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15 Apr 2000

Volume 87, Issue 8, pp. 3593-4041

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Lattice relaxation and metastability of the EL2 defect in semi-insulating GaAs and low temperature GaAs

G. Kowalski, S. P. Collins, and M. Moore

J. Appl. Phys. 87, 3663 (2000); http://dx.doi.org/10.1063/1.372396 (6 pages) | Cited 6 times

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Using the two-dimensional reciprocal space mapping, we have clearly established the relative positions of the arsenic atom (EL2 defect) corresponding to its stable and metastable configurations. It is shown that lowering only the temperature of the sample, before transition, induces transformation of the lattice. Characteristic temperature (120–140 K) below which such transformation takes place is the same as for thermal recovery of the defect. It is suggested that this temperature related lattice relaxation might promote a further transition to the metastable state. Full reciprocal space maps of the x-ray diffracted intensity are shown for the whole substrate-layer system. © 2000 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.72.-y Defects and impurities in crystals; microstructure

Evidence for the effect of carbon on oxygen precipitation in Czochralski silicon crystal

Peidong Liu, Xiangyang Ma, Jinxin Zhang, Liben Li, and Duanlin Que

J. Appl. Phys. 87, 3669 (2000); http://dx.doi.org/10.1063/1.372397 (5 pages) | Cited 10 times

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This article reports some new experimental evidence for the effect of carbon on oxygen precipitation in a high carbon content Czochralski silicon (H[C] Cz-Si) crystal. The oxygen precipitation occurring at an intermediate temperature of 950 °C has been especially investigated. In such case, the carbon atoms slightly participate in oxygen precipitation with 1200 °C preannealing, while the carbon atoms actively participate in oxygen precipitation with low temperature preannealing. The experiments show that the 1230 cm−1 absorption band in the Fourier transmission infrared spectrum definitely originates from the oxygen precipitates involving insignificant carbon reduction; on the other hand, the oxygen precipitates involving significant carbon reduction are surely irrelevant to the 1230 cm−1 absorption band. According to the correlation of the change in oxygen and carbon concentrations during oxygen precipitation, it is plausible that there is a critical precipitate size which distinguishes the carbon behavior in oxygen precipitation, that is, the carbon atoms actively participate in oxygen precipitation when the precipitates are smaller than the critical size; whereas, the carbon atoms are only slightly involved in oxygen precipitation when the precipitates are larger than the critical size. © 2000 American Institute of Physics.
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78.30.Am Elemental semiconductors and insulators
64.75.-g Phase equilibria
61.72.Cc Kinetics of defect formation and annealing
81.10.Fq Growth from melts; zone melting and refining

Defects in neutron transmutation doped silicon studied by positron annihilation lifetime measurements

M. Coeck, N. Balcaen, T. Van Hoecke, B. Van Waeyenberge, D. Segers, C. Dauwe, and C. Laermans

J. Appl. Phys. 87, 3674 (2000); http://dx.doi.org/10.1063/1.372398 (4 pages) | Cited 2 times

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Neutron transmutation doping of n-type silicon was obtained by irradiating the samples with thermal neutrons in order to create P atoms. Positron lifetime measurements were carried out and the evolution of the induced defects was studied by thermal annealing of the samples. The annealing out of the divacancy was seen between 200 and 350 °C. Around 700 °C large vacancy clusters (containing about eight vacancies) are formed. All the defects are annealed above 800 °C. © 2000 American Institute of Physics.
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61.80.Hg Neutron radiation effects
61.82.Fk Semiconductors
81.05.Cy Elemental semiconductors
61.72.J- Point defects and defect clusters
61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology
78.70.Bj Positron annihilation
61.72.Cc Kinetics of defect formation and annealing

Longitudinal and lateral stress measurements in shock-loaded gabbro and granite

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

J. Appl. Phys. 87, 3678 (2000); http://dx.doi.org/10.1063/1.372399 (5 pages) | Cited 2 times

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Plate impact experiments have been performed on two igneous rocks of different grain size. Shock stresses have been measured using embedded manganin stress gauges, up to ∼12 GPa. In the coarser grained material data was obtained by impacting rock flyer plates onto previously characterized targets. Results are compared and contrasted to the existing data for other geological materials. In the finer-grained material lateral stress was also measured. In combination with the longitudinal stresses, these results have been used to obtain the materials shear strength under shock loading conditions. Results suggest that the material is deforming in an inelastic manner. © 2000 American Institute of Physics.
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91.30.Nw Tsunamis
91.35.Gf Structure of the crust and upper mantle
62.50.-p High-pressure effects in solids and liquids
46.55.+d Tribology and mechanical contacts

CuInSe2 phase formation during Cu2Se/In2Se3 interdiffusion reaction

J. S. Park, Z. Dong, Sungtae Kim, and J. H. Perepezko

J. Appl. Phys. 87, 3683 (2000); http://dx.doi.org/10.1063/1.372400 (8 pages) | Cited 28 times

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Diffusion couples based upon Cu2Se/In2Se3 pairings have been examined in order to identify the kinetics of intermediate phase development and the associated phase equilibria. For the diffusion couples annealed at 550 °C for 1.5 h, all phases included in the Cu2Se–In2Se3 pseudobinary phase diagram section developed including the CuInSe2 (CIS) phase. Also, the In6Se7 phase formed for annealing times in excess of 1.5 h at 550 °C, indicating a modification of the diffusion pathway outside the pseudobinary phase diagram section. The growth of the CIS phase formed by reactive diffusion follows parabolic kinetics (x2=kt) with the k value of 3.3×10−8 cm2/s. CIS phase precipitates with a dendritic morphology are also produced within the Cu2Se side of the diffusion couple far from the initial interface, indicating that In is the fast component during interdiffusion. Based upon electron diffraction analysis and simulation of electron diffraction patterns, the dendritic shaped CIS precipitate structure was uniquely determined to be the metastable zinc blende type rather than the stable chalcopyrite-type structure. The structure and orientation relationship between the metastable CIS phase and the Cu2Se matrix satisfy the conditions established for the development of a solid state dendritic morphology. © 2000 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing
64.70.-p Specific phase transitions
64.75.-g Phase equilibria

A study of effect of cyanine dyes on ionic conductivity of AgBr grains

Hideo Furuuchi and Tadaaki Tani

J. Appl. Phys. 87, 3691 (2000); http://dx.doi.org/10.1063/1.372401 (5 pages) | Cited 1 time

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(1) On adsorption to cubic AgBr grains, both a 9-methyl-thiacarbocyanine (dye 1) and a 5,5′-dichloro-9-ethyl-thiacarbocyanine (dye 2), increased the conductivity of the grains with interstitial silver ions as carriers, repelling silver ions at the surface kink sites into interstitial positions. (2) On adsorption to octahedral AgBr grains, both dyes 1 and 2 increased the conductivity of the grains with mobile silver ions on the surface as carriers, whereas neither dyes 1 nor 2 increased the conductivity of the grains with interstitial silver ions as carriers. It is considered that the dye molecules repelled silver ions at surface sites, not into interstitial positions, but into surface sites where silver ions are mobile. (3) Dye 1 was preferably adsorbed to (100) faces on the surface of tetradecahedral AgBr grains, increasing the conductivity of the grains with interstitial silver ions as carriers, and was then adsorbed to the (111) faces after the saturation of the (100) faces by the dye, giving little influence on the ionic conductivity. On the contrary, dye 2 was preferably adsorbed to the (111) faces, giving little influence on the conductivity, and was then adsorbed to the (100) faces after the saturation of the (111) faces by the dye, increasing the conductivity. This result provided a method to examine the kind of faces on the surface of silver halide grains. (4) The observation of preferential adsorption on different crystal faces was successfully used to prove the presence of (100) faces on the side surfaces of a twinned tabular grain. © 2000 American Institute of Physics.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
61.72.J- Point defects and defect clusters
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Effects of donor concentration on transient enhanced diffusion of boron in silicon

S. Solmi and M. Bersani

J. Appl. Phys. 87, 3696 (2000); http://dx.doi.org/10.1063/1.372402 (4 pages) | Cited 7 times

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The effects of substrate donor concentration on transient enhanced diffusion (TED) of boron implanted into silicon wafers predoped with arsenic or phosphorus have been investigated by using secondary ion mass spectroscopy and theoretical simulations. Boron ions have been implanted at low energy (10–20 keV) and successively annealed in the temperature range 700–1000 °C. No detectable boron TED (TED<10×) has been observed in samples uniformly predoped with P at the concentration of 1.2×1020 cm−3. The B TED is strongly reduced even in the samples predoped with As. However, for the highest As concentration (1.3×1020 cm−3) an exponential high diffusivity tail has been detected in the B profiles at all the examined annealing temperatures. This anomalous effect has been attributed to the interstitials produced by an As clustering reaction occurring during the low temperature annealing. The main effects responsible for the vanishing of the B TED, i.e., ionization of the interstitials (Fermi level effect), competitive behavior of P in the interaction with the interstitials, and donor-acceptor pairing have been examined and discussed. © 2000 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.J- Point defects and defect clusters

Low-temperature formation of Si(001) 2×1 surfaces from wet chemical cleaning in NH4F solution

Vinh Le Thanh, D. Bouchier, and G. Hincelin

J. Appl. Phys. 87, 3700 (2000); http://dx.doi.org/10.1063/1.372403 (7 pages) | Cited 21 times

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In situ reflection high-energy electron diffraction and thermal desorption spectroscopy were used to investigate the surface structure and chemistry of Si(001) surfaces after wet chemical etching in dilute HF and ammonium fluoride (NH4F) solutions. The HF-etched surfaces were found to be rough and terminated by mono-, di-, and tri-hydride species, in good agreement with previous vibrational spectroscopy measurements. The surface roughness observed after HF treatment appears to arise from surface defects such as adstructures and kinks left on the surface after the removal of the oxide layers. The Si(001) etching processes in NH4F solution were found to be highly anisotropic, and the etching time in the solution was found to be the key parameter which determined the chemistry and the morphology of the surface. We show that for a limited etching time (∼1 min), a flat and bulk-like dihydride-terminated Si(001) surface could be formed and this surface was found to transform, upon annealing in ultrahigh vacuum, into a well-developed 2×1 reconstruction at a temperature as low as ∼400 °C. Our results also suggested that (111) microfacets were formed on Si(001) surfaces only after a prolonged etching in NH4F solution and they remained stable up to an annealing temperature of ∼650 °C. © 2000 American Institute of Physics.
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81.05.Cy Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
81.65.Cf Surface cleaning, etching, patterning
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Dependence of crystallinity on oxygen pressure and growth mode of La0.3Sr1.7AlTaO6 thin films on different substrates

Yijie Li, X. J. Wu, J. G. Wen, Y. Takahashi, and K. Tanabe

J. Appl. Phys. 87, 3707 (2000); http://dx.doi.org/10.1063/1.372404 (4 pages) | Cited 1 time

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The influence of oxygen pressure on epitaxial quality of La0.3Sr1.7AlTaO6 (LSAT) films deposited by laser ablation on SrTiO3(100), LaAlO3(100), and MgO(100) substrates has been investigated. X-ray diffraction shows only (00l) peaks in the oxygen pressure range from 10−3 to 500 mTorr. However, the crystallinity of LSAT films is found to be sensitive to oxygen pressure and dependent on substrates. LSAT films on SrTiO3 have the narrowest full width at half maximum (FWHM) of 0.05° at 300 mTorr. The films on LaAlO3 exhibit a FWHM of 0.3° at 50–100 mTorr. On MgO substrate, significant improvement of crystallinity is achieved at 200–300 mTorr, but rocking curves give an FWHM of 0.70°–1.00° due to the large lattice mismatch between LSAT and MgO. Atomic force microscopy analyses demonstrate smooth LSAT surfaces without identified grains. Reflection high-energy electron diffraction studies suggest a two-dimensional growth mode for LSAT films on SrTiO3 and LaAlO3 and a three-dimensional growth mode for LSAT films on MgO. Cross-sectional high-resolution electron micrographs indicate that LSAT films on SrTiO3 and LaAlO3 have defect-free epitaxial structure and atomically flat interfaces. An 80 Å thick intermediate layer with partially disordering is observed between LSAT films and MgO substrates. © 2000 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)

Strain and photoluminescence characterization of cubic (In,Ga)N films grown on GaAs(001) substrates

X. L. Sun, Y. T. Wang, Hui Yang, L. X. Zheng, D. P. Xu, J. B. Li, and Z. G. Wang

J. Appl. Phys. 87, 3711 (2000); http://dx.doi.org/10.1063/1.372405 (4 pages) | Cited 3 times

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Cubic InxGa1−xN films were successfully grown on GaAs(001) substrates by metalorganic chemical-vapor deposition. The values of x content ranging from 0.10 to 0.24 obtained at different growth conditions were measured by double-crystal x-ray diffraction (XRD). The perpendicular and parallel elastic strain of the In0.2Ga0.8N layer, ϵ⊥=0.4% and ϵ∥=−0.4% for GaN and ϵ⊥=0.37% and ϵ∥=−0.37% for InGaN, respectively, were derived using the XRD measurements. The inhomogeneous strain and the average grain size of the In0.2Ga0.8N/GaN films were also studied by XRD. Photoluminescence spectra were used to measure the optical characterization of the InxGa1−xN thin films with different In composition, and the near-band-edge emission dependence of cubic InxGa1−xN on the x value is nearly linear with In content x⩽0.24. © 2000 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Fd III-V semiconductors
68.60.Bs Mechanical and acoustical properties
78.55.Cr III-V semiconductors
62.20.F- Deformation and plasticity

Thermal stability and breakdown strength of carbon-doped SiO2:F films prepared by plasma-enhanced chemical vapor deposition method

J. Lubguban, Y. Kurata, T. Inokuma, and S. Hasegawa

J. Appl. Phys. 87, 3715 (2000); http://dx.doi.org/10.1063/1.372406 (8 pages) | Cited 6 times

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Carbon-doped SiO2:F films were deposited by changing the CH4 flow rate, [CH4], using a plasma-enhanced chemical vapor deposition technique from SiH4/O2/CF4/CH4 mixtures. The thermal stability for the films deposited with a fixed temperature of 300 °C was investigated through the changes in the dielectric constant (ϵS), IR spectra and stress with annealing temperature, TA, from 400 to 800 °C. The breakdown strength for films as-deposited were also measured. The addition of carbon to SiO2:F films resulted in the films with low ϵS (up to 3.0) and high water resistivity. Addition of high [CH4] in the films resulted in stable ϵS for TA=500 °C or less. The CH4 addition initially decreased the breakdown strength but then increases again. Under the application of sum rule to the analysis of the vibrational absorption, it was suggested that the decrease in ϵS with [CH4] results from the decrease in the effective dynamic charge of Si–O dipoles along with the direct contribution of Si–F bonds incorporated to SiO2. The decrease in Si–F and Si–O peak frequencies based on the analysis of the charge transfer model suggested an increase in the Si–F and Si–O bond length, in addition to a decrease in the Si–O–Si bond angle. © 2000 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.55.-a Thin film structure and morphology
73.61.Ng Insulators
77.22.Jp Dielectric breakdown and space-charge effects
77.22.Ch Permittivity (dielectric function)
78.30.Hv Other nonmetallic inorganics
63.20.-e Phonons in crystal lattices
78.66.Nk Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

The field-induced cholesteric-nematic phase transition and its dependence on layer thickness, boundary conditions, and temperature

Luc J. M. Schlangen, Alexandre Pashai, and Hugo J. Cornelissen

J. Appl. Phys. 87, 3723 (2000); http://dx.doi.org/10.1063/1.372407 (7 pages) | Cited 7 times

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Chiral-nematic liquid-crystal layers which have a short pitch, homeotropic boundary conditions, and bistable properties are investigated with respect to the temperature dependence of their field-induced cholesteric-nematic phase transition. Hereto the threshold field needed for the transition is studied as a function of the layer thickness. This is done for various temperatures. The threshold field hardly depends on the layer thickness. Moreover, it sharply rises below −5 °C. Both the value of the threshold field and its temperature dependence can be fully described in terms of liquid-crystal bulk material parameters, the conditions at the homeotropic boundary layer used do not play a role. From the threshold field data the twist elastic constant is determined as a function of temperature. This temperature dependence is compared to the temperature dependence as determined from the square of the long range order parameter calculated from temperature dependent refractive index data. A good correlation is found between both data sets of the twist elastic constant. © 2000 American Institute of Physics.
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64.70.M- Transitions in liquid crystals
42.70.Df Liquid crystals
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
62.20.D- Elasticity

Surfactant controlled growth of GaInP by organometallic vapor phase epitaxy

R. T. Lee, J. K. Shurtleff, C. M. Fetzer, G. B. Stringfellow, S. Lee, and T. Y. Seong

J. Appl. Phys. 87, 3730 (2000); http://dx.doi.org/10.1063/1.372408 (6 pages) | Cited 9 times

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The effect of the surfactant Sb has been studied for GaInP semiconductor alloys grown by organometallic vapor phase epitaxy. Dramatic changes in the optical and electrical properties of GaInP with CuPt ordering have been observed. A small concentration of triethylantimony (TESb) in the vapor is found to cause Sb to accumulate at the surface. In situ surface photoabsorption analysis indicates that Sb changes the surface bonding by replacing the [math10] P dimers that are responsible for the formation of the CuPt structure during growth with [math10] Sb dimers. As a result, the degree of order for the GaInP layers is decreased, as shown by transmission electron diffraction studies. The 20 K photoluminescence spectra show a 131 meV peak energy increase for GaInP layers grown on vicinal substrates when a small amount of Sb [Sb/P(v)=4×10−4] is added to the system during growth. The use of surfactants to control specific properties of materials is expected to be a powerful tool for producing complex structures. In this article, the growth of heterostructures by modulating the Sb concentration in the vapor is demonstrated. © 2000 American Institute of Physics.
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81.05.Dz II-VI semiconductors
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Structure and interface-controlled growth kinetics of ZnAl2O4 formed at the (11math0) ZnO/(01math2) Al2O3 interface

C. R. Gorla, W. E. Mayo, S. Liang, and Y. Lu

J. Appl. Phys. 87, 3736 (2000); http://dx.doi.org/10.1063/1.372454 (8 pages) | Cited 28 times

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The solid state reaction between metalorganic chemical vapor deposition grown epitaxial ZnO films and the R-plane sapphire substrate after annealing at 1000 °C for various times in an O2/N2 atmosphere was studied in detail. Multiple epitaxial relationships between the reaction product (ZnAl2O4) and the reactants were observed, as determined by cross-sectional transmission electron microscopy. In the dominant epitaxial relationship (A1), the (2math0) plane of ZnAl2O4 was parallel to the (math101) plane of Al2O3. A twin (A2) of orientation A1, i.e. (2math0) ZnAl2O4//(10math1) Al2O3, and a closely related orientation (B) wherein the (2math0) ZnAl2O4 plane is parallel to the (math2math0) ZnO plane (which is equivalent to a 5° clockwise rotation about the [mathmath2] ZnAl2O4 or [0001] ZnO zone axis relative to A2), were also observed. Enhanced growth was observed at grain boundaries. It was necessary to measure the spinel growth rate from grains with the same orientation far away from grain boundaries because the growth rate was observed to be influenced by the orientation of the grains in addition to the enhanced growth at grain boundaries. The growth rate was observed to follow a linear rate law during early stages (for grains with orientation A1), suggesting an interface-controlled reaction. The structures of the ZnO/Al2O3, ZnO/ZnAl2O4 and ZnAl2O4/Al2O3 interfaces were studied for grains with this orientation (A1). The 13.7% lattice mismatch between ZnO and ZnAl2O4 was relieved by a series of misfit dislocations spaced five to six (1math00) ZnO planes apart. Due to the small lattice misfit (2.1%) at the ZnAl2O4/Al2O3 interface, very few misfit dislocations were present. This interface was faceted and the sapphire surface had a series of single steps. It is expected that the reaction at the ZnAl2O4/ZnO interface is the rate-controlling step due to the necessity for a dislocation climb (of a large number of misfit dislocations) for movement of this interface. © 2000 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
81.05.Dz II-VI semiconductors
68.35.Ct Interface structure and roughness
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.40.Gh Other heat and thermomechanical treatments
61.72.Mm Grain and twin boundaries
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.Nq Composition and phase identification
82.20.Pm Rate constants, reaction cross sections, and activation energies

Strain and shape analysis of multilayer surface gratings by coplanar and by grazing-incidence x-ray diffraction

T. Baumbach, D. Lübbert, and M. Gailhanou

J. Appl. Phys. 87, 3744 (2000); http://dx.doi.org/10.1063/1.372409 (15 pages) | Cited 11 times

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The surface shape and the spatial distribution of strain in GaInAs/InP multilayer gratings is experimentally determined by combining high-resolution x-ray diffraction and grazing-incidence diffraction. Dramatic deformations of the diffraction patterns in the measured reciprocal space maps of such gratings indicate a strongly nonuniform character of lattice distortions in the layers, caused by elastic strain relaxation. By coupling x-ray diffraction theory and elasticity theory within one single evaluation formalism, an experimental strain and shape analysis could be performed which was not yet available in this form by other methods. The different components of the strain tensor are determined by recording diffraction patterns around different reciprocal lattice points. We study how the strain relaxation of the multilayer grating evolves towards the free surface, and how the local strain distribution is modulated due to the compositional profile of the layered setup. Furthermore, the article describes in detail the effects of the grating shape, the multilayer morphology, and the lattice strain field on the diffraction patterns of multilayered gratings. © 2000 American Institute of Physics.
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42.79.Dj Gratings
68.60.Bs Mechanical and acoustical properties
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Effect of coating thickness on thermal stresses in tungsten-coated optical fibers

Sham-Tsong Shiue, Pin-Tzu Lien, and J.-L. He

J. Appl. Phys. 87, 3759 (2000); http://dx.doi.org/10.1063/1.372410 (4 pages) | Cited 12 times

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This study investigates the effect of coating thickness on the thermal stresses in tungsten-coated optical fibers. Theoretical results indicate that the maximum normal stress in the tungsten coating decreases with increasing coating thickness. However, the maximum shear stress at the interface of the glass fiber and tungsten coating increases. Eight samples of tungsten-coated optical fibers with coating thicknesses of 58, 75, 101, 128, 158, 383, 557, and 1013 nm, respectively, are immersed in liquid nitrogen for one day. Experimental results show that thermal stresses will either break or delaminate the tungsten coating. The crack density decreases with increased coating thickness, while the delaminated area of tungsten coating increases. The theoretical results can explain the break and delamination of the tungsten coating in the optical fiber. To minimize the break and delamination of the tungsten coatings in the optical fibers, the optimal thickness of the tungsten coating is about 158 nm. © 2000 American Institute of Physics.
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42.81.Bm Fabrication, cladding, and splicing
68.60.Bs Mechanical and acoustical properties
68.60.Dv Thermal stability; thermal effects
68.55.-a Thin film structure and morphology
81.05.Bx Metals, semimetals, and alloys
65.40.De Thermal expansion; thermomechanical effects

Surface superstructure on fullerenes annealed at elevated temperatures

B. An, S. Fukuyama, K. Yokogawa, M. Yoshimura, Y. Korai, and I. Mochida

J. Appl. Phys. 87, 3763 (2000); http://dx.doi.org/10.1063/1.372411 (5 pages) | Cited 2 times

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Scanning tunneling microscopy images of fullerenes annealed at elevated temperatures are investigated. Three types of ringlike superstructures of (√×√)R30° of graphite, the circular type, the U type, and the semicircular type, are observed on the curved surface of the fullerenes annealed in the temperature range from 2073 to 2673 K. A new modified interference model, in which both the α and β site atoms contribute to the tunneling current caused by the curved surface, is proposed. The model well simulates the three types of the ringlike superstructure of graphite and the continuous change from the triangular structure of graphite to the ringlike superstructure of graphite. © 2000 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
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

Observations of reaction zones at chromium/oxide glass interfaces

Nan Jiang and John Silcox

J. Appl. Phys. 87, 3768 (2000); http://dx.doi.org/10.1063/1.372412 (9 pages) | Cited 10 times

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Cr is often used in thin metallic film structures on oxide glasses since it exhibits good adhesion. The most likely explanation of the basic adhesion mechanism is the formation of a graded metal oxide layer at the interface. In general, details of the interface properties are needed to get a complete understanding of phenomena such as adhesion. We report here observations of interface structures using spatially resolved electron energy loss spectrometry with a small probe (2 Å) scanning transmission electron microscope. Two interfaces, evaporated Cr/alkaline earth boroaluminosilicate glass and sputtered Cr/barium boroaluminosilicate glass, are examined. As expected from the classical adhesion theory, very thin partially oxidized intermediate layers are seen in both samples. However, a 5 nm Cr diffusion layer is also found in the evaporated Cr/glass system (without heat treatment), but it appears absent in the sputtered Cr glass system (with heat treatment). This difference suggests that the mechanisms of the adhesion of Cr to oxide glass are dependent on interface history. © 2000 American Institute of Physics.
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68.35.Ct Interface structure and roughness
79.20.Kz Other electron-impact emission phenomena
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
81.65.Mq Oxidation

Interdiffusion mechanisms in CdTe/CdMgZnTe:N modulation-doped heterostructures

A. Arnoult, J. Cibert, S. Tatarenko, and A. Wasiela

J. Appl. Phys. 87, 3777 (2000); http://dx.doi.org/10.1063/1.372413 (8 pages) | Cited 6 times

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p-type modulation doping of CdTe–CdMgZnTe heterostructures, using nitrogen as a dopant, induces a strong interdiffusion of the quantum wells. Photoluminescence, secondary ion mass spectrometry, and x-ray diffraction measurements give a coherent description of the interdiffusion process: the destruction of the quantum wells occurs essentially by exchange of Cd and Mg atoms across the interface, while the Zn atoms stay in their lattice sites. We show that the presence of nitrogen at the interface, which enhances the interdiffusion, is related to the diffusion of nitrogen and not to segregation. Additional mechanisms are observed at higher doping. © 2000 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
81.05.Dz II-VI semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
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)
66.30.J- Diffusion of impurities

Superfocusing of surface polaritons in the conical structure

A. J. Babadjanyan, N. L. Margaryan, and Kh. V. Nerkararyan

J. Appl. Phys. 87, 3785 (2000); http://dx.doi.org/10.1063/1.372414 (4 pages) | Cited 79 times

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It is shown that at the propagation of a surface polariton through a pointed cone its wavelength decreases to zero as it approaches the edge of the cone. As a result, the polariton is focused in a very small region and the strengths of the wave fields anomalously increase. The phenomenon could be used for creation of a scanning near-field optical microscope to investigate the nanometer-scale surface areas. © 2000 American Institute of Physics.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.-r Electron states at surfaces and interfaces
07.79.Fc Near-field scanning optical microscopes
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

Field inhomogeneity effects on photoreflectance spectra of ZnSe/GaAs

J. H. Song, E. D. Sim, K. S. Baek, and S. K. Chang

J. Appl. Phys. 87, 3789 (2000); http://dx.doi.org/10.1063/1.372415 (4 pages) | Cited 4 times

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Photoreflectance measurements from ZnSe epilayers of different thicknesses were carried out. In photoreflectance spectra, the exciton line shape “rotation” is observed to be much slower than that in the reflectance spectra by increasing the epilayer thicknesses. To analyze the exciton line shape rotation quantitatively, the photoreflectance spectra were calculated considering the built-in electric field inhomogeneity effects near the interface as well as the interference effects. Calculated line shapes of the photoreflectance spectra show a good agreement with the observations. Our results imply that inhomogeneity effects of the interface built-in electric field plays an important role in the spectral rotation in photoreflectance. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.20.-e Optical properties of bulk materials and thin films
78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena

Photoluminescence of CuGaS2 epitaxial layers grown by metalorganic vapor phase epitaxy

Sho Shirakata and Shigefusa Chichibu

J. Appl. Phys. 87, 3793 (2000); http://dx.doi.org/10.1063/1.372416 (7 pages) | Cited 8 times

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High quality epitaxial layers of CuGaS2 have been grown on GaAs and GaP substrates by low-pressure metalorganic vapor phase epitaxy using cycropentadienylcoppertriethylphosphine, normal-tripropylgallium, and ditertiallybutyl sulphide precursors. Photoluminescence (PL) studies at 8 K have been carried out, and exciton-related PL peaks at 2.489 and 2.477 eV have been observed in addition to PL peaks at 2.43 (free-to-bound), 2.39 (donor-acceptor pair), and broad band at 1.65 eV. Temperature and excitation intensity dependences of the PL peaks have been studied in detail, and PL properties are compared with those for the bulk CuGaS2 crystals grown by the chemical vapor transport (CVT) method. PL spectra for nearly stoichiometric CuGaS2 epilayers exhibited the intense free exciton-related PL peak over the entire temperature range (8–300 K), which are in contrast to PLs dominated by defect-related deep peaks for Ga-rich or Cu-rich epilayers and the impurity related near-band edge PL for the CVT bulk crystal. These PL results show that the nearly stoichiometric CuGaS2 epilayers grown in this study are the highest quality reported so far. © 2000 American Institute of Physics.
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78.66.Li Other semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.55.Hx Other solid inorganic materials
71.55.Ht Other nonmetals

Photothermal ionization spectroscopy of shallow nitrogen donor states in 4H–SiC

C. Q. Chen, J. Zeman, F. Engelbrecht, C. Peppermüller, R. Helbig, Z. H. Chen, and G. Martinez

J. Appl. Phys. 87, 3800 (2000); http://dx.doi.org/10.1063/1.372417 (6 pages) | Cited 9 times

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Photothermal ionization spectroscopy (PTIS) measurements were carried out on a free-standing, high purity and high quality 4H–SiC epitaxial layer at various temperatures. The two step photothermal ionization process is clearly reflected in the temperature dependence of the photoconductivity. The PTI spectrum at a temperature of 25.6 K exhibits one order of magnitude higher energy resolution than the infrared absorption spectra of 4H–SiC bulk material. It reveals five strong, well resolved electronic transition lines associated with the shallow nitrogen donor. The ionization energy of the shallow nitrogen donor is deduced to be 60.2±0.5 meV based on experimental results. Furthermore, PTI magnetospectroscopy measurements were performed to investigate the symmetry properties of these transitions in Faraday configuration. No linear Zeeman splitting is observed, however, these lines show a diamagnetic shift. It indicates that the excited states of the shallow nitrogen donor are nondegenerate at zero magnetic field, which is consistent with the fact that the effective mass tensor of 4H–SiC has three different diagonal components. © 2000 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
78.66.Li Other semiconductors
78.30.Hv Other nonmetallic inorganics

Photoinduced optical second-harmonic generation of SiNO films deposited on Si〈111〉 substrate

K. Pluciński, I. V. Kityk, M. Makowska-Janusik, A. Mefleh, H. Kaddouri, and S. Benet

J. Appl. Phys. 87, 3806 (2000); http://dx.doi.org/10.1063/1.372418 (9 pages) | Cited 2 times

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Optical photoinduced second-harmonic generation (PISHG) of SiON films deposited on Si〈111〉 substrates has been studied. Nitrogen laser (λ=337 nm) was used as a source of pumping light. We have found that with an increase of photoinducing power and nitrogen-to-oxygen (N/O) ratio, the PISHG for probe YAG-Nd laser (for the doubled frequency λ=0.53 μm) signal increases and achieves its maximum value at photoinducing power about 0.96 GW/cm2. The maximal value of the PISHG was equal about 1 pm/V. With decreasing temperature, the PISHG signal strongly increases below 28 K. Femtosecond probe-pump measurements indicate the existence of the PISHG maximum at pump-probe time delay about 0.4 ps. We explain these dependencies within a framework of the quantum chemical approach and molecular dynamics interface structure optimization. Role of photoinduced anharmonic electron-phonon interaction is demonstrated. We have revealed that Si–N chemical bonds play a key role in the observed photoinduced nonlinear optics effect. © 2000 American Institute of Physics.
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78.66.Nk Insulators
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics
68.35.Ct Interface structure and roughness
61.50.Lt Crystal binding; cohesive energy

The optical and vibrational properties of the quaternary chalcopyrite semiconductor alloy AgxCu1−xGaS2

In-Hwan Choi, Sung-Hwan Eom, and P. Y. Yu

J. Appl. Phys. 87, 3815 (2000); http://dx.doi.org/10.1063/1.372419 (8 pages) | Cited 12 times

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The absorption, emission and Raman spectra of the quaternary chalcopyrite alloys AgxCu1−xGaS2 have been measured as a function of the Ag concentration. We find strong and highly nonlinear dependence on the alloy concentration in the optical band gap (a large bowing parameter). On the other hand, most of the Raman peaks exhibit either small energy shifts or large broadening with alloying. We conclude that the effect of substitution of the Ag cations by Cu in AgGaS2 on its band structure cannot be predicted by the simple virtual crystal potential approximation as a result of the large difference in electronegativity and bond length between Ag and Cu. © 2000 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
61.50.Lt Crystal binding; cohesive energy
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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