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15 Dec 2000

Volume 88, Issue 12, pp. 6973-7369

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Spatial coherence of azimuthally symmetric Gaussian electromagnetic beams

S. R. Seshadri

J. Appl. Phys. 88, 6973 (2000); http://dx.doi.org/10.1063/1.1326472 (8 pages) | Cited 2 times

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The spatial coherence properties of azimuthally symmetric electromagnetic beams launched by planar Gaussian sources are investigated. The intensity distribution and the coherence properties of the source do not vary in the azimuthal direction. A procedure is postulated for obtaining the root mean squared coherence length as a function of position in a plane transverse to the propagation direction. The variation of the root mean squared coherence length with the position in a transverse plane as well as along the propagation direction is treated. The dependence of these variations on the source coherence parameter relative to the beam waist at the source plane is discussed. On propagation, the root mean squared coherence length at any point in a transverse plane other than on the beam axis is found to vary in the azimuthal direction although cylindrical symmetry is preserved with respect to the variation of the location of the point in the azimuthal direction. © 2000 American Institute of Physics.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation

Origin of the wavelength-dependence of effective trap density in photorefractive BaTiO3:Ce

Hongwei Song, S. X. Dou, and Peixian Ye

J. Appl. Phys. 88, 6981 (2000); http://dx.doi.org/10.1063/1.1288782 (6 pages) | Cited 3 times

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The wavelength dependence of the total effective trap density, Neff, in a photorefractive BaTiO3:Ce crystal is experimentally determined by two-beam coupling. The result shows that Neff decreases with increasing wavelength. The deep-shallow-trap model for charge transport well fits to the experimental data, indicating that the model can quantitatively explain the variation of Neff with wavelength in BaTiO3:Ce. It is concluded that the remarkable variation of the ratio of the photo ionization cross section of the deep center to that of the shallow trap with wavelength, and the higher density of the shallow traps than that of the uncompensated deep centers are significant to the variation of Neff with wavelength. © 2000 American Institute of Physics.
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71.55.Ht Other nonmetals
42.70.Gi Light-sensitive materials

Transient thermal loading induced microbending loss in carbon-coated optical fibers

Yu-Ching Yang, Win-Jin Chang, and Haw-Long Lee

J. Appl. Phys. 88, 6987 (2000); http://dx.doi.org/10.1063/1.1323536 (6 pages) | Cited 9 times

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The transient microbending loss in a carbon-coated optical fiber, subjected to time-dependent thermal loading, is analyzed. First, the temperature distributions in the fiber and coating, which are varying with time, are derived. Then, the thermally induced, time-dependent compressive lateral pressure at the interface of the fiber and the coating is obtained. Finally, the transient microbending loss of the carbon-coated fiber is presented. It has been found that the transient microbending loss in the carbon-coated optical fiber increases with increasing Young’s modulus, Poisson’s ratio, and thermal expansion coefficient of the carbon coating. Therefore, in order to minimize the transient microbending loss of the carbon-coated optical fiber, the Young’s modulus, Poisson’s ratio, and thermal expansion coefficient of the carbon coating should be decreased. Nevertheless, there exists an optimum value for the thickness of the carbon coating to reduce the transient microbending loss and sustain the mechanical force at the same time. © 2000 American Institute of Physics.
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42.81.Dp Propagation, scattering, and losses; solitons
42.81.Bm Fabrication, cladding, and splicing
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
65.40.De Thermal expansion; thermomechanical effects
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Crystallization and optical nonlinearity in GeO2–SiO2 glass poled with ArF excimer-laser irradiation

Syuji Matsumoto, Takumi Fujiwara, Yoshiki Seno, Yosiharu Hirose, Motoshi Ohama, and Akira J. Ikushima

J. Appl. Phys. 88, 6993 (2000); http://dx.doi.org/10.1063/1.1328409 (4 pages) | Cited 2 times

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We report on crystallization and second- and third-order optical nonlinearities of GeO2–SiO2 glass poled with ArF laser irradiation. With laser power and 100 mJ/cm2/pulse, the treatment generates crystallites in the glass, provided that the poling field strength is greater than 0.5×105 V/cm. Its crystal structure is possibly the cristobalite phase of the Ge–Si–O system. A large coefficient of second-harmonic generation (SHG), d33, is induced in the glass with the crystallite generation, and its value is comparable to d22 of LiNbO3. Moreover, the third-order optical susceptibility χ(3) increases by a factor of approximately 15 compared to that of glass without the crystallites. Even after the d33 coefficient decays out, the crystallites and χ(3) are retained. The result suggests that the large SHG in the glass is not induced from inert second-order nonlinearity of the crystallites, but the main origin of the induction is the associated effective second-order nonlinearity with the formation of the space-charge field. © 2000 American Institute of Physics.
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64.70.K- Solid-solid transitions
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.An Optical susceptibility, hyperpolarizability
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.43.Fs Glasses
61.66.Fn Inorganic compounds
61.82.Ms Insulators

Far-field characteristics of mid-infrared angled-grating distributed feedback lasers

I. Vurgaftman, W. W. Bewley, R. E. Bartolo, C. L. Felix, M. J. Jurkovic, J. R. Meyer, M. J. Yang, H. Lee, and R. U. Martinelli

J. Appl. Phys. 88, 6997 (2000); http://dx.doi.org/10.1063/1.1326858 (9 pages) | Cited 17 times

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The far-field emission characteristics of mid-infrared angled-grating distributed-feedback (α-DFB) lasers with W active regions are calculated using a self-consistent beam-propagation formalism that is more general than previous analyses. The theoretical projections are compared with the results of an experimental study of optically pumped α-DFB devices. Near-diffraction-limited beam quality is obtained both theoretically and experimentally for pump stripes ⩽50 μm wide. While simulations employing the theoretical linewidth enhancement factor of 1.7 for the homogeneously-broadened W-laser gain spectrum predict that the good beam quality should be retained for stripes as wide as ≈200 μm, the data indicate a much more rapid degradation. That finding can be reproduced only by assuming that inhomogeneous broadening increases the structure’s linewidth enhancement factor to ≈5. The experiments and theory also yield a steering of the output beam to off-normal angles as large as 6° when temperature tuning shifts the gain peak away from the grating resonance. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Ah General laser theory
42.79.Dj Gratings
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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Raman spectroscopy of porous and bulk GaP subjected to MeV-ion implantation and annealing

A. Sarua, G. Irmer, J. Monecke, I. M. Tiginyanu, C. Schwab, J.-J. Grob, and H. L. Hartnagel

J. Appl. Phys. 88, 7006 (2000); http://dx.doi.org/10.1063/1.1322599 (7 pages) | Cited 8 times

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Porous layers on (100)-oriented n-type liquid encapsulated Czochralski grown GaP crystals were fabricated by electrochemical etching in a H2SO4 aqueous solution and analyzed by scanning electron microscopy. 12C+ ions were introduced at room temperature by 3 MeV energy implantation into porous and bulk samples at two ion doses of 1014 and 1015 cm−2. The prepared samples were annealed in the temperature range between 200 and 600 °C applying rapid thermal annealing (RTA) technique. A comparative micro-Raman study was carried out on the porous and bulk substances. Porosity was found to lead to the violation of the selection rules and to remarkable changes in the optical properties. Additionally, Fröhlich-type modes were observed in the Raman spectra of the porous layers. High energy implantation produces a thin high damaged layer, buried at the depth of the mean projected range. Implantation does not result in a drastic damage of the samples and they undergo a fast recovery after RTA. After this treatment a semi-insulating GaP layer is created, which is thermally stable up to 600 °C. © 2000 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
61.43.Gt Powders, porous materials
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
68.60.Dv Thermal stability; thermal effects

Nucleation and growth of C54 grains into C49 TiSi2 thin films monitored by micro-Raman imaging

S. Privitera, F. La Via, C. Spinella, S. Quilici, A. Borghesi, F. Meinardi, M. G. Grimaldi, and E. Rimini

J. Appl. Phys. 88, 7013 (2000); http://dx.doi.org/10.1063/1.1326469 (7 pages) | Cited 8 times

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The first-order C49–C54 allotropic-phase transition has been studied in TiSi2 thin films by electrical measurements and micro-Raman spectroscopy. To evaluate the parameters describing the kinetics of the transition and the barrier energy for the nucleation, micro-Raman spectroscopy has been used as a microscopy technique: spectra have been acquired scanning large silicide areas (100×50 μm2) and have been processed to obtain images which show the morphological evolution of the C54 grains during the transition. For temperatures between 680 and 720 °C, the converted area fraction has been determined at different annealing times and compared with electrical measurements. The two methods agree quite well. Both density and size of the C54 grains have been measured, thus allowing to separately determine the nucleation and growth parameters as a function of temperature. A nucleation and growth model has been fitted to data obtaining an activation energy of 4.9±0.7 eV for the nucleation rate and 4.5±0.9 eV for the growth velocity. Such values, coincident within experimental errors, indicate that the nucleation barrier energy for the transition to the C54 phase is very low. © 2000 American Institute of Physics.
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64.70.K- Solid-solid transitions
73.61.At Metal and metallic alloys
78.66.Bz Metals and metallic alloys
64.60.Q- Nucleation
68.55.-a Thin film structure and morphology
78.30.Er Solid metals and alloys
81.40.Gh Other heat and thermomechanical treatments

Structure of laser-crystallized Ge2Sb2+xTe5 sputtered thin films for use in optical memory

Noboru Yamada and Toshiyuki Matsunaga

J. Appl. Phys. 88, 7020 (2000); http://dx.doi.org/10.1063/1.1314323 (9 pages) | Cited 148 times

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The structure of laser-crystallized thin films of Ge2Sb2+xTe5 (0.0<x⩽1.0) formed by the sputtering method were identified by x-ray diffraction studies to be composed of two phases: one phase is chiefly NaCl type crystal with a lattice constant of about 6 Å and a composition corresponding to Ge2Sb2Te5; the other phase comprises a small amount of an amorphous component such as Sb metal. Results of the Rietveld and the whole-powder-pattern fitting analyses show good agreement when assuming that (i) the 4(a) site is wholly occupied by only Te, (ii) the 4(b) site is randomly occupied by Ge or Sb atoms, and (iii) a little less than 20% of the 4(b) site is always vacant independent of the x value. The above results and the fact that halo noise rises with x increasing from 0.0 to 1.0 indicate a more precise model of crystal structure as follows. That is, Sb atoms added beyond the stoichiometric ratio, Ge2Sb2Te5, never fill up the vacancies of the 4(b) site in the NaCl type structure; the excess Sb atoms will remain in the amorphous state and concentrate, for example, at the grain boundary. The authors conclude that the amounts of the amorphous component produced through the crystallization process predominantly determine the crystallization rates and the critical temperatures of Ge–Sb–Te amorphous films, reportedly that they show a gentle and continuous dependence on the compositional deviation from the GeTe–Sb2Te3 pseudobinary line. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
42.79.Vb Optical storage systems, optical disks
42.79.Wc Optical coatings
61.43.Er Other amorphous solids

Strain relaxation in AlGaN under tensile plane stress

S. Einfeldt, V. Kirchner, H. Heinke, M. Dießelberg, S. Figge, K. Vogeler, and D. Hommel

J. Appl. Phys. 88, 7029 (2000); http://dx.doi.org/10.1063/1.1326852 (8 pages) | Cited 41 times

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Relaxation of tensile strain in AlxGa1−xN layers of different compositions epitaxially grown on GaN/sapphire is investigated. Extended crack channels along 〈2math0〉 directions are formed if the aluminum content exceeds a critical value, which decreases with increasing layer thickness. This process is found to limit the average strain energy density to a maximum value of 4 J/m2. By calculating the stress distribution between cracks and the strain energy release rate for crack propagation, the relaxed strain as measured by x-ray diffraction is correlated to the crack density, and the onsets of crack channeling and layer decohesion are fitted to a fracture toughness of 9 J/m2. Moreover, the crack opening at the surface is found to linearly increase with the stress. Annealing of samples above the growth temperature introduces additional tensile stress due to the mismatch in thermal expansion coefficients between the layer and substrate. This stress is shown to relieve not only by the formation of additional cracks but also by the extension of cracks into the GaN layer and a thermal activated change in the defect structure. © 2000 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
62.20.F- Deformation and plasticity
81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

The deviatoric response of polymethylmethacrylate to one-dimensional shock loading

J. C. F. Millett and N. K. Bourne

J. Appl. Phys. 88, 7037 (2000); http://dx.doi.org/10.1063/1.1324699 (4 pages) | Cited 16 times

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Samples of polymethylmethacrylate have been deformed by one-dimensional shock waves during plate impact. Manganin stress gauges have been introduced into the samples in such orientation that renders them sensitive to the lateral component of stress during shock loading. In combination with known Hugoniot data, these results have been used to determine the variation of shear strength with increasing impact stress. It has been observed that over the measured stress range, shear strength increases with increasing longitudinal stress. Comparison with the work of others shows close agreement. We also note that there is a small yet significant reduction in lateral stress, and hence an increase in shear strength behind the shock front. We believe this to be a manifestation of the viscoplastic response of this material. Finally, we observe no change in mechanical behavior at ∼2.0 GPa, where others have noticed large changes in thermal and electronic responses. © 2000 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Effects of the relative proportion of ferromagnetic and charge-ordered phases on the metal–insulator transition temperature in La0.5Ca0.5Mn1−xGexO3

Run-Wei Li, Ji-Rong Sun, Zhi-Hong Wang, Shao-Ying Zhang, Ning Tang, and Bao-Gen Shen

J. Appl. Phys. 88, 7041 (2000); http://dx.doi.org/10.1063/1.1327600 (4 pages) | Cited 3 times

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Magnetic and transport properties of rare-earth manganites La0.5Ca0.5Mn1−xGexO3 with 0⩽x⩽0.1 have been investigated systematically. Doping Ge at Mn sites increases the metal–insulator transition temperature (TP) from 124 to 210 K with increasing x from 0 to 0.08. The introduction of Ge severely destroys the charge-ordered state and hardly affects the ferromagnetic ordering. For low-doped samples, TP is also increased dramatically by the magnetic field, especially in the field-cooled mode. Magnetic analysis suggests the coexistence of the charge-ordered antiferromagnetic phase and the ferromagnetic phase. We propose that the proportion of the ferromagnetic phase and the charge-ordered phase can affect TP in phase-separated compounds. The phase diagram of La0.5Ca0.5Mn1−xGexO3 with 0⩽x⩽0.1 is presented. © 2000 American Institute of Physics.
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71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Determination of arsenic diffusion parameters by sulfur indiffusion in gallium arsenide

R. F. Scholz, P. Werner, U. Gösele, N. Engler, and H. S. Leipner

J. Appl. Phys. 88, 7045 (2000); http://dx.doi.org/10.1063/1.1325383 (6 pages) | Cited 2 times

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Indiffusion profiles of sulfur in gallium arsenide were determined by secondary ion mass spectroscopy. In order to evaluate the shape of the profiles, a set of coupled reaction–diffusion equations was solved numerically. From the simulated nonequilibrium indiffusion profiles of sulfur, which diffuses into gallium arsenide via the kick-out mechanism, both the diffusion coefficient and the equilibrium concentration of arsenic self-interstitials were simultaneously determined. Transmission electron microscopy revealed that, due to an arsenic supersaturation, extrinsic dislocation loops have formed. The Fermi-level effect is more pronounced at lower diffusion temperatures and provides an additional driving force for the loop formation, agreeing well with the occurrence of larger faulted loops at a diffusion temperature of 950 °C rather than at 1100 °C. The complex behavior of the sulfur indiffusion can be quantitatively described by taking into account extended defects. © 2000 American Institute of Physics.
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71.55.Eq III-V semiconductors
68.35.Fx Diffusion; interface formation
61.72.S- Impurities in crystals
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Be-enhanced CdSe island formation in CdSe/ZnSe heterostructures

M. Keim, M. Korn, J. Seufert, G. Bacher, A. Forchel, G. Landwehr, S. Ivanov, S. Sorokin, A. A. Sitnikova, T. V. Shubina, A. Toropov, and A. Waag

J. Appl. Phys. 88, 7051 (2000); http://dx.doi.org/10.1063/1.1328784 (5 pages) | Cited 11 times

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The Be-enhanced formation of CdSe quantum dots in CdSe/ZnSe heterostructures grown by migration enhanced epitaxy on (001)GaAs substrates has been investigated using photoluminescence spectroscopy, x-ray techniques (diffraction and reflectometry), and transmission electron microscopy. Coverage of the ZnSe starting surface with a fractional monolayer of beryllium selenide leads to enhanced island formation well below the CdSe thickness of 0.6 monolayer corresponding to the onset of the CdSe-rich island formation in the Be-free structures. The effect of the fractional Be coverage is demonstrated by observation of sharp lines in the photoluminescence signal from patterned mesas with dimensions down to 60 nm, which is due to the emission from individual exciton localization sites attributed to quantum dots. X-ray diffraction and reflectometry measurements on CdSe/ZnSe short-period superlattices with the submonolayer CdSe insertions confirm an enhanced roughening of the CdSe layer morphology in the case of beryllium coverage. Cross-sectional transmission electron microscopy on the SLs with BeSe fractional monolayer exhibits Cd-induced stress modulation along the CdSe sheets with a lateral scale of ∼4 nm, that can also be interpreted in favor of the BeSe-nucleated CdSe-based quantum dots. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Interface chemistry and electrical properties of SrVO3/LaAlO3 heterostructures

Dong-Wook Kim, Dae Ho Kim, T. W. Noh, K. Char, J.-H. Park, K.-B. Lee, and Hyeong-Do Kim

J. Appl. Phys. 88, 7056 (2000); http://dx.doi.org/10.1063/1.1326896 (4 pages) | Cited 2 times

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SrVO3 films were grown by laser molecular beam epitaxy on LaAlO3 substrates. For a 10-nm-thick film, its resistivity could be reduced by a factor of 4 by inserting a single La–O atomic layer on an oxygen-annealed LaAlO3 substrate. X-ray diffraction and x-ray photoelectron spectroscopy measurements revealed that oxygen defect concentrations could be varied significantly by controlling the substrate terminations, i.e., interface chemistry. It was suggested that the interface chemistry could influence formation of extended defects and result in changes in electrical properties. © 2000 American Institute of Physics.
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68.35.Ct Interface structure and roughness
68.35.Fx Diffusion; interface formation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
79.60.Jv Interfaces; heterostructures; nanostructures

Effect of temperature on carbon nitride films synthesized by ion-beam-assisted pulsed laser deposition

Z. Y. Chen, J. P. Zhao, T. Yano, T. Ooie, M. Yoneda, and J. Sakakibara

J. Appl. Phys. 88, 7060 (2000); http://dx.doi.org/10.1063/1.1326474 (7 pages) | Cited 8 times

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Carbon nitride thin films were deposited by pulsed laser deposition with nitrogen ion beam assistance at a substrate temperature varying from room temperature to 800 °C. The effect of the substrate temperature on the nitrogen content, surface morphology, structure, and electrical property of the carbon nitride films was investigated. The deposited films were characterized by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and four-probe resistance. The nitrogen content of the deposited films reached its maximum value of 25% at a substrate temperature of 400 °C. AFM images revealed that an island structure occurred and developed on the surface of the films deposited at the high substrate temperature. FTIR and XPS spectra showed the existence of sp3C–N and sp2C�N bonds in the deposited films. The deposited carbon nitride films had an amorphous structure with two carbon nitride phases inclusions, which had a stoichiometry near C3N4 and a variable stoichiometry from C5N to C2N, respectively. With the increase in substrate temperature, the relative content of the sp3C–N bonds, i.e., the C3N4 phase, increased and the crystallization degree of the deposited films enhanced, which were confirmed by the Raman analysis. Very few CN bonds in the films were found as compared to other carbon–nitrogen bonds. Electrical resistivity exhibited the highest value for the film deposited at 400 °C. Investigation results indicated that the high substrate temperature could promote the formation of C3N4 phase. © 2000 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.43.-j Disordered solids
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Nk Insulators
79.60.Ht Disordered structures
73.50.Fq High-field and nonlinear effects
73.61.Ng Insulators

Arsenic incorporation during Si(001):As gas-source molecular-beam epitaxy from Si2H6 and AsH3: Effects on film-growth kinetics

H. Kim, G. Glass, J. A. N. T. Soares, P. Desjardins, and J. E. Greene

J. Appl. Phys. 88, 7067 (2000); http://dx.doi.org/10.1063/1.1324701 (12 pages) | Cited 5 times

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The effects of As doping, at concentrations CAs⩽4.8×1018 cm−3, on the growth kinetics of Si(001):As layers deposited at temperatures Ts=575–900 °C by gas-source molecular-beam epitaxy from Si2H6 and AsH3 have been investigated. With constant AsH3 and Si2H6 fluxes, film deposition rates RSi increase while CAs decreases with increasing Ts. All incorporated As resides at substitutional electrically active sites for CAs up to 3.8×1018 cm−3 (Ts=800 °C), the highest value yet reported for Si(001):As growth from hydride source gases. Immediately following film growth or partial-monolayer As adsorption on clean Si(001), the samples were quenched to 300 °C and exposed to atomic deuterium (D) until saturation coverage. In situ D2 temperature-programmed desorption (TPD) spectra from both as-deposited Si(001):As and As-adsorbed Si(001) layers are composed of β1 and β2 peaks, due to D2 desorption from Si monodeuteride and dideuteride surface phases, together with a new peak β3 which we attribute to desorption from Si–As mixed dimers. Analyses of the TPD spectra show that, because of the lone-pair electrons associated with each As surface atom, the total dangling-bond coverage, and hence RSi, decreases with increasing incoming flux JAsH3 at constant Ts. From measurements of the steady-state As surface coverage θAs vs CAs and Ts, we obtain an As surface segregation enthalpy ΔHs=−0.92 eV. Dissociative AsH3 adsorption on Si(001) was found to follow second-order kinetics with a relatively Ts-independent reactive sticking probability of 0.3. Associative As2 desorption is also second order with a rate constant kd,As2=1×1013 exp(−3.0 eV/kTs). From the combined set of results, we develop a predictive model with no fitting parameters for CAs vs JAsH3, JSi2H6, and Ts. © 2000 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uf Ge and Si
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
64.75.-g Phase equilibria
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
65.20.-w Thermal properties of liquids
65.40.gd Entropy

Tensile stress evolution during deposition of Volmer–Weber thin films

Steven C. Seel, Carl V. Thompson, Sean J. Hearne, and Jerrold A. Floro

J. Appl. Phys. 88, 7079 (2000); http://dx.doi.org/10.1063/1.1325379 (10 pages) | Cited 70 times

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A simple model is presented that predicts the kinetics of tensile stress evolution during the deposition of thin films that grow by the Volmer–Weber mechanism. The generation of a tensile stress was attributed to the impingement and coalescence of growing islands, while concurrent stress relaxation was assumed to occur via a microstructure-dependent diffusive mechanism. To model the process of island coalescence, finite element methods were employed and yielded average tensile stresses more consistent with experimental observations than those predicted using previously reported analytical models. A computer simulation was developed that models the process of film growth as the continuous nucleation of isolated islands, which grow at a constant rate to impinge and coalesce to form a continuous polycrystalline film. By incorporating the finite element results for stress generation and a microstructure-dependent stress relaxation model, the simulation qualitatively reproduced the complex temperature-dependent trends observed from in situ measurements of stress evolution during the deposition of Ag thin films. The agreement includes simulation of the decreasing stress relaxation rate observed during deposition at increasing temperatures. © 2000 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
81.15.Aa Theory and models of film growth
02.70.Dh Finite-element and Galerkin methods
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Energy of an array of dislocations in a strained epitaxial layer deposited on a finite substrate

Shing-Dar Wang

J. Appl. Phys. 88, 7089 (2000); http://dx.doi.org/10.1063/1.1325376 (6 pages) | Cited 7 times

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By adopting the superposition principle and Fourier integral methodology, this work studies the energy of a dislocation array in a strained epitaxial layer deposited on a finite substrate with the same elastic constants. The total energy comprises the self-energy of the dislocations, the strain energy arising from the lattice mismatch, and the interaction energy between the dislocations and the mismatch. The sum of the self-energy and the interaction energy constitute the dislocation formation energy. Zero formation energy is used as the criterion to determine the epilayer critical thickness hc. No dislocation can appear when the epilayer thickness is below hc. When the epilayer thickness equals the critical thickness and the dislocation density is extremely low, the total energy is independent of the dislocation spacing p. If the critical thickness is less than the substrate thickness and the epilayer thickness is greater than the critical thickness, the total energy has a local minimum at dislocation spacing p=pmin; in addition, the corresponding dislocation density is the critical dislocation density. When p>pmin, the total energy decreases by decreasing the dislocation spacing, i.e., increasing the dislocation density. The total energy curve near p=pmin changes to a steep valley when the epilayer’s thickness approaches that of the substrate thickness. This corresponds to the experimental observation that a fast relaxation of misfit strain occurs when the epilayer thickness grows to a sufficient thickness. If p<pmin, the total energy markedly increases by decreasing the dislocation spacing. This phenomenon implies that work hardening is inevitable due to the dislocation–dislocation core interaction. © 2000 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Lk Linear defects: dislocations, disclinations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Carbon nitride thin film synthesized on iron buffer layers

Y. F. Lu, Z. F. He, Z. H. Mai, and Z. M. Ren

J. Appl. Phys. 88, 7095 (2000); http://dx.doi.org/10.1063/1.1323750 (4 pages) | Cited 3 times

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Carbon nitride thin films were deposited on iron buffer layers by pulsed laser deposition assisted with ion implantation. Two types of samples (A) and (B) were prepared with and without iron layers. Several techniques were used to study the properties of the samples. Scanning tunneling microscopy (STM) was used to observe the surface structures of the samples. The difference in their surface morphologies was studied. The STM measurements also provided the relation between tunneling current and bias voltage to study the local density of states of the sample surface by calculating (dI/dV)/(I/V). Three band edges were observed from the calculated curve. Measurements by Raman and Fourier transform infrared (FTIR) spectra were carried out to study the electronic properties of the samples. The Raman spectra showed the presence of triply bonded carbon nitride bonds (C�N) in sample (A), while only single bonds were observed in sample (B) by FTIR spectra. The mechanical properties were studied by nanoindentation. Both hardness and bulk modulus of the thin films were measured. © 2000 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
78.66.Nk Insulators
61.72.up Other materials
61.80.Jh Ion radiation effects
61.82.Ms Insulators
78.30.Hv Other nonmetallic inorganics
71.20.Ps Other inorganic compounds
68.35.B- Structure of clean surfaces (and surface reconstruction)
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

Nanoscale composition analysis of atomically flat SrTiO3(001) by friction force microscopy

Koichiro Iwahori, Shunji Watanabe, Maki Kawai, Keisuke Mizuno, Kenji Sasaki, and Mamoru Yoshimoto

J. Appl. Phys. 88, 7099 (2000); http://dx.doi.org/10.1063/1.1328065 (5 pages) | Cited 20 times

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Friction force microscopy (FFM) was used to distinguish the different surface terminations on the nanoscale on atomically flat SrTiO3(001) surfaces, obtained by a combination of ultrasonic agitation and subsequent annealing in air at 1000 °C. The surface exhibits atomically flat terraces and sharp steps whose height is 0.2 nm, corresponding to half the height of a unit cell of SrTiO3, or a single atomic layer, where strong friction contrast appears. A compositional analysis of the topmost surface by coaxial-impact-collision ion-scattering spectroscopy (CAICISS) indicated that the friction contrast corresponded to different surface terminations, namely, the SrO and TiO2 layer as a topmost surface, where the TiO2 domain was dominant. This is further supported by the correlation between the compositional Sr/Ti ratio and the area ratio which was observed by CAICISS and FFM, respectively. © 2000 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
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
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Empirical molecular dynamic study of SiC(0001) surface reconstructions and bonded interfaces

C. Koitzsch, D. Conrad, K. Scheerschmidt, and U. Gösele

J. Appl. Phys. 88, 7104 (2000); http://dx.doi.org/10.1063/1.1328783 (6 pages) | Cited 5 times

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Empirical molecular dynamics simulations based on the Tersoff potential are carried out for SiC(0001) surfaces and bonded interfaces. It is demonstrated that such a classical interatomic potential is able to correctly describe SiC-4H (0001)3×3 and math×mathR30° surface reconstructions. The surprising accuracy of the empirical simulations compared to results of density functional methods as well as experiments is demonstrated not only by obtaining reasonable structural parameters, but also by the correct prediction of such intricate effects like buckling in the topmost carbon layer of the math×math surface and polymerization in the silicon wetting layer of the 3×3 reconstruction. Because of the established good applicability of the Tersoff potential the simulations are used to predict the formation of SiC interfaces to be generated by wafer bonding and so far experimentally unobserved. It is shown that the bond energy crucially depends on the local atomic structure at the interface. The resulting bond energies range from 0.56 up to 3.16 J/m2 depending on the initially prepared reconstruction and alignment of the surfaces. © 2000 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)

Effects of dry processing on the optical properties of GaN

R. Cheung, R. J. Reeves, S. A. Brown, E. van der Drift, and M. Kamp

J. Appl. Phys. 88, 7110 (2000); http://dx.doi.org/10.1063/1.1328780 (5 pages) | Cited 6 times

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Effects of dry processing on the band-edge, blue, and yellow luminescence behavior of GaN surfaces exposed to SF6 and Ar plasmas have been investigated. Our results indicate that a higher concentration of donor-related defects are introduced on the top 100 nm GaN surface after Ar compared to SF6 plasma treatment. The higher defect concentration can be correlated to the yellow luminescence. In particular, the sample exposed to Ar plasma exhibits a factor of 20 increase in yellow luminescence intensity compared to the unetched sample. This effect is attributed to the introduction of defects—metastable states on the GaN surface after ion bombardment. Using a laser beam in the ultraviolet region, we have been able to write to and read from regions on the Ar-bombarded GaN surface. We demonstrate that the presence of reactive ion etch-induced metastable defects is central to the observed enhanced optical memory effect. The metastable states are identified as nitrogen deficient surfaces limited to the top few monolayers, as well as unidentified defect propagation down to 100 nm from the etched surface. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning

Temperature dependence analysis of the thermo-optic effect in silicon by single and double oscillator models

Francesco G. Della Corte, Maurizio Esposito Montefusco, Luigi Moretti, Ivo Rendina, and Giuseppe Cocorullo

J. Appl. Phys. 88, 7115 (2000); http://dx.doi.org/10.1063/1.1328062 (5 pages) | Cited 20 times

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The thermo-optic coefficient (dn/dT) of crystalline silicon has been critically analyzed in the temperature range 300–600 K, at the fiber optic communication wavelength of 1.5 μm. The temperature dependence has been attributed to the variation of the interband transition energies at some critical points of the silicon band structure. The experimental data have been fitted using single and double oscillator models. In particular, the double oscillator model, which is physically correlated to the silicon band structure, has been exploited to extrapolate the temperature dependence of the interband transition energies at some points (critical points) of the combined density of states. The extracted parameters are in good agreement with the data reported in the literature. Finally, in connection with both of the oscillator approximations, an analysis based on thermodynamic considerations is carried out, and electron–hole formation entropy and specific heat are calculated. The consistency of the obtained results validate the reliability of the proposed analysis. © 2000 American Institute of Physics.
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71.20.Mq Elemental semiconductors
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.40.Fy Semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Broad spectral sensitization of organic photovoltaic heterojunction device by perylene and C60

W. Feng, A. Fujii, S. Lee, H. Wu, and K. Yoshino

J. Appl. Phys. 88, 7120 (2000); http://dx.doi.org/10.1063/1.1323514 (4 pages) | Cited 12 times

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The characteristics of heterojunction devices consisting of indium-tin-oxide (ITO)/poly(3-alkylthiophene) (PAT)/N,N′-diphenyl glyoxaline-3, 4, 9, 10-perylene tetracarboxylic acid diacidamide (PV)/Al, ITO/PAT-PV/PV/Al, and ITO/PAT-PV-C60/PV/Al, which are typical photoinduced rectifiers, are reported. The device under dark conditions is almost insulating; however, when exposed to light marked rectification and strong photoresponse over a broad spectral range covering near-infrared to visible and UV wavelengths are observed. The effect of PV and C60 doping as well as annealing on spectral photoresponse and photoelectric conversion was investigated. The results show that the efficient photoinduced electron transfer from PAT to PV and C60 occurs at the interface between the composite and junction. © 2000 American Institute of Physics.
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85.60.-q Optoelectronic devices
61.72.Cc Kinetics of defect formation and annealing

Photoluminescence stability of a cyanoterphenyl chromophore in liquid crystalline polymeric systems

C. Sánchez, R. Alcalá, R. Cases, L. Oriol, and M. Piñol

J. Appl. Phys. 88, 7124 (2000); http://dx.doi.org/10.1063/1.1323518 (5 pages) | Cited 5 times

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Polarized photoluminescence as well as birefringence measurements have been performed in different films of side-chain liquid crystal polyacrylates prepared by in situ photopolymerization. The polymeric systems contain a cyanoterphenyl chromophore covalently bound as a side group. The stability of the luminescence has been studied as a function of the composition and crosslinking of the polymer films. Although both the thermal quenching and the optical bleaching of the luminescence depend on the composition of the polymer matrix they seem to be independent of the crosslinking degree. Polymer films showing a stable luminescence with a high dichroic ratio have been obtained in copolymers combining mono and diacrylates having the same mesogenic core, with a low content (10%) of the diacrylate (crosslinking agent). © 2000 American Institute of Physics.
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78.55.Bq Liquids
61.25.H- Macromolecular and polymers solutions; polymer melts
61.30.-v Liquid crystals
82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry
78.20.Fm Birefringence
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