonons exhibit strong compositional dependence, due to a combined effect of alloying and biaxial strain. Second, a dramatic quenching of two-phonon Raman scattering and an emergence of zone-edge GaP-like vibrations are observed. These effects are tentatively attributed to a local distortion of the GaNP lattice and/or compositional disorder in the alloy. © 2001 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.20.K- Phonon interactions
68.55.-a Thin film structure and morphology

Determination of optical properties of nitrogen-doped hydrogenated amorphous carbon films by spectroscopic ellipsometry

Y. Hayashi, G. Yu, M. M. Rahman, K. M. Krishna, T. Soga, T. Jimbo, and M. Umeno

Appl. Phys. Lett. 78, 3962 (2001); http://dx.doi.org/10.1063/1.1374501 (3 pages) | Cited 6 times

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Nitrogen-doped hydrogenated amorphous carbon films have been deposited on silicon substrates by radio-frequency plasma-enhanced chemical vapor deposition using different N2/CH4 gas ratios from 0 to 3. The real and imaginary parts, n and k, of the complex index of refraction of these films have been determined for wavelengths between 300 and 830 nm by spectroscopic ellipsometry. Excellent agreement has been found between measured and modeled spectra, in which an empirical dielectric function based on classical Lorentz oscillator and Tauc joint density of states, and a linear void distribution along the thickness of the films have been assumed. Decrease in the optical energy gap and increase in the extinction coefficient, k, with increase in nitrogen concentration have been observed. Refractive index, n, increases rapidly with increase in nitrogen concentration up to 6.8 at. % (∼7.0 at. %) and then increases slowly with further increase in nitrogen concentration. For all the samples, n is found to be highest at the film-substrate interface which gradually decreases towards the film surface. © 2001 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.66.Db Elemental semiconductors and insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Ultrafast carrier and phonon dynamics in ion-irradiated graphite

K. Ishioka, M. Hase, M. Kitajima, and K. Ushida

Appl. Phys. Lett. 78, 3965 (2001); http://dx.doi.org/10.1063/1.1379782 (3 pages) | Cited 13 times

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The effect of defects on the dynamics of photoexcited carriers and coherent acoustic phonon in graphite is investigated by means of reflectivity measurements with femtosecond time resolution. Point defects are introduced by irradiating graphite with 5 keV He+ ions. Introduction of the defects enhances the carrier relaxation by opening a decay channel via vacancy states, which competes efficiently with carrier–phonon scattering. The coherent phonon relaxation is also accelerated due to an additional scattering by defects. The linear fluence dependence of the decay rate is understood as scattering of propagating acoustic phonon by single vacancies. © 2001 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.82.Ms Insulators
78.47.-p Spectroscopy of solid state dynamics
63.20.K- Phonon interactions
61.72.J- Point defects and defect clusters
72.40.+w Photoconduction and photovoltaic effects

Photocatalysis of sculptured thin films of TiO2

Motofumi Suzuki, Tadayoshi Ito, and Yasunori Taga

Appl. Phys. Lett. 78, 3968 (2001); http://dx.doi.org/10.1063/1.1380730 (3 pages) | Cited 50 times

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Enhanced surface reaction efficiency has been demonstrated in the photocatalysis of obliquely deposited TiO2 thin films with variously shaped columns such as zigzag, cylinder, and helix. The columnar thickness and spacing play an important role in the enhancement of the effective surface area, while the columnar shape is less important. The optimum morphology for a surface reaction has been obtained at the deposition angle α = 70°, where the photocatalytic activity is 2.5 times larger than that at α = 0°. The morphology controlled obliquely deposited thin films are applicable for solar cell, electro- and photochromic devices besides photocatalyst. © 2001 American Institute of Physics.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.50.Hp Processes caused by visible and UV light
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology

Theory of lithographically-induced self-assembly

Z. Suo and J. Liang

Appl. Phys. Lett. 78, 3971 (2001); http://dx.doi.org/10.1063/1.1380728 (3 pages) | Cited 26 times

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Recent experiments show that, when a two-phase fluid confined between parallel substrates is subject to an electric field, one phase can self-assemble into a triangular lattice of islands in another phase. We describe a theory of the stability of the island lattice. It is well known that the total interface energy reduces when the island diameter increases. We show that, under certain conditions, the electrostatic free energy reduces when the island diameter decreases. The islands select the equilibrium diameter to minimize the combined interface energy and electrostatic energy. We describe the conditions for electrostatic field to stabilize the island lattice, and analyze an idealized model. The theory suggests considerable experimental control over stable island size. © 2001 American Institute of Physics.
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81.16.Dn Self-assembly
81.16.Nd Micro- and nanolithography
68.55.-a Thin film structure and morphology
85.40.Hp Lithography, masks and pattern transfer
81.15.Aa Theory and models of film growth
68.03.Cd Surface tension and related phenomena
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Polarity dependence of hexagonal GaN films on two opposite c faces of Al2O3 substrate

Peide Han, Zhanguo Wang, Xiaofeng Duan, and Ze Zhang

Appl. Phys. Lett. 78, 3974 (2001); http://dx.doi.org/10.1063/1.1380731 (3 pages) | Cited 11 times

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GaN films were grown in pairs on two opposite c faces of Al2O3 substrate by low-pressure metal-organic vapor phase epitaxy, and studied by scanning electron microscopy and converged beam electron diffraction. It is found that GaN film on the c-Al2O3 whose c face is forward to its crystal seed has [0001] polarity, and the other film on the c-Al2O3 whose c face is backward to its crystal seed has [000math] polarity. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Theoretical study of sulfur–hydrogen–vacancy complex in diamond

Takehide Miyazaki, Hideyo Okushi, and Tsuyoshi Uda

Appl. Phys. Lett. 78, 3977 (2001); http://dx.doi.org/10.1063/1.1381041 (3 pages) | Cited 13 times

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We present an ab initio study of sulfur (S)–hydrogen (H)–vacancy (V) complexes in diamond. An S–H–V defect may become a much shallower donor than an isolated substitutional S defect when S in the complex is either three or five connected. Upon annealing the S-doped crystal, preferential formation of other deep-level defects would deactivate the shallow S-complex donors. © 2001 American Institute of Physics.
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71.55.Cn Elemental semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.J- Point defects and defect clusters
61.72.Bb Theories and models of crystal defects
61.72.Yx Interaction between different crystal defects; gettering effect

Effect of growth stoichiometry on the electrical activity of screw dislocations in GaN films grown by molecular-beam epitaxy

J. W. P. Hsu, M. J. Manfra, S. N. G. Chu, C. H. Chen, L. N. Pfeiffer, and R. J. Molnar

Appl. Phys. Lett. 78, 3980 (2001); http://dx.doi.org/10.1063/1.1379789 (3 pages) | Cited 57 times

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The impact of the Ga/N ratio on the structure and electrical activity of threading dislocations in GaN films grown by molecular-beam epitaxy is reported. Electrical measurements performed on samples grown under Ga-rich conditions show three orders of magnitude higher reverse bias leakage compared with those grown under Ga-lean conditions. Transmission electron microscopy (TEM) studies reveal excess Ga at the surface termination of pure screw dislocations accompanied by a change in the screw dislocation core structure in Ga-rich films. The correlation of transport and TEM results indicates that dislocation electrical activity depends sensitively on dislocation type and growth stoichiometry. © 2001 American Institute of Physics.
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73.61.Ey III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.66.Bi Elemental solids
61.66.Dk Alloys

Normal-incidence spectroscopic ellipsometry for critical dimension monitoring

Hsu-Ting Huang, Wei Kong, and Fred Lewis Terry

Appl. Phys. Lett. 78, 3983 (2001); http://dx.doi.org/10.1063/1.1378807 (3 pages) | Cited 16 times

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In this letter, we show that normal-incidence spectroscopic ellipsometry can be used for high-accuracy topography measurements on surface relief gratings. We present both experimental and theoretical results which show that spectroscopic ellipsometry or reflectance-difference spectroscopy at near-normal incidence coupled with vector diffraction theory for data analysis is capable of high-accuracy critical dimension (CD), feature height, and sidewall angle measurements in the extreme submicron regime. Quantitative comparisons of optical and cross-sectional scanning electron microscopy (SEM) topography measurements from a number of 350 nm line/space reactive-ion-etched Si gratings demonstrate the strong potential for in situ etching monitoring. This technique can be used for both ex situ and in situ applications and has the potential to replace the use of CD-SEM measurements in some applications. © 2001 American Institute of Physics.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.60.Fs Polarimeters and ellipsometers

Specular reflection enhancement and reduction from the surface of a photorefractive crystal in the presence of a “pump” beam

Jiasen Zhang, Shin Yoshikado, and Tadashi Aruga

Appl. Phys. Lett. 78, 3986 (2001); http://dx.doi.org/10.1063/1.1381411 (3 pages)

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We demonstrate the enhancement and reduction of the specular reflection from the surface of a photorefractive crystal in the presence of a “pump” beam. The pump beam could be the phase conjugate beam of the input beam or another laser beam. The contribution of the reflection grating is also demonstrated in a 45°-cut crystal. The change of the specular reflection with respect to the intensity ratio of the input beam to the pump beam is measured. © 2001 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.68.+m Optical properties of surfaces
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
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