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1 Feb 2008

Volume 103, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 103, 031101 (2008); http://dx.doi.org/10.1063/1.2836410 (35 pages)

Ce-Wen Nan, M. I. Bichurin, Shuxiang Dong, D. Viehland, and G. Srinivasan
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Formation of a low energy grain boundary in ZnO: The structural unit concept in hexagonal symmetry materials

P. Ruterana, M. Abouzaid, A. Béré, and J. Chen

J. Appl. Phys. 103, 033501 (2008); http://dx.doi.org/10.1063/1.2837027 (7 pages) | Cited 6 times

Online Publication Date: 1 February 2008

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ZnO thin films prepared by magnetron sputtering on c-plane sapphire may exhibit a columnar growth with an average column diameter depending on the deposition temperature. In this case two epitaxial relationships coexist and adjacent columns are rotated, one from the other, by 90° around the [0001] direction. The long range rotation between domains is in agreement with the theoretical epitaxial relationships, but the local angles oscillate between 27° and 32° due to the formation of interfaces, which settle into low energy configurations with grain boundary dislocations of a Burgers vectors and 5/7 aligned structural units for the 32.2° tilt angle.
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61.72.Mm Grain and twin boundaries
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.)
68.37.Lp Transmission electron microscopy (TEM)

Electroacoustic simulation and experiment on a miniature loudspeaker for cellular phones

Jin H. Huang, Hong-Ching Her, Y. C. Shiah, and Shaw-Jyh Shin

J. Appl. Phys. 103, 033502 (2008); http://dx.doi.org/10.1063/1.2837112 (7 pages) | Cited 2 times

Online Publication Date: 1 February 2008

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The performance of a miniature loudspeaker used in computer, communication, and consumer electronics products is an integrated function with coupled magnetic, electrical, mechanical, and acoustical fields. Through the finite element method, optimal design parameters to enhance the performance of a miniature loudspeaker are obtained. The sound pressure response of the miniature loudspeaker is simulated by using an equivalent circuit method. Its electrical driver, mechanical motion, and acoustical radiation are analogized by their equivalent elements individually. For the present work, such an analysis is carried out for a miniature loudspeaker manufactured in the cellular phone industry. All speaker parameters in the analysis are experimentally measured. Sound pressure responses are experimentally taken by PULSE Electroacoustics in an anechoic chamber. The equivalent-circuit analysis show fairly good agreement with the experimental results.
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02.70.Dh Finite-element and Galerkin methods
43.38.Ja Loudspeakers and horns, practical sound sources
43.58.-e Acoustical measurements and instrumentation

Cross-sectional transmission electron microscopy observations of structural damage in Al0.16Ga0.84N thin film under contact loading

Sheng-Rui Jian, Jenh-Yih Juang, and Yi-Shao Lai

J. Appl. Phys. 103, 033503 (2008); http://dx.doi.org/10.1063/1.2836939 (5 pages) | Cited 13 times

Online Publication Date: 4 February 2008

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This article reports a nanomechanical response study of the contact-induced deformation behavior in Al0.16Ga0.84N thin film by means of a combination of nanoindentation and the cross-sectional transmission electron microscopy (XTEM) techniques. Al0.16Ga0.84N thin film is deposited by using the metal-organic chemical vapor deposition method. Hardness and Young’s modulus of the Al0.16Ga0.84N films were measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements mode. The obtained values of the hardness and Young’s modulus are 19.76±0.15 and 310.63±9.41 GPa, respectively. The XTEM images taken in the vicinity just underneath the indenter tip revealed that the multiple “pop-ins” observed in the load-displacement curve during loading are due primarily to the activities of dislocation nucleation and propagation. The absence of discontinuities in the unloading segments of the load-displacement curve suggests that no pressure-induced phase transition was involved.
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62.20.-x Mechanical properties of solids
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Standing-wave effects in grazing-incidence x-ray diffraction from polycrystalline multilayers

J. Krčmář, V. Holý, L. Horák, T. H. Metzger, and J. Sobota

J. Appl. Phys. 103, 033504 (2008); http://dx.doi.org/10.1063/1.2836974 (7 pages) | Cited 1 time

Online Publication Date: 4 February 2008

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The intensity of x-ray diffraction from a polycrystalline multilayer in a grazing-incidence scattering geometry is modulated by a standing wave created by the interference of the radiation transmitted through the multilayer stack with the wave field specularly reflected from the superlattice interfaces. Similarly, the radiation being diffracted from the polycrystalline structure is reflected specularly from the interfaces and a standing-wave interference pattern results as well. This effect is demonstrated by a series of diffraction measurements on C/Ni periodic multilayers; the experimental data have been modeled using the distorted-wave Born approximation and a very good correspondence with the experiments was achieved. The method was used for the study of the profiles of the crystallite sizes and strains in multilayers.
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68.65.Ac Multilayers
68.65.Cd Superlattices
68.49.Uv X-ray standing waves
68.35.Ct Interface structure and roughness
62.65.+k Acoustical properties of solids
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Atomic level mixing induced by Kr irradiation of FeCo/Cu multilayers

I. L. Graff, J. Geshev, S. R. Teixeira, L. Amaral, and A. Traverse

J. Appl. Phys. 103, 033505 (2008); http://dx.doi.org/10.1063/1.2836975 (11 pages) | Cited 1 time

Online Publication Date: 5 February 2008

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The effects of Kr ion irradiation of FexCo1−x/Cu multilayers are investigated by means of magnetic and x-ray measurements. The irradiation was performed at room temperature with 600 keV of Kr, and the fluences were ranged from 1×1015 to 5×1015 ions/cm2. X-ray diffraction patterns show that the irradiation was able to produce a significant grain growth and, at the same time, it triggered a strain release. The x-ray absorption measurements around Fe K edge have shown that the FeCo environment changed from bcc, for the as-deposited multilayer, to fcc after appropriate fluence, depending on the Cu thickness and on the Fe/Co content. For 50 Å of Cu, the phase transformation occurs even for the lowest fluence, regardless the Fe/Co concentration. For 25 Å of Cu, it depends on the Fe/Co concentration. After irradiation, the saturation magnetization suffers a strong decrease, especially for 50 Å of Cu. The temperature for the onset of irreversibility also decreases with irradiation, again being the effect stronger for 50 Å of Cu. These data indicate that Kr irradiation induced mixing between Cu and FeCo, even though Cu is immiscible with Fe and Co in the equilibrium state.
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68.65.Ac Multilayers
61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
64.70.kd Metals and alloys

X-ray diffraction, μ-Raman spectroscopic studies on CeO2−RE2O3 (RE = Ho, Er) systems: Observation of parasitic phases

B. P. Mandal, M. Roy, V. Grover, and A. K. Tyagi

J. Appl. Phys. 103, 033506 (2008); http://dx.doi.org/10.1063/1.2837042 (7 pages) | Cited 14 times

Online Publication Date: 5 February 2008

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The phase relations in CeO2−Ho2O3 and CeO2−Er2O3 systems have been established under the slow-cooled conditions. As per x-ray diffraction (XRD), in both the series a single-phasic solid solution forms up to the nominal composition Ce0.6RE0.4O1.8 (RE = Ho, Er) retaining the F-type structure of parent ceria. In Ce1−xErxO2−x/2 system the presence of microdomains of C-type phase have been revealed by Raman spectroscopy for composition x = 0.4, which has been identified as single phasic by XRD. Photoluminescence studies also show that biphasic region commences from x = 0.4 for Ce1−xHoxO2−x/2 series. The biphasicity continues until x = 0.7 for both the series. From x = 0.8 the solid solutions exist as C-type single phasic, which is isotypic to another end member RE2O3 (RE = Ho, Er) and as revealed by both XRD and Raman spectroscopy. High temperature XRD studies show that no temperature induced phase change has been observed in either of the series until 1273 K. In this work photoluminescence data was used to delineate the phase boundary.
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64.75.Nx Phase separation and segregation in solid solutions
81.30.Dz Phase diagrams of other materials
78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials

Magnetic characterization of magnetic tunnel junction devices using circle transfer curves

N. S. Safron, B. D. Schrag, Xiaoyong Liu, Weifeng Shen, D. Mazumdar, M. J. Carter, and Gang Xiao

J. Appl. Phys. 103, 033507 (2008); http://dx.doi.org/10.1063/1.2837115 (8 pages) | Cited 1 time

Online Publication Date: 5 February 2008

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We describe new characterization methods that allow an accurate determination of all of the magnetic parameters that govern the behavior of magnetoresistive devices. These characterization methods are explained and used to measure the magnetic properties of MgO-based magnetic tunnel junction (MTJ) devices with magnetoresistance values of over 150%. We will show that the analysis of so-called “circle transfer curves,” which are measurements of the device magnetoresistance in a rotating, constant-magnitude applied field, can accurately determine the magnitude and direction of the free layer anisotropy as well as the pinned layer orientation and exchange bias strength. We also show how a measurement of the MTJ’s remnant resistance curve, obtained by saturating the MTJ at different field angles and then removing the applied field, can provide additional information on the free layer anisotropy characteristics. We will also compare our results with values extracted from traditional Stoner-Wohlfarth asteroid curves. Finally, we show that the extracted parameters can accurately predict the shape of traditional MTJ transfer curves.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.30.Gw Magnetic anisotropy

Intrinsic and extrinsic diffusion of phosphorus, arsenic, and antimony in germanium

Sergej Brotzmann and Hartmut Bracht

J. Appl. Phys. 103, 033508 (2008); http://dx.doi.org/10.1063/1.2837103 (7 pages) | Cited 46 times

Online Publication Date: 6 February 2008

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Diffusion experiments of phosphorus (P), arsenic (As), and antimony (Sb) in high purity germanium (Ge) were performed at temperatures between 600 and 920 °C. Secondary ion mass spectrometry and spreading resistance profiling were applied to determine the concentration profiles of the chemically and electrically active dopants. Intrinsic and extrinsic doping conditions result in a complementary error function and box-shaped diffusion profiles, respectively. These profiles demonstrate enhanced dopant diffusion under extrinsic doping. Accurate modeling of dopant diffusion is achieved on the basis of the vacancy mechanism taking into account singly negatively charged dopant-vacancy pairs and doubly negatively charged vacancies. The activation enthalpy and pre-exponential factor for dopant diffusion under intrinsic condition were determined to 2.85 eV and 9.1 cm2 s−1 for P, 2.71 eV and 32 cm2 s−1 for As, and 2.55 eV and 16.7 cm2 s−1 for Sb. With increasing atomic size of the dopants the activation enthalpy decreases. This is attributed to differences in the binding energy of the dopant-vacancy pairs.
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66.30.Lw Diffusion of other defects
61.72.jd Vacancies
61.72.uf Ge and Si
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Photothermal thickness measurement of multilayered structures: An experimental and numerical analysis

P. Suter and T. Graf

J. Appl. Phys. 103, 033509 (2008); http://dx.doi.org/10.1063/1.2837830 (9 pages) | Cited 2 times

Online Publication Date: 6 February 2008

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The evolution of the surface temperature of flash-illuminated layered structures was studied by means of photothermal radiometry, the finite element method, and the Green’s formalism. The potential of a simple tabletop experiment to extract the sequence and thickness of the layers was investigated. Keeping the complexity low, only one parameter can be determined independently, for instance the absolute value and small variations of the top layer thickness. Our method is straightforward, accurate, and well-suited for online thickness detection.
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07.20.-n Thermal instruments and apparatus
07.60.Dq Photometers, radiometers, and colorimeters
02.70.Dh Finite-element and Galerkin methods

Structural and optical properties of epitaxial CaxBa1−xNb2O6 thin films grown on MgO by pulsed laser deposition

Paul F. Ndione, Mounir Gaidi, Christophe Durand, Mohamed Chaker, Roberto Morandotti, and Grégory Rioux

J. Appl. Phys. 103, 033510 (2008); http://dx.doi.org/10.1063/1.2838176 (5 pages) | Cited 6 times

Online Publication Date: 6 February 2008

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In the present work, we investigate in detail the effect of both the deposition temperature and the cooling rate on the growth of calcium barium niobate (CBN) thin films on a magnesium oxide (MgO) single crystal substrate. As revealed by x-ray diffraction measurements, epitaxy occurs for films deposited at 800 °C with a slow in situ cooling rate. We have also investigated the chemical composition of the films by way of a Rutherford backscattering spectroscopy technique and of an elastic recoil detection analysis, which reveal a good stoichiometry for our samples. In addition, optical analysis (UV-visible spectroscopy and spectroscopic ellipsometry) is performed on both polycrystalline and epitaxial films. A high transmittance (>85%) and a refractive index close to that observed for bulk crystal are obtained for epitaxial CBN films deposited at a low oxygen pressure. X-ray reflectivity measurements have enabled us to correlate the density of the films with their refractive indices.
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68.55.A- Nucleation and growth
68.60.-p Physical properties of thin films, nonelectronic
78.66.-w Optical properties of specific thin films
81.15.Fg Pulsed laser ablation deposition

The microstructure and electrical transport properties of immiscible copper-niobium alloy thin films

Rajarshi Banerjee, Sangita Bose, Arda Genc, and Pushan Ayyub

J. Appl. Phys. 103, 033511 (2008); http://dx.doi.org/10.1063/1.2836970 (7 pages) | Cited 2 times

Online Publication Date: 7 February 2008

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Mutually immiscible in the solid state, copper and niobium exhibit a relatively strong clustering (phase separating) tendency in the liquid state and can therefore only be alloyed in a highly metastable form: for example, by vapor quenching. We have deposited metastable Cu–Nb alloy thin films with nominal compositions ranging from 5 to 90 at. % Nb by magnetron cosputtering. The microstructure of these films depends strongly on the composition and ranges from coarse-grained solid solutions for Cu-rich and Nb-rich compositions to phase-separated amorphous mixtures when the two elements are in comparable amounts. The crystalline Cu- or Nb-rich compositions exhibit positive temperature coefficients of resistivity (TCR) with the Cu–90 at. % Nb film exhibiting a superconducting transition with (TC)onset ∼ 4.5 K. The amorphous films show high room temperature resistivity, a negative TCR, and composition dependent superconducting transitions. We investigate the relation between the microstructure, phase stability, and the electrical transport properties.
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73.61.At Metal and metallic alloys
64.75.-g Phase equilibria
81.15.Cd Deposition by sputtering
74.62.-c Transition temperature variations, phase diagrams
61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.-a Thin film structure and morphology

Transition behavior of surface morphology evolution of Si(100) during low-energy normal-incidence Ar+ ion bombardment

Gozde Ozaydin, Karl F. Ludwig, Jr., Hua Zhou, Lan Zhou, and Randall L. Headrick

J. Appl. Phys. 103, 033512 (2008); http://dx.doi.org/10.1063/1.2837101 (5 pages) | Cited 7 times

Online Publication Date: 7 February 2008

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The temperature dependence of the surface morphology evolution during 1000 eV Ar+ ion bombardment of Si(100) surfaces at normal incidence is studied in real time. At room temperature the surface is amorphized by the ion bombardment but remains smooth. Calculations suggest this may be due to ion impact induced lateral mass redistribution. However, at the fluxes used here, surface roughening occurs above 400 °C, and in the range of 400 °C to 500 °C a transition region from amorphous to crystalline surface is observed. Above 500 °C, the surface remains crystalline and the growing corrugations exhibit dynamic scaling with power law growth in amplitude and characteristic length scale. This behavior is characteristic of instabilities driven by surface diffusion processes.
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68.47.Fg Semiconductor surfaces
68.35.Rh Phase transitions and critical phenomena
68.35.bg Semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.Fx Diffusion; interface formation

Thermal properties of cubic KTa1−xNbxO3 crystals

X. P. Wang, J. Y. Wang, H. J. Zhang, Y. G. Yu, J. Wu, W. L. Gao, and R. I. Boughton

J. Appl. Phys. 103, 033513 (2008); http://dx.doi.org/10.1063/1.2838221 (6 pages) | Cited 5 times

Online Publication Date: 7 February 2008

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Cubic potassium tantalite niobate [KTa1−xNbxO3 (KTN)] crystals of large size, good quality, and varying Nb concentration have been grown by the Czochralski method and their thermal properties have been systematically studied. The melting point, molar enthalpy of fusion, and molar entropy of fusion of the crystals were determined to be: 1536.9 K, 12 068.521 J mol−1, and 7.85 J K−1 mol−1 for KTa0.67Nb0.33O3; and 1520.61 K, 15 352.511 J mol−1, and 10.098 J K−1 mol−1 for KTa0.67Nb0.33O3, respectively. Based on the data, the Jackson factor was calculated to be 0.994f and 1.214f for KTa0.67Nb0.33O3 and KTa0.63Nb0.37O3, respectively. The thermal expansion coefficients over the temperature range of 298.15−773.15 K are: α = 4.0268×10−6/K, 6.4428×10−6/K, 6.5853×10−6/K for KTaO3, KTa0.67Nb0.33O3, and KTa0.63Nb0.37O3, respectively. The density follows an almost linear decrease when the temperature increases = from 298.15 to 773.15 K. The measured specific heats at 303.15 K are: 0.375 J g−1 K−1 for KTaO3; 0.421 J g−1 K−1 for KTa0.67Nb0.33O3, and 0.430 J g−1 K−1 for KTa0.63Nb0.37O3 The thermal diffusion coefficients of the crystals were measured over the temperature range from 303.15−563.15 K. The calculated thermal conductivity values of KTaO3, KTa0.67Nb0.33O3, and KTa0.63Nb0.37O3 at 303.15 K are 8.551, 5.592, and 4.489 W m−1 K−1, respectively. The variation of these thermal properties versus Nb concentration is qualitatively analyzed. These results show that crystalline KTN is a promising material for optical applications.
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65.40.De Thermal expansion; thermomechanical effects
65.40.gd Entropy
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
64.70.dj Melting of specific substances
42.70.-a Optical materials

Bowing of the band gap pressure coefficient in InxGa1−xN alloys

G. Franssen, I. Gorczyca, T. Suski, A. Kamińska, J. Pereiro, E. Muñoz, E. Iliopoulos, A. Georgakilas, S. B. Che, Y. Ishitani, A. Yoshikawa, N. E. Christensen, and A. Svane

J. Appl. Phys. 103, 033514 (2008); http://dx.doi.org/10.1063/1.2837072 (6 pages) | Cited 16 times

Online Publication Date: 8 February 2008

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The hydrostatic pressure dependence of photoluminescence, dEPL/dp, of InxGa1−xN epilayers has been measured in the full composition range 0<x<1. Furthermore, ab initio calculations of the band gap pressure coefficient dEG/dp were performed. Both the experimental dEPL/dp values and calculated dEG/dp results show pronounced bowing and we find that the pressure coefficients have a nearly constant value of about 25 meV/GPa for epilayers with x>0.4 and a relatively steep dependence for x<0.4. On the basis of the agreement of the observed PL pressure coefficient with our calculations, we confirm that band-to-band recombination processes are responsible for PL emission and that no localized states are involved. Moreover, the good agreement between the experimentally determined dEPL/dp and the theoretical curve of dEG/dp indicates that the hydrostatic pressure dependence of PL measurements can be used to quantify changes of the band gap of the InGaN ternary alloy under pressure, demonstrating that the disorder-related Stokes shift in InGaN does not induce a significant difference between dEPL/dp and dEG/dp. This information is highly relevant for the correct analysis of pressure measurements.
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78.55.Cr III-V semiconductors
07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
71.20.Nr Semiconductor compounds

Extremely low temperature growth of ZnO by atomic layer deposition

E. Guziewicz, I. A. Kowalik, M. Godlewski, K. Kopalko, V. Osinniy, A. Wójcik, S. Yatsunenko, E. Łusakowska, W. Paszkowicz, and M. Guziewicz

J. Appl. Phys. 103, 033515 (2008); http://dx.doi.org/10.1063/1.2836819 (6 pages) | Cited 49 times

Online Publication Date: 11 February 2008

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We report on the zinc oxide (ZnO) thin films obtained by the atomic layer deposition (ALD) method using diethyl zinc and water precursors, which allowed us to lower deposition temperature to below 200 °C. The so-obtained “as grown” ZnO layers are polycrystalline and show excitonic photoluminescence (PL) at room temperature, even if the deposition temperature was lowered down to 100 °C. Defect-related PL bands are of low intensity and are absent for layers grown at 140−200 °C. This is evidence that extremely low temperature growth by ALD can result in high quality ZnO thin films with inefficient nonradiative decay channels and with thermodynamically blocked self-compensation processes.
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68.55.ag Semiconductors
81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors

The crystallinity and surface morphology of zinc octaethylporphyrin thin films on an indium-tin-oxide substrate

S. Ryuzaki and J. Onoe

J. Appl. Phys. 103, 033516 (2008); http://dx.doi.org/10.1063/1.2838204 (3 pages) | Cited 3 times

Online Publication Date: 11 February 2008

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The crystallinity and surface morphology of zinc octaethylporphyrin, Zn(OEP), thin films (20 nm thick) deposited on an indium-tin-oxide substrate have been investigated using x-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD and SEM results show that the Zn(OEP) film formed at room temperature (RT) was amorphous and its surface morphology was smooth, whereas the film deposited at 473 K was crystalline and its surface morphology became rough compared to that formed at RT. On the other hand, when the Zn(OEP) film formed at RT was subsequently annealed at 473 K for 1 min, the film was crystallized as well as formed at 473 K but its surface morphology was maintained to be smooth.
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68.55.J- Morphology of films
68.35.bm Polymers, organics
68.35.bg Semiconductors
81.40.Gh Other heat and thermomechanical treatments

Proton irradiation of germanium isotope multilayer structures at elevated temperatures

S. Schneider, H. Bracht, M. C. Petersen, J. Lundsgaard Hansen, and A. Nylandsted Larsen

J. Appl. Phys. 103, 033517 (2008); http://dx.doi.org/10.1063/1.2838206 (5 pages) | Cited 10 times

Online Publication Date: 11 February 2008

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Irradiation of germanium (Ge) isotope heterostructures with 2.5 MeV protons have been performed at 550 °C. The applied proton flux was varied between 1.0 and 1.5 μA leading to various rates of Frenkel pair production. After irradiation, concentration profiles of the Ge isotopes were recorded by means of secondary ion mass spectrometry (SIMS). An inhomogeneous broadening of the isotope structure was observed. In addition to the effect of irradiation enhanced self-diffusion, an influence of the formation of microscopic defects on the detected broadening was ascertained. Atomic force and scanning electron microscopy show that the microscopic defects are most probably resulting from an aggregation of vacancies formed during irradiation. Numerical analysis of Ge profiles not disturbed by microdefect formation indicates a significant contribution of self-interstitials to self-diffusion under irradiation.
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61.72.J- Point defects and defect clusters
61.82.Fk Semiconductors
66.30.Fq Self-diffusion in metals, semimetals, and alloys

Analysis of surface thermal lens signal in optical coatings with top-hat beam excitation

Bincheng Li, Xiaoxiao Chen, and Yuan Gong

J. Appl. Phys. 103, 033518 (2008); http://dx.doi.org/10.1063/1.2841057 (6 pages) | Cited 3 times

Online Publication Date: 13 February 2008

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An explicit theoretical model based on three-dimensional thermal conduction, thermoelasticity, and Fresnel diffraction integral is developed to describe the surface thermal lens (STL) with a continuous-wave (cw) modulated excitation. The surface displacements and STL amplitudes obtained with both top-hat and Gaussian beam excitations are theoretically computed and compared. A STL experiment is performed with the cw modulated top-hat beam excitation to investigate the dependences of the STL amplitude on the experimental parameters, namely, the detection distance, the modulation frequency, the radius of the excitation beam, etc. Good agreements between the experimental and theoretical results are obtained. The results indicate that high sensitivity of the STL technique can be achieved with the top-hat beam excitation and by optimizing the experimental configuration.
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42.79.Wc Optical coatings
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Strain at the surface of GaN epilayers and at GaN/sapphire interface before and after laser lift-off (LLO) from the sapphire substrate

Amal Elgawadi and Jerzy Krasinski

J. Appl. Phys. 103, 033519 (2008); http://dx.doi.org/10.1063/1.2836955 (3 pages) | Cited 2 times

Online Publication Date: 14 February 2008

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Four GaN epilayers were grown on sapphire by hydride vapor phase epitaxy. The lattice and thermal expansion coefficient mismatches between the epilayers and the sapphire produce a strain in the structure. The strain at the surface of the epilayers was estimated using photoluminescence. By analyzing the variation of the surface strain with thickness, the minimum thickness required to obtain low surface strain was estimated to be approximately 45 μm. Furthermore, the strain at the interface of the sapphire and the epilayers was estimated after laser lift-off of GaN epilayers. The analysis showed that a low and almost constant strain at the surface of the interface for the separated samples can be obtained for an epilayer thickness greater than 18 μm.
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81.05.Ea III-V semiconductors
68.35.Gy Mechanical properties; surface strains
78.55.Cr III-V semiconductors
68.60.Bs Mechanical and acoustical properties
68.55.ag Semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
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