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15 Aug 2010

Volume 108, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 108, 041901 (2010); http://dx.doi.org/10.1063/1.3474648 (2 pages)

Sergei V. Kalinin, Nava Setter, and Andrei L. Kholkin
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back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Growth kinetics of AlN and GaN films grown by molecular beam epitaxy on R-plane sapphire substrates

R. Chandrasekaran, T. D. Moustakas, A. S. Ozcan, K. F. Ludwig, L. Zhou, and David J. Smith

J. Appl. Phys. 108, 043501 (2010); http://dx.doi.org/10.1063/1.3475521 (4 pages) | Cited 4 times

Online Publication Date: 16 August 2010

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This paper reports the growth by molecular beam epitaxy of AlN and GaN thin films on R-plane sapphire substrates. Contrary to previous findings that GaN grows with its (11math0) A-plane parallel to the (1math02) R-plane of sapphire, our results indicate that the crystallographic orientation of the III-nitride films is strongly dependent on the kinetic conditions of growth for the GaN or AlN buffer layers. Thus, group III-rich conditions for growth of either GaN or AlN buffers result in nitride films having (11math0) planes parallel to the sapphire surface, and basal-plane stacking faults parallel to the growth direction. The growth of these buffers under N-rich conditions instead leads to nitride films with (11math6) planes parallel to the sapphire surface, with inclined c-plane stacking faults that often terminate threading dislocations. Moreover, electron microscope observations indicate that slight miscut ( ∼ 0.5°) of the R-plane sapphire substrate almost completely suppresses the formation of twinning defects in the (11math6) GaN films.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
68.55.J- Morphology of films
61.66.Fn Inorganic compounds
61.72.Nn Stacking faults and other planar or extended defects

Amorphous copper tungsten oxide with tunable band gaps

Le Chen, Sudhakar Shet, Houwen Tang, Kwang-soon Ahn, Heli Wang, Yanfa Yan, John Turner, and Mowafak Al-Jassim

J. Appl. Phys. 108, 043502 (2010); http://dx.doi.org/10.1063/1.3475714 (5 pages) | Cited 3 times

Online Publication Date: 16 August 2010

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We report on the synthesis of amorphous copper tungsten oxide thin films with tunable band gaps. The thin films are synthesized by the magnetron cosputtering method. We find that due to the amorphous nature, the Cu-to-W ratio in the films can be varied without the limit of the solubility (or phase separation) under appropriate conditions. As a result, the band gap and conductivity type of the films can be tuned by controlling the film composition. Unfortunately, the amorphous copper tungsten oxides are not stable in aqueous solution and are not suitable for the application of photoelectrochemical splitting of water. Nonetheless, it provides an alternative approach to search for transition metal oxides with tunable band gaps.
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81.05.Gc Amorphous semiconductors
81.15.Cd Deposition by sputtering
73.61.Jc Amorphous semiconductors; glasses
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
68.55.ag Semiconductors

Nanoscale precipitation patterns in carbon–nickel nanocomposite thin films: Period and tilt control via ion energy and deposition angle

Gintautas Abrasonis, Thomas W. H. Oates, György J. Kovács, Jörg Grenzer, Per O. Å. Persson, Karl-Heinz H. Heinig, Andrius Martinavičius, Nicole Jeutter, Carsten Baehtz, Mark Tucker, Marcela M. M. Bilek, and Wolfhard Möller

J. Appl. Phys. 108, 043503 (2010); http://dx.doi.org/10.1063/1.3467521 (7 pages) | Cited 5 times

Online Publication Date: 16 August 2010

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Periodic precipitation patterns in C:Ni nanocomposites grown by energetic ion codeposition are investigated. Films were grown at room temperature by ionized physical vapor deposition using a pulsed filtered cathodic vacuum arc. We reveal the role of the film composition, ion energy and incidence angle on the film morphology using transmission electron microscopy and grazing incidence small angle x-ray scattering. Under these growth conditions, phase separation occurs in a thin surface layer which has a high atomic mobility due to energetic ion impacts. This layer is an advancing reaction front, which switches to an oscillatory mode, producing periodic precipitation patterns. Our results show that the ion induced atomic mobility is not random, as it would be in the case of thermal diffusion but conserves to a large extent the initial direction of the incoming ions. This results in a tilted pattern under oblique ion incidence. A dependence of the nanopattern periodicity and tilt on the growth parameters is established and pattern morphology control via ion velocity is demonstrated.
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68.55.aj Insulators
64.75.Jk Phase separation and segregation in nanoscale systems
64.75.St Phase separation and segregation in thin films
81.16.Rf Micro- and nanoscale pattern formation
78.70.Ck X-ray scattering
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Structural, electrical, and optical properties of atomic layer deposition Al-doped ZnO films

Parag Banerjee, Won-Jae Lee, Ki-Ryeol Bae, Sang Bok Lee, and Gary W. Rubloff

J. Appl. Phys. 108, 043504 (2010); http://dx.doi.org/10.1063/1.3466987 (7 pages) | Cited 43 times

Online Publication Date: 17 August 2010

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Al-doped ZnO (AZO) films of ∼ 100 nm thickness with various Al doping were prepared at 150 °C by atomic layer deposition on quartz substrates. At low Al doping, the films were strongly textured along the [100] direction, while at higher Al doping the films remained amorphous. Atomic force microscopy results showed that Al–O cycles when inserted in a ZnO film, corresponding to a few atomic percent Al, could remarkably reduce the surface roughness of the films. Hall measurements revealed a maximum mobility of 17.7 cm2/V s. Film resistivity reached a minima of 4.4×10−3 Ω cm whereas the carrier concentration reached a maxima of 1.7×1020 cm−3, at 3 at. % Al. The band gap of AZO films varied from 3.23 eV for undoped ZnO films to 3.73 eV for AZO films with 24.6 at. % Al. Optical transmittance over 80% was obtained in the visible region. The detrimental impact of increased Al resulting in decreased conductivity due to doping past 3.0 at. % is evident in the x-ray diffraction data, as an abrupt increase in the optical band gap and as a deviation from the Burstein–Moss effect.
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73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Ps Atomic force microscopy (AFM)
61.72.U- Doping and impurity implantation
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
72.80.Ey III-V and II-VI semiconductors

The influence of Pt redistribution on Ni1−xPtxSi growth properties

J. Demeulemeester, D. Smeets, C. M. Comrie, C. Van Bockstael, W. Knaepen, C. Detavernier, K. Temst, and A. Vantomme

J. Appl. Phys. 108, 043505 (2010); http://dx.doi.org/10.1063/1.3455873 (11 pages) | Cited 8 times

Online Publication Date: 18 August 2010

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We have studied the influence of Pt on the growth of Ni silicide thin films by examining the Pt redistribution during silicide growth. Three different initial Pt configurations were investigated, i.e., a Pt alloy (Ni+Pt/〈Si〉), a Pt capping layer (Pt/Ni/〈Si〉) and a Pt interlayer (Ni/Pt/〈Si〉), all containing 7 at. % Pt relative to the Ni content. The Pt redistribution was probed using in situ real-time Rutherford backscattering spectrometry (RBS) whereas the phase sequence was monitored during the solid phase reaction (SPR) using in situ real-time x-ray diffraction. We found that the capping layer and alloy exhibit a SPR comparable to the pure Ni/〈Si〉 system, whereas Pt added as an interlayer has a much more drastic influence on the Ni silicide phase sequence. Nevertheless, for all initial sample configurations, Pt redistributes in an erratic way. This phenomenon can be assigned to the low solubility of Pt in Ni2Si compared to NiSi and the high mobility of Pt in Ni2Si compared to pure Ni. Real-time RBS further revealed that the crucial issue determining the growth properties of each silicide phase is the Pt concentration at the Si interface during the initial stages of phase formation. The formation of areas rich in Pt reduce the Ni silicide growth kinetics which influences the phase sequence and properties of the silicides.
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68.55.aj Insulators
64.75.Bc Solubility
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Compositional dependent thin film stress states

B. Fu and G. B. Thompson

J. Appl. Phys. 108, 043506 (2010); http://dx.doi.org/10.1063/1.3462431 (6 pages) | Cited 3 times

Online Publication Date: 18 August 2010

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This paper addresses in situ stress evolution of two-component FexPt1−x, where x spanned 0 to 1, alloy thin films. The stresses of the high-temperature, quenched-in, solid solution phase was determined by in situ wafer curvature measurements during ambient temperature growth. The measured stresses were shown to be compositional dependent and spanned both compressive and tensile stress states. Under specific growth conditions, a “zero-stress” state could be achieved. The alloy stress states did not show any significant stress recovery upon ceasing the deposition, i.e. the stress state during growth was retained in the film. X-ray diffraction, transmission electron microscopy, and atom probe tomography were used to characterize the microstructures of each thin film. The evolution of the stress state with composition is described in terms of a chemical potential term for preferential segregation of one species in the alloy to the grain boundaries.
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68.60.Bs Mechanical and acoustical properties
62.20.F- Deformation and plasticity
65.40.G- Other thermodynamical quantities
81.40.Lm Deformation, plasticity, and creep
68.55.at Other materials
68.55.J- Morphology of films
81.30.Mh Solid-phase precipitation
61.72.Mm Grain and twin boundaries

Thermoreflectance of metal transducers for time-domain thermoreflectance

Yuxin Wang, Ji Yong Park, Yee Kan Koh, and David G. Cahill

J. Appl. Phys. 108, 043507 (2010); http://dx.doi.org/10.1063/1.3457151 (4 pages) | Cited 5 times

Online Publication Date: 18 August 2010

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We report measurements of the temperature dependence of the optical reflectivity, i.e., the thermoreflectance dR/dT, of 18 metallic elements at two laser wavelengths commonly used in ultrafast pump-probe experiments, 1.55 μm and 785 nm. The thermoreflectance is determined using time-domain thermoreflectance combined with measurements of the laser power and spot size and comparisons between the data and quantitative modeling of the temperature evolution at the surface of the sample. At a laser wavelength of 1.55 μm, four elements within this set of samples, Nb, Re, Ta, and V, have dR/dT comparable to or larger than 0.6×10−4 K−1. At a laser wavelength of 785 nm, the highest thermoreflectance is found in Al and Ta, dR/dT ≈ 2.1×10−4 K−1 and 2.2×10−4 K−1, respectively. Alloying Au with 5% Pd increases the optical absorption by a factor of 3 and the thermoreflectance by a factor of 2.
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78.20.N- Thermo-optic effects
07.07.Mp Transducers
42.25.Bs Wave propagation, transmission and absorption
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Influence of the excitonic broadening on the strong light-matter coupling in bulk zinc oxide microcavities

F. Médard, D. Lagarde, J. Zúñiga-Pérez, P. Disseix, M. Mihailovic, J. Leymarie, E. Frayssinet, J. C. Moreno, F. Semond, M. Leroux, and S. Bouchoule

J. Appl. Phys. 108, 043508 (2010); http://dx.doi.org/10.1063/1.3476553 (5 pages) | Cited 1 time

Online Publication Date: 18 August 2010

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We present an experimental study of the influence of excitonic broadening on the strong-coupling regime in a bulk-ZnO microcavity. At room temperature, the strong coupling is highlighted using both angle-resolved reflectivity and photoluminescence measurements; a Rabi splitting value of 40 meV is determined. The polaritonic behavior is also evidenced at low temperature, even if a bulklike reflectivity signature is observed in the excitonic range. Using transfer-matrix calculations, this phenomenon is explained through the influence of the huge excitonic absorption whose contribution depends on the broadening value. Finally, we demonstrate that this effect should not prevent a lasing from the polaritons.
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71.35.-y Excitons and related phenomena
78.55.Et II-VI semiconductors
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Optical properties of deformed few-layer graphenes with AB stacking

S. H. Lee, Y. H. Ho, C. W. Chiu, and M. F. Lin

J. Appl. Phys. 108, 043509 (2010); http://dx.doi.org/10.1063/1.3463390 (6 pages)

Online Publication Date: 18 August 2010

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Optical excitations of deformed AB-stacked graphenes are studied through the gradient approximation. The interlayer atomic interactions induce prominent peaks, shoulder structures, and transition gaps in the low-energy absorption spectra. The uniaxial stress changes the energy spacing at the band-edge states and the Fermi momenta, which reflects on the spectrum peak frequencies and the transition gaps, respectively. These optical characteristics are also influenced by the layer number. Besides, deformation shows some similar and different effects in comparison with electric and magnetic fields. These predicted optical properties can be verified by optical measurements.
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78.67.Wj Optical properties of graphene
81.05.ue Graphene
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Surface preparation and homoepitaxial deposition of AlN on (0001)-oriented AlN substrates by metalorganic chemical vapor deposition

A. Rice, R. Collazo, J. Tweedie, R. Dalmau, S. Mita, J. Xie, and Z. Sitar

J. Appl. Phys. 108, 043510 (2010); http://dx.doi.org/10.1063/1.3467522 (8 pages) | Cited 11 times

Online Publication Date: 19 August 2010

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Chemical surface treatments were conducted on mechanically polished (MP) and chemomechanically polished (CMP) (0001)-oriented single crystalline aluminum nitride (AlN) substrates to determine a surface preparation procedure for the homoepitaxial deposition of AlN epitaxial layers by metalorganic chemical vapor deposition. MP AlN substrates characterized by atomic force microscopy exhibited 0.5 nm rms roughness and polishing scratches, while CMP AlN substrates exhibited 0.1 nm rms roughness and were scratch-free. X-ray photoelectron spectroscopy analysis of MP and CMP AlN substrates indicated the presence of a surface hydroxide layer composed of mixed aluminum oxide hydroxide and aluminum trihydroxide. Wet etching with sulfuric and phosphoric acid mixtures reduced the amount of surface hydroxide. Ammonia annealing at 1250 °C converted the substrate hydroxide layer to AlN and increased the rms roughness of MP and CMP AlN substrates to 2.2 nm and 0.2 nm, respectively. AlN epitaxial layers were deposited at 1100–1250 °C under 20 Torr total pressure with a V/III ratio of 180–300 in either N2 or H2 diluent. High-resolution x-ray diffraction measurements revealed that AlN epitaxial layers deposited on MP substrates were strained due to nucleation and coalescence of AlN grains on the mechanically damaged surfaces. AlN deposited on CMP substrates was epitaxial and strain-free. Thermodynamic models for nitridation and AlN deposition were also proposed and evaluated.
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81.65.Ps Polishing, grinding, surface finishing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
68.35.bg Semiconductors
68.37.Ps Atomic force microscopy (AFM)

Equation of state of TiH2 up to 90 GPa: A synchrotron x-ray diffraction study and ab initio calculations

Patricia E. Kalita, Stanislav V. Sinogeikin, Kristina Lipinska-Kalita, Thomas Hartmann, Xuezhi Ke, Changfeng Chen, and Andrew Cornelius

J. Appl. Phys. 108, 043511 (2010); http://dx.doi.org/10.1063/1.3455858 (8 pages) | Cited 2 times

Online Publication Date: 20 August 2010

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We performed high-pressure studies and ab initio calculations of titanium hydride (TiH2), an important compound in hydrogen storage research. In situ, synchrotron x-ray diffraction studies were carried out in two separate compression runs: the first up to 19 GPa in quasihydrostatic conditions and the second up to 90 GPa in nonhydrostatic conditions, and followed by the subsequent decompression to ambient conditions. The pressure evolution of the diffraction patterns revealed a cubic [face-centered-cubic (fcc), Fm-3m] to tetragonal (body-centered-tetragonal (bct), I4/mmm) phase transition in TiH2 occurring at or below 0.6 GPa. The high-pressure tetragonal phase persisted up to 90 GPa. Upon decompression to ambient conditions the observed phase transition appeared irreversible. A third order Birch–Murnaghan fit of the unit cell volume as a function of pressure for all experimental points, yielded a zero pressure bulk modulus K0 = 142(7) GPa, and its pressure derivative K0′ = 3.3(0.2) for the high-pressure tetragonal phase of TiH2 and with K0′ held at four, K0 = 130(5) GPa. The experimental value of bulk modulus confirmed our ab initio calculations where K0 = 139.9 GPa, and K0′ = 3.7 for the high-pressure tetragonal phase of TiH2.
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64.30.Jk Equations of state of nonmetals
88.30.R- Hydrogen storage
62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli

A kinetics model for Tb3+ recombinations in low doped Tb:Lu1.8Y0.2SiO5 crystals

P. C. Ricci, M. Salis, R. Corpino, C. M. Carbonaro, E. Fortin, and A. Anedda

J. Appl. Phys. 108, 043512 (2010); http://dx.doi.org/10.1063/1.3467788 (6 pages) | Cited 2 times

Online Publication Date: 20 August 2010

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The detailed characterization of the terbium related optical properties of low doped oxyorthosilicates of lutetium and yttrium is reported. The introduction of terbium ions generates an ultraviolet absorption band peaked at about 242 nm and line shaped emissions in the 350–600 nm range. The transitions are related to the 5D3 and 5D4 levels and the analysis of the decay time measurements allows to individuate a cross relaxation mechanism among Terbium ions. We propose a three level kinetic model which is able to reproduce the experimental data allowing to discriminate among the radiative and nonradiative contributions to the transitions in the case of low content of Tb ions (nominal content 10 ppm). The reported study addresses two important goals, providing, from one side, a detailed characterization of possible inorganic phosphors, and from the other side, since traces of unwanted elements were identified in numerous commercial samples of cerium doped oxyorthosilicates, it can contribute to increase the performance of scintillator devices by revealing the optical features of one of the more diffuse and critical impurities.
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78.40.Ha Other nonmetallic inorganics
78.70.Ps Scintillation
71.20.Ps Other inorganic compounds
78.55.Hx Other solid inorganic materials

Electron irradiation effects on electrical and optical properties of sol-gel prepared ZnO films

J. S. Bhat, A. S. Patil, N. Swami, B. G. Mulimani, B. R. Gayathri, N. G. Deshpande, G. H. Kim, M. S. Seo, and Y. P. Lee

J. Appl. Phys. 108, 043513 (2010); http://dx.doi.org/10.1063/1.3452333 (8 pages) | Cited 4 times

Online Publication Date: 23 August 2010

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The effects of electron beam irradiation on the electrical and the optical properties of zinc oxide (ZnO) and aluminum-doped zinc oxide (ZnO:Al) thin films, prepared by the sol-gel technique, were investigated. The grain size, surface morphology, sheet resistance, optical constants, absorption edge, and direct and indirect optical band gaps of these films were analyzed before and after exposure to electron beam. The decrease in the structural homogeneity and the crystallinity of the films after exposure to electron irradiation is observed. The irradiation causes increase in the sheet resistance and blueshift in the absorption edge for both ZnO and ZnO:Al films. The change in carrier concentration due to doping as well as the exposure to electron beam are responsible for the modified electrical and optical properties.
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
73.61.Ga II-VI semiconductors
68.55.J- Morphology of films
61.82.Fk Semiconductors
61.80.Fe Electron and positron radiation effects

Photonic crystal composites-based wide-band optical collimator

Jinjie Shi, Bala Krishna Juluri, Sz-Chin Steven Lin, Mengqian Lu, Tieyu Gao, and Tony Jun Huang

J. Appl. Phys. 108, 043514 (2010); http://dx.doi.org/10.1063/1.3468242 (6 pages) | Cited 3 times

Online Publication Date: 23 August 2010

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Photonic crystal (PC) composites are sequenced series of PCs that feature the same periods but different filling fractions. By properly tuning the filling fractions of the individual PCs and merging the working band of each PC into a continuous frequency range, wide-band self-collimation of optical signals can be realized. The band diagrams and the equal-frequency contours of the PC structures were calculated through the plane wave expansion method and the finite-difference time-domain method was employed to simulate the propagation of electromagnetic waves through the PC structures. Our results show that while a single PC can only collimate optical waves over a narrow frequency range, a PC composite exhibits a much wider collimation band. Such a wide-band optical collimation lens can be useful in applications that demand directional optical energy flow over a long distance, such as optical imaging and biosensing.
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42.79.Ag Apertures, collimators
42.70.Qs Photonic bandgap materials
42.79.Bh Lenses, prisms and mirrors

Determination of thickness, refractive index, and spectral scattering of an inhomogeneous thin film with rough interfaces

J. Anto Pradeep and Pratima Agarwal

J. Appl. Phys. 108, 043515 (2010); http://dx.doi.org/10.1063/1.3478706 (9 pages) | Cited 1 time

Online Publication Date: 23 August 2010

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The magnitude of spectral transmittance and reflectance is affected by the presence of inhomogeneity and interfacial roughness. Therefore, the methods, based on the magnitude of spectral transmittance and reflectance, are not adequate for the determination of thickness and optical constants of films with inhomogeneity and interfacial roughness. The present article proposes a method for the determination of thickness and refractive index using only the positions of the interference fringes in spectral transmittance and reflectance at two different angles of incidence. The proposed method is verified through numerical simulations, which result in <1% error for the film thickness. The complete parametrical dependence of spectral transmittance and reflectance of inhomogeneous film with rough interfaces on a substrate have been worked out for the film on transparent and opaque substrates, respectively. The spectrum envelopes have been solved simultaneously and the mathematical formulae are given for the determination of spectral scattering due to inhomogeneity and interfacial roughness for both transmittance and reflectance cases.
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07.60.Hv Refractometers and reflectometers
68.55.jd Thickness
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Indium-doped ZnO nanowires: Optical properties and room-temperature ferromagnetism

K. W. Liu, M. Sakurai, and M. Aono

J. Appl. Phys. 108, 043516 (2010); http://dx.doi.org/10.1063/1.3464229 (5 pages) | Cited 11 times

Online Publication Date: 23 August 2010

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We report the optical and magnetic properties of ZnO, Zn0.97In0.03O, and Zn0.94In0.06O nanowires (NWs). All samples have similar wirelike shape with an average diameter of about 70 nm and a length of about 10 μm. The comparison of photoluminescence (PL) spectra at 10 K indicated that a new broad emission band appeared after indium doping, which is associated with donor-acceptor-pair recombination. Additionally, the intensity of oxygen-vacancies-induced visible emission increased with increasing In content, indicating that In doping can induce many oxygen vacancies. Furthermore, magnetic measurements revealed that pure ZnO NWs are diamagnetic, while indium-doped ZnO NWs exhibit intrinsic ferromagnetism at room temperature. With the increase in In content, the coercive field and the magnetic moment for indium-doped ZnO NWs increase largely. Ferromagnetic ordering can be interpreted as being due to O vacancies induced by In doping, which is in good agreement with PL results.
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81.07.Gf Nanowires
81.05.Dz II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
78.67.Uh Nanowires
75.50.Dd Nonmetallic ferromagnetic materials

Structure of the (0001) basal twin boundary in Bi2Te3

D. L. Medlin, Q. M. Ramasse, C. D. Spataru, and N. Y. C. Yang

J. Appl. Phys. 108, 043517 (2010); http://dx.doi.org/10.1063/1.3457902 (6 pages) | Cited 6 times

Online Publication Date: 24 August 2010

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We investigate the structure of the (0001) basal twin boundary in Bi2Te3. Electron diffraction measurements show that this interface corresponds to a 180° rotation of the crystal about the [0001] axis, an alignment that reverses the stacking of the basal planes. The basal planes in the perfect Bi2Te3 structure are arranged in a repeating sequence of five-layer wide Te(1)–Bi–Te(2)–Bi–Te(1) packets. Thus, it is possible for the twin interface to be located at one of three distinct locations: at the Te(2) layer, the Bi layer, or the Te(1) layer. Using aberration-corrected high-angle annular dark field scanning transmission electron microscopy, we show that the twin boundary is terminated at the Te(1) layer, where the stacking forms a double-layer of Te. Our observations are consistent with ab initio calculations, which predict this twin termination to have the lowest interfacial energy of the three configurations we considered. Our calculations and observations also find a small expansion in the interplanar spacing at the interface.
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61.72.Mm Grain and twin boundaries
61.66.Dk Alloys
68.35.Ct Interface structure and roughness
68.37.-d Microscopy of surfaces, interfaces, and thin films
65.40.gp Surface energy

Temperature-dependent photoconductivity in β-In2S3 single crystals

C. H. Ho, Y. P. Wang, C. H. Chan, Y. S. Huang, and C. H. Li

J. Appl. Phys. 108, 043518 (2010); http://dx.doi.org/10.1063/1.3478719 (4 pages) | Cited 7 times

Online Publication Date: 24 August 2010

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The solar-energy absorption material β-In2S3 was characterized using temperature-dependent photoconductivity (PC) measurements in the temperature range between 30 and 340 K in this study, and thermoreflectance (TR) and photoluminescence (PL) measurements were carried out to identify near-band-edge transitions in the β-In2S3 tetragonal crystal. The experimental analyses of PL, PC, and TR confirmed that β-In2S3 is a direct semiconductor with a band gap of 2.073 eV at 30 K and 1.935 eV at 300 K. The PL and PC spectra manifest some defect-related features in the β-In2S3 single crystal. Two defect emissions and two band-edge luminescences were simultaneously detected in the PL spectrum at 30 K, and the temperature-dependent PC spectra of β-In2S3 from 160 to 300 K reveal an additional defectlike or band-to-band feature with an energy located above the conduction band edge (EC). The temperature dependences of the PC transition features in the β-In2S3 defect crystal were analyzed. The origin and mechanism of all defect states and band-edge transitions in the β-In2S3 single crystal are evaluated and discussed.
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81.05.Hd Other semiconductors
72.40.+w Photoconduction and photovoltaic effects
78.56.-a Photoconduction and photovoltaic effects
78.20.N- Thermo-optic effects
78.55.Hx Other solid inorganic materials
71.55.Ht Other nonmetals

Light-induced point defect reactions of residual iron in crystalline silicon after aluminum gettering

D. Abdelbarey, V. Kveder, W. Schröter, and M. Seibt

J. Appl. Phys. 108, 043519 (2010); http://dx.doi.org/10.1063/1.3474658 (6 pages) | Cited 3 times

Online Publication Date: 25 August 2010

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Deep level transient spectroscopy is used to study light-induced reactions of residual iron impurities after aluminum gettering (AlG) in crystalline silicon. White-light illumination at room temperature leads to the formation of a defect which is associated with a donor level at 0.33 eV above the valence band. This defect is stable up to about 175 °C where it dissociates reversibly in case of small iron concentrations and irreversibly for high iron concentrations. Since marker experiments using gold and platinum diffusion show a high vacancy concentration after AlG a tentative identification of the new defect as the metastable iron-vacancy pair is proposed.
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71.55.Cn Elemental semiconductors
75.30.Hx Magnetic impurity interactions
61.72.jd Vacancies
82.30.-b Specific chemical reactions; reaction mechanisms
61.80.-x Physical radiation effects, radiation damage
61.82.Fk Semiconductors

Spectroscopic and upconversion properties of erbium-doped potassium lithium tantalate niobate crystals under 800 nm femtosecond laser excitation

Lei Li, Zhongxiang Zhou, Hao Tian, Dewei Gong, Zhenling Yang, and Yanqiang Yang

J. Appl. Phys. 108, 043520 (2010); http://dx.doi.org/10.1063/1.3475511 (7 pages) | Cited 5 times

Online Publication Date: 25 August 2010

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The single crystals of tungsten bronze-type potassium lithium tantalate niobate doped with three concentrations erbium with good quality are grown using top-seed solution growth method. The unpolarized ultraviolet-visible-near infrared optical absorption spectra of these single crystals are measured at room temperature. The green and red upconversion emission properties are analyzed with respect to steady-state spectra and decay behaviors under 800 nm femtosecond laser excitation. The spectroscopic properties of Er3+ ions are studied on the basis of the Judd–Ofelt theory. 12 Er3+ ions absorption bands are observed ranging from 350 to 1650 nm, the lower limit is also the ultraviolet absorption edge of these crystals. The fluorescence branching ratio and radiative lifetime are calculated to support the upconversion mechanism. The relationship of the Judd–Ofelt parameters Ω4<Ω6 of Er3+ in these crystals is different from the general trend Ω2>Ω4>Ω6. Experimental results indicate that upconversion emission is a two-photon process. It follows that the shortening of lifetime and the increasing of intensities of red emission are due to the increase in Er3+ ions cluster sites. Excited state absorption and energy transfer processes lead to the green emission while cross relaxation process produces the red emission.
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78.55.Hx Other solid inorganic materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
61.72.up Other materials
81.10.Dn Growth from solutions

X-ray diffuse scattering from threading dislocations in epitaxial GaN layers

M. Barchuk, V. Holý, B. Miljević, B. Krause, T. Baumbach, J. Hertkorn, and F. Scholz

J. Appl. Phys. 108, 043521 (2010); http://dx.doi.org/10.1063/1.3460803 (7 pages) | Cited 2 times

Online Publication Date: 25 August 2010

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In this article, we combine diffuse x-ray scattering with a Monte Carlo simulation method for the determination of the dislocation density in thin heteroepitaxial layers. As a model, we consider GaN epitaxial layers containing threading dislocations perpendicular to the surface. The densities of particular types of threading dislocations following from the comparison of measured and simulated distributions of diffusely scattered x-ray intensity are compared with the dislocation densities determined by etching. A good agreement was found.
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81.05.Ea III-V semiconductors
68.55.ag Semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.70.Ck X-ray scattering
61.43.Bn Structural modeling: serial-addition models, computer simulation

2.0 μm emission properties and energy transfer processes of Yb3+/Ho3+ codoped germanate glass

Rongrong Xu (徐茸茸), Jiajia Pan (潘佳佳), Lili Hu (胡丽丽), and Junjie Zhang (张军杰)

J. Appl. Phys. 108, 043522 (2010); http://dx.doi.org/10.1063/1.3468726 (7 pages) | Cited 10 times

Online Publication Date: 25 August 2010

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Ho3+ doped germanate glass sensitized by Yb3+ has been investigated for potential application as a near-infrared laser material. The characteristic temperatures are determined by differential scanning calorimeter, and the absorption and emission spectra are measured. According to absorption spectra, Judd–Ofelt parameters and radiative transition probabilities are calculated and analyzed by Judd–Ofelt theory. The intensity of emission spectra shows a strong dependence upon the Yb3+ concentration. The result also indicates that Yb3+ plays an important role in the emission of 2.0 μm by transferring the 980 nm excitation energy to Ho3+. The energy transfer process from Yb3+ to Ho3+ is analyzed and the result shows that coefficient of the forward energy transfer Yb3+→Ho3+ is 19 times of magnitude larger than that of the backward energy transfer Yb3+←Ho3+. It is found that the highest gain in 2.0 μm region could be achieved from the germanate glass with 5.0 mol % Yb2O3 and 1.0 mol % Ho2O3. The present Yb3+/Ho3+ codoped germanate glass with high emission cross section of Ho3+:5I7→5I8 at 2.0 μm and efficient energy transfer from Yb3+ to Ho3+ will be a suitable material for developing solid state lasers around 2.0 μm.
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42.70.Ce Glasses, quartz
78.40.Pg Disordered solids
78.55.Hx Other solid inorganic materials
78.30.Hv Other nonmetallic inorganics
71.55.Ht Other nonmetals

Modeling the effect of native and laser-induced states on the dielectric breakdown of wide band gap optical materials by multiple subpicosecond laser pulses

Luke A. Emmert, Mark Mero, and Wolfgang Rudolph

J. Appl. Phys. 108, 043523 (2010); http://dx.doi.org/10.1063/1.3457791 (7 pages) | Cited 12 times

Online Publication Date: 26 August 2010

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A model for the multiple-pulse laser-induced breakdown behavior of dielectrics is presented. It is based on a critical conduction band (CB) electron density leading to dielectric breakdown. The evolution of the CB electron density during the pulse train is calculated using rate equations involving transitions between band and mid-gap states (native and laser-induced). Using realistic estimations for the trap density and ionization cross-section, the model is able to reproduce the experimentally observed drop in the multiple-pulse damage threshold relative to the single-pulse value, as long as the CB electron density is controlled primarily by avalanche ionization seeded by multiphoton ionization of the traps and the valence band. The model shows that at long pulse duration, the breakdown threshold becomes more sensitive to presence of traps close (within one photon energy) to the CB. The effect of native and laser-induced defects can be distinguished by their saturation behavior. Finally, measurements of the multiple-pulse damage threshold of hafnium oxide films are used to illustrate the application of the model.
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77.22.Jp Dielectric breakdown and space-charge effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
42.79.Wc Optical coatings
42.70.-a Optical materials
77.55.-g Dielectric thin films

Strong light-matter coupling in bulk GaN-microcavities with double dielectric mirrors fabricated by two different methods

F. Réveret, K. Bejtka, P. R. Edwards, S. Chenot, I. R. Sellers, P. Disseix, A. Vasson, J. Leymarie, J. Y. Duboz, M. Leroux, F. Semond, and R. W. Martin

J. Appl. Phys. 108, 043524 (2010); http://dx.doi.org/10.1063/1.3477450 (6 pages) | Cited 3 times

Online Publication Date: 26 August 2010

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Two routes for the fabrication of bulk GaN microcavities embedded between two dielectric mirrors are described, and the optical properties of the microcavities thus obtained are compared. In both cases, the GaN active layer is grown by molecular beam epitaxy on (111) Si, allowing use of selective etching to remove the substrate. In the first case, a three period Al0.2Ga0.8N/AlN Bragg mirror followed by a λ/2 GaN cavity are grown directly on the Si. In the second case, a crack-free 2 μm thick GaN layer is grown, and progressively thinned to a final thickness of λ. Both devices work in the strong coupling regime at low temperature, as evidenced by angle-dependent reflectivity or transmission experiments. However, strong light-matter coupling in emission at room temperature is observed only for the second one. This is related to the poor optoelectronic quality of the active layer of the first device, due to its growth only 250 nm above the Si substrate and its related high defect density. The reflectivity spectra of the microcavities are well accounted for by using transfer matrix calculations.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors

Strong strain-dependent elastic stiffness in ultrathin Pt films on MgO

N. Nakamura, Y. Kake, H. Ogi, and M. Hirao

J. Appl. Phys. 108, 043525 (2010); http://dx.doi.org/10.1063/1.3460799 (4 pages) | Cited 1 time

Online Publication Date: 27 August 2010

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In this study, strong strain dependence of the elastic stiffness is found in polycrystalline Pt films. Epitaxial and polycrystalline Pt films thinner than 100 nm were deposited on monocrystal MgO substrates and resonance frequency of longitudinal standing wave in the film thickness direction was measured by picosecond ultrasound. In epitaxial Pt film, the resonance frequency was comparable to or smaller than the value expected from the elastic stiffness of bulk Pt, indicating softening of epitaxial Pt films, where nanoscale defects were observed: the softening was attributed to the defects. However, in polycrystalline Pt films, resonance frequency increased as the film thickness decreased and when the film thickness was smaller than 20 nm, the value exceeded the predicted value from the bulk stiffness, indicating the stiffening of the Pt film. Furthermore, resonance frequency showed good correlation with the strain. This trend is expected considering the higher elasticity. However, the slope between the resonance frequency and the strain is ten times as large as the value deduced from third-order elastic constant.
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68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dq Other elastic constants
62.65.+k Acoustical properties of solids
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