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1 May 2007

Volume 101, Issue 9, Articles (09xxxx)

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Fourier analysis applied on in situ laser reflectometry during III-nitride metal organic chemical vapor deposition growth

C. Simbrunner, H. Sitter, and A. Bonanni

J. Appl. Phys. 101, 093501 (2007); http://dx.doi.org/10.1063/1.2722247 (7 pages)

Online Publication Date: 1 May 2007

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In this article we present the Fourier analysis of kinetic reflectometry spectra acquired during metalorganic chemical vapor deposition. We can show that offset errors due to background radiation can be completely removed by the method itself without using filters or lock-in amplifiers. Additionally, calibration of the reflected intensity is needed as long as the response of the detector is linear to the reflected intensity of the sample. By analyzing the time dependent part of the signal growth rate, layer thickness and the refractive index of the growing layer can be deduced. We demonstrate that, by applying the method to the GaN:Mg δ-doping process, it is possible to obtain accurate information about the time, optical properties, and thickness of the grown multilayers with a resolution down to the monolayer range.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
68.65.Ac Multilayers

Defect reduction by periodic SiNx interlayers in gallium nitride grown on Si (111)

K. Y. Zang, Y. D. Wang, L. S. Wang, S. Y. Chow, and S. J. Chua

J. Appl. Phys. 101, 093502 (2007); http://dx.doi.org/10.1063/1.2724793 (4 pages) | Cited 3 times

Online Publication Date: 1 May 2007

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Periodic SiNx interlayers were employed during the metal-organic chemical vapor deposition of epitaxial GaN on AlN buffer layers grown on Si (111) substrates. The growth and the evolution of defects were studied in this paper. A reduction of the threading dislocation density to ∼ 109 cm−2 was observed on the surface of GaN by counting the surface pit density from the atomic force microscopy results. Besides the observation of the continuous bending and subsequent recombination of the threading dislocations related to the periodic conduction of the SiNx interlayer characterized using cross-sectional transmission electron microscopy, we observed a different behavior induced by the SiNx interlayers: Si-rich inverted hexagonal pyramids with their base on the (0001) plane and six sidewalls on the (10math1) plane were found near the top surface of the GaN film at the location of SiNx insertion layer characterized using electron energy loss spectroscopy. The preferential deposition of the SiNx on the sidewalls of the pit defects leads to the subsequently selective growth of the GaN beyond the pit defects, which leads to the burying of the pits and the reduction of the pit defects within the film due to the micromasking effect of the SiNx.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Photoluminescence and self-interference in germanium-doped silica films

Y. M. Yang, L. W. Yang, M. Q. Cai, and Paul K. Chu

J. Appl. Phys. 101, 093503 (2007); http://dx.doi.org/10.1063/1.2721784 (4 pages) | Cited 4 times

Online Publication Date: 2 May 2007

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Germanium-doped silica films were prepared by magnetron cosputtering and postannealing. The photoluminescence properties and their dependence on the Ge contents and annealing temperature were investigated. Our experiments indicate that the observed light emission originates from the neutral oxygen vacancy defects. The substructures in the luminescence bands of the films were found to result from multiple-beam interferences of the emission in the optical cavity formed by the transparent films.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments

Scaling of fracture energy in tensile debonding of viscoelastic films

Muralidhar Seshadri, Sunil Saigal, Anand Jagota, and Stephen J. Bennison

J. Appl. Phys. 101, 093504 (2007); http://dx.doi.org/10.1063/1.2717550 (8 pages) | Cited 2 times

Online Publication Date: 3 May 2007

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The work done to separate viscoelastic adherends is often dominated by energy dissipation due to the bulk deformation that accompanies the intrinsic processes of interfacial separation. The inter-relationship between bulk and interfacial deformation processes is studied here by analyzing a one-dimensional model for steady-state crack propagation between a rigid substrate and a thin viscoelastic film when the latter is subjected to tensile loading and the former is fixed. The viscoelastic layer is represented by a standard linear solid and is connected to the rigid substrate via a Dugdale cohesive zone model. The principal result of the analysis is a prediction for the dependence of the total work of fracture on the rate of loading. A threshold crack-tip velocity that governs the onset of dissipation is determined as a function of the film thickness and the interfacial and viscoelastic parameters of the film. Based on the ratio of the crack-tip velocity to the threshold velocity, three velocity regimes are identified where the energy dissipation is low, high, or intermediate. These correspond, respectively, to the overlap of the cohesive zone with the film material that is completely relaxed, is completely unrelaxed, or is in the process of relaxation. An approximate solution for the scaling of fracture energy in these three regimes has been presented. Finally, the relevance of these results to a two-dimensional problem is discussed.
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46.50.+a Fracture mechanics, fatigue and cracks
46.35.+z Viscoelasticity, plasticity, viscoplasticity
46.55.+d Tribology and mechanical contacts

Seeding method with silicon powder for the formation of silicon spheres in the drop method

Zhengxin Liu, Takehiko Nagai, Atsushi Masuda, Michio Kondo, Kazutoshi Sakai, and Koichi Asai

J. Appl. Phys. 101, 093505 (2007); http://dx.doi.org/10.1063/1.2718872 (5 pages) | Cited 6 times

Online Publication Date: 3 May 2007

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Silicon spheres with a size distribution around 1.0 mm diameter, which are applicable to spherical solar cells, were formed by dropping molten silicon through a nozzle in a free-fall tube, namely, the drop method. Here we show a seeding technique for the formation of silicon spheres. In this technique, pure silicon powders with a size distribution of 1−75 μm were ejected to the molten silicon droplets at a selected part of the free-fall tube using argon carrier gas. It was considered that the attached silicon powders on the droplets worked as nuclei and stimulated the solidification to occur at low undercooling from one place. Characterizations with scanning electron microscope, carrier lifetime, and photoluminescence measurements demonstrated that the crystallinity of silicon spheres were significant improved by the seeding method. The undercooling of molten silicon droplets at solidification was speculated to decrease from ∼ 250 °C to below 50 °C by seeding power ejection. This resulted in an increase of average minority carrier lifetime from <0.1 μs  to >1.0 μs.
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81.10.Fq Growth from melts; zone melting and refining
81.30.Fb Solidification
64.70.D- Solid-liquid transitions
78.55.Ap Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.66.Bi Elemental solids

Free carrier distribution profiling of 4H-SiC substrates using a commercial optical scanner

Joshua D. Caldwell, Orest J. Glembocki, Sharka M. Prokes, Evan R. Glaser, Karl D. Hobart, Darren M. Hansen, Gilyong Chung, Alexander V. Bolotnikov, and Tangali S. Sudarshan

J. Appl. Phys. 101, 093506 (2007); http://dx.doi.org/10.1063/1.2722251 (7 pages) | Cited 2 times

Online Publication Date: 3 May 2007

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Presented here is an explanation for the use of a commercial optical scanner for the mapping of doping density (ND) within SiC substrates and as a local probe for ND variations. This method provides a fast and cost effective method for determining ND homogeneity, examining local electrical characteristics, and recognizing defect sites including areas of different polytypes or polycrystallinity. Hall effect and micro-Raman spectroscopy were used to calibrate the transmission amplitude, integrated area and scanner red, green, blue (RGB) luminance values with ND. It is shown that features presented in the calculated ND maps strongly correlate to those observed in Lehighton resistivity maps.
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61.72.S- Impurities in crystals
72.20.My Galvanomagnetic and other magnetotransport effects
78.30.Hv Other nonmetallic inorganics

On the influence of loading profile upon the tensile failure of stainless steel

G. T. (Rusty) Gray, III, N. K. Bourne, and B. L. Henrie

J. Appl. Phys. 101, 093507 (2007); http://dx.doi.org/10.1063/1.2720099 (9 pages) | Cited 3 times

Online Publication Date: 3 May 2007

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A material placed in direct contact with a high explosive experiences a Taylor wave (triangular-shaped) shock loading profile. While a large number of studies have probed the structure, properties, and tensile response of materials subjected to square-topped shock loading pulses histories, few studies have systematically quantified the influence of shock-wave profile shape on material response. Samples of 316L stainless steel were shock loaded to peak stresses of 6.6, 10.2, and 14.5 GPa to examine the influence of square-topped and triangular (Taylor wave)-shaped pulse loading on the dynamic tensile behavior (spallation). The 316L SS samples were loaded with a square-topped pulse to each peak shock stress, using a pulse duration of 0.9 μs. They displayed increasing incipient spallation damage with increasing peak stress. Samples loaded to the peak shock stresses of 6.6 and 10.2 GPa with a Taylor-wave loading pulse (which immediately unloads the sample after the peak Hugoniot stress is achieved) exhibited no damage. Only the 14.5 GPa Taylor pulse shocked sample exhibited both a pull-back signal and incipient damage following tensile loading. The damage evolution in the square-topped shocked samples was found to be a mixture of void and strain localization damage, the void fraction increasing with peak shock amplitude. With the Taylor-wave loading profile of amplitude 14.5 GPa, a high incidence of shear localization and low incidence of void formation was observed. Detailed analysis of the damage evolution as a function of shock pulse shape revealed that a nominally equivalent level of incipient damage was obtained using a Taylor-wave or square-topped loading pulse when a similar rear sample surface stress-time total impulse was applied. In order to induce equivalent damage with the two pulse shapes, the impulse applied needed to be nominally matched. For this to occur, the Taylor-wave profile required twice the amplitude of the square one and the durations of each pulse needed to be appropriately scaled. Detailed metallographic, microtextural, and void shape and size analyses of the damage evolution are presented as a function of the inferred loading pulse shape and the peak Hugoniot stress.
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62.50.-p High-pressure effects in solids and liquids
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Experimental determination of the thermal conductivity of liquid UO2 near the melting point

M. Sheindlin, D. Staicu, C. Ronchi, L. Game-Arnaud, B. Remy, and A. Degiovanni

J. Appl. Phys. 101, 093508 (2007); http://dx.doi.org/10.1063/1.2721091 (9 pages) | Cited 4 times

Online Publication Date: 3 May 2007

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The article gives an account of measurements of the thermal conductivity of liquid UO2. The sample was heated up to above the melting point by a laser pulse of a controlled shape, and the produced thermogram of temperature history was measured by a fast and accurate pyrometer with a time resolution of 10 μs. The experiment shows that the rate of temperature increase during the ascending part of the pulse changes moderately across the melting point. Due to the high power input, this effect cannot be explained in terms of the sole intake of latent heat of fusion. By solving the related heat transfer equation with a 2D-axisymmetric numerical model, it is demonstrated that this feature depends principally on heat conduction in the sample, and proves that the thermal conductivities of solid and liquid are not very different. A theoretical sensitivity study assessing the influence of the liquid thermal conductivity on the pulse temperature evolution showed that the conductivity of the liquid can be deduced from the fitting of the thermograms with a numerical precision of the order of 1%. The analysis reveals that the thermal conductivity is weakly correlated with the effective heat losses during the pulse and to the melting enthalpy, so that the uncertainty in its evaluation by fitting the experimental thermograms with model predictions is satisfactory. The value of the thermal conductivity of liquid UO2 near the melting point resulted to be 2.6±0.35 W m−1 K−1, where the magnitude of the uncertainty is much lower than the scatter of the previously published, discordant measurements.
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66.25.+g Thermal conduction in nonmetallic liquids
64.70.D- Solid-liquid transitions
82.60.Cx Enthalpies of combustion, reaction, and formation

Co-doped anatase TiO2 nanofibers fabricated by electrospinning

C. W. Jia, E. Q. Xie, J. G. Zhao, and H. G. Duan

J. Appl. Phys. 101, 093509 (2007); http://dx.doi.org/10.1063/1.2724535 (4 pages) | Cited 6 times

Online Publication Date: 4 May 2007

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Co-doped TiO2 nanofibers with an average diameter of ∼ 70 nm were fabricated with electrospinning method. X-ray diffraction measurements show that the nanofibers possess pure anatase structure. The obtained nanofibers exhibit evident room temperature ferromagnetism through magnetic measurement. The photoluminescence of the Co-doped TiO2 nanofibers is composed of two emission bands attributed to self-trapped excitons and oxygen vacancies, different from that of pure TiO2 nanofibers which only includes emission due to self-trapped excitons. Photoluminescence intensity due to oxygen vacancies vary with annealing atmosphere and Co concentration, and the ferromagnetic moment increases with the increment of oxygen vacancies.
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61.46.-w Structure of nanoscale materials
75.50.Pp Magnetic semiconductors
75.75.-c Magnetic properties of nanostructures
75.50.Dd Nonmetallic ferromagnetic materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Hx Other solid inorganic materials

Compressional wave generation in droplets of water deposited on a quartz crystal: Experimental results and numerical calculations

G. Couturier, R. Boisgard, C. Jai, and J. P. Aimé

J. Appl. Phys. 101, 093510 (2007); http://dx.doi.org/10.1063/1.2730556 (5 pages) | Cited 2 times

Online Publication Date: 7 May 2007

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The generation of shear and compressional waves in liquids by AT-cut quartz crystals has received much attention in the past; however, this is not the case for droplets deposited onto quartz crystals. In this paper, we investigate the compressional wave generation in droplets and use different techniques to correlate the compressional wave generation to the shape of the droplets using frequency and dissipation measurements in an oscillator circuit while using a video camera to record the shape during evaporation. A good correlation between eigenmodes predicted by a finite element method and those obtained experimentally are observed.
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47.35.De Shear waves
47.55.dr Interactions with surfaces
47.80.Jk Flow visualization and imaging
47.11.Fg Finite element methods
64.70.F- Liquid-vapor transitions
02.70.Dh Finite-element and Galerkin methods

Determination of stacking fault probability in fcc Fe–Mn–Si–Al alloy by electron diffraction

X. D. Wang, B. X. Huang, Y. H. Rong, and L. Wang

J. Appl. Phys. 101, 093511 (2007); http://dx.doi.org/10.1063/1.2655682 (5 pages) | Cited 3 times

Online Publication Date: 8 May 2007

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The stacking disorder in the fcc structure of Fe–23Mn–2Si–2Al alloy after tensile testing at −75 °C was investigated by electron diffraction, using a relationship between the stacking fault probability and the shift of diffraction spots deduced in the present work (and based on Kakinoki’s theory [ Acta Crystallogr. 23, 875 (1967) ] and Kajiwara’s previous work [ Jpn. J. Appl. Phys. 9, 385 (1970); J. Phys. Soc. Jpn. 22, 795 (1967) ]). Shifts of diffraction spots along the [111] direction in the fcc structure were observed, and the stacking fault probabilities in two selected areas with different densities of stacking faults were determined as α = 0.15 and α = 0.35. The stacking fault probabilities measured by electron diffraction are much larger than average values determined by x-ray diffraction, indicating that the distribution of stacking faults is localized. A mechanism for the γfcc→εhcp transformation is suggested, whereby during deformation the following sequences take place: dissociation of perfect dislocation→localization of stacking faults→evolution from stacking disorder to stacking order→the formation of the perfect hcp martensite (α = 1) or the hcp martensite with stacking faults (α→1). This proposed mechanism for strain-induced hcp martensite formation should be also applicable to the thermally induced hcp martensite.
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61.72.Nn Stacking faults and other planar or extended defects
64.70.K- Solid-solid transitions

Effect of a Ta-Si-N diffusion barrier on the texture formation in thin Cu films

R. Hübner

J. Appl. Phys. 101, 093512 (2007); http://dx.doi.org/10.1063/1.2720100 (6 pages) | Cited 5 times

Online Publication Date: 9 May 2007

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Analyzing pole figures obtained by x-ray diffraction experiments, quantitative texture analyses are carried out on 50 nm thick Cu films sputter-deposited on oxidized Si substrates and on Ta-Si-N diffusion barrier films of various compositions. To explain the observed Cu texture formation during layer deposition, a model of two-dimensional grain growth in thin films is applied. In the case of silicon oxide substrates, a 〈111〉 Cu fiber texture component resulting from the minimization of the surface and interface energy is observed, in addition to a 〈100〉 component resulting from the minimization of the strain energy. For Cu films deposited onto Ta-Si-N diffusion barriers, preferred growth occurs only for 〈111〉-oriented Cu grains and their twins. The volume fractions of both components decrease with increasing N content of the diffusion barrier. Annealing of the Cu films at Tan = 600 °C results in a strengthening and a sharpening of the 〈111〉 component. Hence, both the chemical composition of the underlayer as well as a postdeposition anneal are observed to have a significant impact on the texture of thin Cu films.
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68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
68.55.A- Nucleation and growth
68.35.Fx Diffusion; interface formation
68.35.Md Surface thermodynamics, surface energies
81.40.Gh Other heat and thermomechanical treatments

Basic moments of phonon density of states spectra and characteristic phonon temperatures of group IV, III–V, and II–VI materials

Roland Pässler

J. Appl. Phys. 101, 093513 (2007); http://dx.doi.org/10.1063/1.2721749 (12 pages) | Cited 9 times

Online Publication Date: 9 May 2007

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We have redigitized a large variety of phonon density of states (PDOS) spectra, that have been published by diferent researchers for group IV (diamond, 3C-SiC, Si, and Ge), III–V (BN, BP, BAs, BSb, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, and InSb), and II–VI materials (ZnO, ZnS, ZnSe, ZnTe, CdS, and CdTe), including calculations of their moments, 〈εn〉, of orders n = −1, 1, 2, and 4. Notwithstanding the obvious differences in concrete shapes of spectra presented for one and the same material by different authors, the respective magnitudes of estimated moments have been found in most cases to be nearly the same (to within uncertainties of some few percent). For most materials under study, the average phonon temperatures of the lower and upper sections of PDOS spectra, ΘL and ΘU, are found to be by factors of order 0.6 lower or 1.4 higher, respectively, than the average phonon temperature, ΘP, of the total PDOS spectra. The estimated high-temperature limits of Debye temperatures, ΘD(∞), are found to be significantly higher (by factors of order 1.4) than ΘP, implying an order-of-magnitude equality, ΘD(∞) ≈ ΘU (within differences not exceeding an order of ±10%, for all materials under study). The phonon temperatures, Θg, that are effective in controlling the observable temperature dependences of fundamental energy gaps, Eg(T), are found to be usually of the same order as the respective average phonon temperatures, Θg ≈ ΘP. The existing differences between these two qualitatively different types of characteristic phonon temperatures are seen to be limited, for diamond, 3C-SiC, Si, Ge, AlN, GaN, GaP, GaAs, GaSb, InP, InSb, ZnS, ZnSe, ZnTe, and CdTe, to an order of ±12%. We design an exemplary way for precalculating harmonic parts of isochoric heat capacities on the basis of the estimated quadruplets of PDOS spectra moments. This novel calculation scheme is exemplified for silicon and germanium.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
65.40.Ba Heat capacity

High-resolution stress assessments of interconnect/dielectric electronic patterns using optically active point defects of silica glass as a stress sensor

Andrea Leto, Alessandro Alan Porporati, Wenliang Zhu, Martin Green, and Giuseppe Pezzotti

J. Appl. Phys. 101, 093514 (2007); http://dx.doi.org/10.1063/1.2723193 (14 pages) | Cited 12 times

Online Publication Date: 9 May 2007

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A piezospectroscopic (PS) cathodoluminescence (CL) study has been carried out on a Cu-Ta/SiOx (carbon-doped) model chip prepared on a Si substrate. The PS approach was applied to CL spectra arising from optically active point defects in dielectric silica. The red CL emission arising from nonbridging oxygen hole centers (NBOHC) in the carbon-doped SiOx dielectric layer was calibrated and used as a stress sensor. This approach enabled us to locate the trace of the residual stress tensor, as locally developed during manufacturing process in the dielectric interlayers between Cu-Ta interconnects. A minimally invasive electron beam allowed probing local residual stress fields with an improved spatial resolution as compared to more conventional photostimulated PS techniques applied to the Si substrate. In addition, a two-dimensional deconvolution procedure was attempted to retrieve the “true” residual stress distribution piled up between adjacent Cu-Ta lines, according to a theoretical model for embedded structural elements. As probed on the nanometer scale by the NBOHC sensor, the interfaces were found under a substantially enhanced residual stress, characteristic for low-temperature Si/SiOx growth in the presence of metallic interconnects. CL/PS spectroscopy represents an improved tool to quantitatively monitor the residual stresses developed at SiOx/metal interfaces, thus opening the possibility to systematically engineer the interface itself in search for high-reliability Si-based devices.
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07.10.-h Mechanical instruments and equipment
81.70.Fy Nondestructive testing: optical methods
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.J- Point defects and defect clusters
78.60.Hk Cathodoluminescence, ionoluminescence

Carrier relaxation dynamics and steady-state charge distributions in coupled InGaN/GaN multiple and single quantum wells

S. Khatsevich, D. H. Rich, S. Keller, and S. P. DenBaars

J. Appl. Phys. 101, 093515 (2007); http://dx.doi.org/10.1063/1.2727437 (9 pages) | Cited 1 time

Online Publication Date: 10 May 2007

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We have examined the carrier capture dynamics and excitation dependent charge distributions of coupled InGaN/GaN multiple quantum well samples. We measured the temporal evolution of time-delayed cathodoluminescence (CL) spectra to study the temperature- and excitation-dependent transfer of carriers from a surrounding confinement region into a coupled single quantum well. Samples possessing two different structures for the confinement region [i.e., number of quantum wells (QWs) and varying widths] were examined with CL. In order to study state filling of the SQW and QWs in the confinement region, we calculated the quasi-Fermi levels and carrier densities by utilizing a model that involves self-consistent solutions of the nonlinear Poisson-Schrödinger equation for wurtzite QWs including strain, deformation potentials, and polarization fields. Band-edge and effective mass parameters were first obtained from a strain- and In composition-dependent k⋅p calculation for wurtzite InxGa1−xN, using a 6×6 k⋅p Hamiltonian in the {0001} representation. The model shows that the difference in the quasi-Fermi levels between the confinement and SQW regions decreases with increasing excitation and temperature. Likewise, a reversal in the relative magnitude of the carrier densities between these two regions occurs at a certain temperature and excitation. Furthermore, the results for the model describing the steady-state excitation are consistent with those for the transient excitation in time-resolved CL, which also exhibit a marked increase in the rate of carrier transfer to the SQW region as the temperature increases.
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73.63.Hs Quantum wells
78.67.De Quantum wells
73.21.Fg Quantum wells
78.60.Hk Cathodoluminescence, ionoluminescence
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Low density of threading dislocations in AlN grown on sapphire

Nikolai Faleev, Hai Lu, and William J. Schaff

J. Appl. Phys. 101, 093516 (2007); http://dx.doi.org/10.1063/1.2728755 (5 pages) | Cited 7 times

Online Publication Date: 10 May 2007

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We report on high resolution x-ray diffraction studies of the crystalline perfection and the relaxation of elastic strain in AlN grown by MBE on sapphire(0001). Thin (200–300 nm thick) AlN layers were grown with a very low density of threading screw dislocations. A density of 1.75−8.5×105 cm−2, the lowest value ever reported for III-Nitride epitaxial layers, was observed in a surface layer formed over a defective nucleation layer. Residual elastic strain was found in investigated AlN layers. Stress was found to be close to that expected from thermal expansion mismatch between the AlN and sapphire(0001). A model for the structural transformation of crystalline defects accounts for these observations.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.D- Elasticity
65.40.De Thermal expansion; thermomechanical effects

Dislocation behavior in KCl crystal under uniaxial compression: Molecular dynamics simulation

Takahiro Kinoshita, Tsutomu Mashimo, and Katsuyuki Kawamura

J. Appl. Phys. 101, 093517 (2007); http://dx.doi.org/10.1063/1.2729459 (6 pages)

Online Publication Date: 10 May 2007

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Molecular dynamics simulations of dislocations behavior in KCl crystal under uniaxial compression along the [100], [110], and [111] axis directions were performed to discuss the elastoplastic transition under shock compression. The simulation results showed that the dislocation moved along about 45 deg to the uniaxial compression direction through the displacements of atomic lines around the dislocation core. Under uniaxial compression along the [111] axis direction, two extra half-(011) planes were inserted as dislocations in KCl crystal. The minimum stress for dislocation motion under the uniaxial compression along the [111] axis direction was much larger than those under the uniaxial compressions along the [100] and [110] axis directions. It was suggested that the large minimum stress for dislocation motion along the [111] axis direction was caused by the existence of two edge dislocations which were inserted as extra half-(011) planes. This anisotropic behavior was consistent with the experimental measurement of Hugoniot-elastic limit.
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61.72.Bb Theories and models of crystal defects
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
66.30.Lw Diffusion of other defects
62.50.-p High-pressure effects in solids and liquids

Atomistic analysis of the annealing behavior of amorphous regions in silicon

Pedro López, Lourdes Pelaz, Luis A. Marqués, and Iván Santos

J. Appl. Phys. 101, 093518 (2007); http://dx.doi.org/10.1063/1.2729468 (6 pages) | Cited 5 times

Online Publication Date: 10 May 2007

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We have analyzed the features of recrystallization of amorphous regions, using an atomistic amorphization-recrystallization model that considers the Si interstitial-vacancy pair as the building block for the amorphous phase. Both small amorphous pockets and large continuous amorphous layers are modeled as an accumulation of Si interstitial-vacancy pairs. In our model recrystallization is envisioned as a local rearrangement of atoms, the recrystallization rate of Si interstitial-vacancy pairs being determined by their local coordination. This feature explains the differences in the annealing behavior of amorphous regions with different topologies, the faster regrowth velocity of the damage tail compared with the continuous amorphous layer, and the independence of the regrowth velocity on the amorphous layer depth.
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81.05.Gc Amorphous semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Effects of ZnO buffer layers on the fabrication of GaN films using pulsed laser deposition

B. Y. Man, C. Yang, H. Z. Zhuang, M. Liu, X. Q. Wei, H. C. Zhu, and C. S. Xue

J. Appl. Phys. 101, 093519 (2007); http://dx.doi.org/10.1063/1.2730573 (5 pages) | Cited 3 times

Online Publication Date: 10 May 2007

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GaN thin films were deposited on Si (111) substrates using ZnO buffer layers by pulsed laser deposition of a GaN target in a nitrogen atmosphere. High-quality GaN thin films were obtained after annealing at 950 °C for 15 min in a NH3 atmosphere. The crystalline quality, composition, and surface morphology of the films were characterized by x-ray diffraction, Fourier transform infrared spectroscopy, and atomic force microscopy. Through analysis of the measured results, a conclusion was drawn that ZnO buffer layers and their crystalline quality affected the structural properties (crystalline quality, composition, and surface morphology) of GaN films. Crystalline ZnO buffer layers improved nucleation and growth of GaN films. Zn–O bonds are destroyed when the GaN films are annealed in ammonia (NH3) ambience; a few O and Zn atoms depart from their positions, while N and Ga atoms fill in the empty positions and form a hexagonal structure of a special component. The structure is propitious to the epitaxial growth of GaN, while the motion of atoms gives the grains of GaN more chances to move and form Ga–N bonds. The annealing time markedly affects the preparation of GaN films and the least annealing time is 15 min under our experimental conditions.
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81.05.Ea III-V semiconductors
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing

Equation of state of aluminum-iron oxide-epoxy composite

Jennifer L. Jordan, Louis Ferranti, Ryan A. Austin, Richard D. Dick, Jason R. Foley, Naresh N. Thadhani, David L. McDowell, and David J. Benson

J. Appl. Phys. 101, 093520 (2007); http://dx.doi.org/10.1063/1.2719272 (9 pages) | Cited 12 times

Online Publication Date: 11 May 2007

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We report on the measurements of the shock equation of state (Hugoniot) of an Al/Fe2O3/epoxy composite, prepared by epoxy cast curing of powder mixtures. Explosive loading, with Baratol, trinitrotoluene (TNT), and Octol, was used for performing experiments at higher pressures, in which case shock velocities were measured in the samples and aluminum, copper, or polymethyl methacrylate (PMMA) donor material, using piezoelectric pins. The explosive loading of the metal donors (aluminum and copper) will be discussed. Gas gun experiments provide complementary lower pressure data in which piezoelectric polyvinylidene fluoride (PVDF) stress gauges were used to measure the input and propagated stress wave profiles in the sample and the corresponding shock propagation velocity. The results of the Hugoniot equation of state are compared with mesoscale finite-element simulations, which show good agreement.
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64.30.-t Equations of state of specific substances
62.50.-p High-pressure effects in solids and liquids
62.65.+k Acoustical properties of solids

Stress anisotropy of the R-line luminescence lifetime in single crystal Cr-doped sapphire (ruby)

Samuel H. Margueron and David R. Clarke

J. Appl. Phys. 101, 093521 (2007); http://dx.doi.org/10.1063/1.2727443 (6 pages) | Cited 2 times

Online Publication Date: 11 May 2007

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The effect of uniaxial stress applied along the principal crystallographic directions (a, m, and c axes) of sapphire on the lifetime of the R-line luminescence doublet is described. All the measurements were performed at room temperature on samples cut from the same sapphire single crystal containing 250 ppm Cr3+ and the luminescence excited with a laser at 532 nm. The luminescence decays were all single exponentials with lifetimes that increased linearly with compression and decreased linearly in tension. The luminescence lifetimes in compression were crystallographically dependent with the variation in the basal plane being an order of magnitude greater than that along the c axis. The measured lifetimes were independent of the polarization of the luminescence emission. The stress anisotropy of the lifetimes is shown to be dominated by the σ emission and is consistent with estimates based on the anisotropy of coupling of 4T2 with the T1u distortion. The sum of the lifetime variation measured along the three principal crystallographic directions is equal to that reported for hydrostatic stresses. This is in agreement with calculations of the orientation dependence of the stress variation in dipole oscillator strength based on crystal field analysis.
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78.55.Hx Other solid inorganic materials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
71.70.Ch Crystal and ligand fields

Temperature-dependent structural and optical properties of SnS films

N. Koteeswara Reddy, Y. B. Hahn, M. Devika, H. R. Sumana, and K. R. Gunasekhar

J. Appl. Phys. 101, 093522 (2007); http://dx.doi.org/10.1063/1.2729450 (7 pages) | Cited 21 times

Online Publication Date: 11 May 2007

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The structural and optical properties of SnS films deposited on glass substrates have been studied at different temperatures under a vacuum of 10−6 Torr. At room temperature, the SnS films showed orthorhombic crystal structure with lattice parameters of a = 0.424, b = 1.107, and c = 0.3974 nm. These films also showed an optical band gap of ∼ 1.47 eV with a high absorption coefficient, ∼ 105 cm−1. X-ray diffraction studies at different temperatures (100−598 K) demonstrated that the structure of the SnS films remains constant. However, the volume of the unit cell of SnS films increased with the increase of temperature. It might be due to the expansion of the lattice. The effect of temperature (4−303 K) on the band gap of SnS films is also marginal ( ∼ 0.03 eV). It indicates that the SnS films are optically stable even at very low temperatures due to its stabilized structure. Therefore, SnS films offer an opportunity to be used as alternative semiconducting materials as active layers for the fabrication of optoelectronic devices.
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68.55.-a Thin film structure and morphology
78.66.Li Other semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.-a Optical materials
71.20.Nr Semiconductor compounds

Substitutional B in Si: Accurate lattice parameter determination

G. Bisognin, D. De Salvador, E. Napolitani, M. Berti, A. Carnera, S. Mirabella, L. Romano, M. G. Grimaldi, and F. Priolo

J. Appl. Phys. 101, 093523 (2007); http://dx.doi.org/10.1063/1.2720186 (8 pages) | Cited 4 times

Online Publication Date: 14 May 2007

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In this work the lattice deformation induced by substitutional B in Si is carefully determined by using different experimental techniques. The investigated Si1−xBx/Si layers x = (0.0012÷0.005) are grown by solid phase epitaxy of B-implanted preamorphized Si and by molecular beam epitaxy. Nuclear reaction analysis both in random and in channeling geometry, secondary ion mass spectrometry and high resolution x-ray diffraction allow to quantify the total amount of B and its lattice location, the B depth profile and the B-doped Si lattice parameter, respectively. The reasons for the large spread present in the data reported so far in literature are discussed. Our results, thanks to the synergy of the earlier techniques, lead to a significantly more accurate strain determination, that is in agreement with very recent ab initio theoretical calculations.
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61.66.Fn Inorganic compounds
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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)

The effect of thermal annealing on photoelectrochemical responses of WO3 thin films

Kwang-Soon Ahn, Se-Hee Lee, Anne C. Dillon, C. Edwin Tracy, and Roland Pitts

J. Appl. Phys. 101, 093524 (2007); http://dx.doi.org/10.1063/1.2729472 (4 pages) | Cited 16 times

Online Publication Date: 14 May 2007

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The photoelectrochemical responses of WO3 thin films have been investigated as a function of annealing temperature up to 600 °C. WO3 films were deposited on unheated substrates by thermal evaporation followed by annealing at temperatures of 300, 500, and 600 °C for 5 h in air. The WO3 film annealed at 500 °C shows the best photoelectrochemical response due to improved crystallinity and enhanced light absorption in the long-wavelength region. Although the WO3 film annealed at 600 °C exhibits better crystallinity and increased light absorption properties, it shows a decreased photoelectrochemical response in comparison to the one annealed at 500 °C. These results strongly suggests that the reduced amount of electrochemical reaction sites for the film annealed at 600 °C film plays a significant role in influencing the decreased photoresponse.
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82.45.Mp Thin layers, films, monolayers, membranes
82.45.Vp Semiconductor materials in electrochemistry
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.66.Li Other semiconductors
61.72.Cc Kinetics of defect formation and annealing

Asymmetric intermixing in a Co–Al thin film system: An investigation using coaxial impact collision ion scattering spectroscopy

H. M. Hwang, J. Y. Park, S. K. Jung, J. Lee, C. N. Whang, S.-P. Kim, S.-C. Lee, K.-R. Lee, and Y.-C. Chung

J. Appl. Phys. 101, 093525 (2007); http://dx.doi.org/10.1063/1.2730562 (6 pages) | Cited 2 times

Online Publication Date: 14 May 2007

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Surface structure evolution during atomic deposition in a Co–Al system was investigated using coaxial impact collision ion scattering spectroscopy (CAICISS). Half monolayer of Al and Co atoms were deposited on Co(0001) and Al(001) single crystal surfaces, respectively, in an ultrahigh-vacuum environment. CAICISS analysis of the deposited surface revealed an asymmetric interfacial reaction, as predicted by previous molecular dynamics simulations. Al atoms deposited on a Co substrate are placed on the surface with no interatomic intermixing. In contrast, significant surface intermixing with the deposited Co atoms occurs on the Al(001) substrate, resulting in the formation of a CoAl intermetallic surface layer of B2 structure. These asymmetric features would be important to the understanding of the structural evolution of thin film multilayers.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.Fx Diffusion; interface formation
68.47.De Metallic surfaces
66.30.Ny Chemical interdiffusion; diffusion barriers
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
68.43.Mn Adsorption kinetics
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