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1 Mar 1999

Volume 85, Issue 5, pp. 2465-3011

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Electrostatic force microscopy studies of surface defects on GaAs/Ge films

Q. Xu and J. W. P. Hsu

J. Appl. Phys. 85, 2465 (1999); http://dx.doi.org/10.1063/1.369622 (8 pages) | Cited 27 times

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We apply electrostatic force microscopy (EFM) to study defects in GaAs films grown on Ge. On a GaAs film with surface antiphase boundaries (APBs), we reproducibly measure the surface contact potential (SCP) at the APBs to be (30±5) mV higher than that of the domains, due to the surface Fermi level at APBs being pinned closer to the valence band maximum. On a thick film which contains buried APBs and wedge-shaped depressions on the surface, we find that the SCP of the wedge-shaped depressions is (25±5) mV lower than that of the GaAs surface. Hence, these wedge-shaped depressions have defect electronic states different from those of APBs. The capacitance gradient (∂C/∂z) contrasts on the two samples are also shown to arise from different origins. Factors that can affect the measured SCP and ∂C/∂z values are discussed. We demonstrate a new application of EFM to distinguish different types of defects by measuring variations in relative SCP (thus the work function or position of Fermi level) and/or ∂C/∂z on sample surfaces. The spatial resolutions of SCP and ∂C/∂z are 30 nm, limited by the tip size. © 1999 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.20.At Surface states, band structure, electron density of states
68.35.Ct Interface structure and roughness
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LP01-mode output beam from a micro-sized hollow optical fiber: A simple theoretical model and its applications in atom optics

Jianping Yin and Yifu Zhu

J. Appl. Phys. 85, 2473 (1999); http://dx.doi.org/10.1063/1.369608 (9 pages) | Cited 6 times

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We calculate electric field distributions of the output beam from a LP01 mode in a micro-sized hollow optical fiber under the Fresnel approximation and find that the output beam characteristics in free space is similar to that of a TEM01∗ doughnut laser beam. We propose a simple theoretical model, a modified TEM01∗ doughnut beam, to simulate the free-space output beam from the LP01 mode in hollow fibers, and discuss potential applications of the LP01-mode output beam in atomic guiding, funneling, cooling, and trapping. Our study shows that this model is in good agreement with the numerical results derived from the Fresnel diffraction theory (except near the weak first-order diffraction ring around the zero-order diffraction peak). The model can be conveniently used to calculate the optical potential, gradient force, light-induced acceleration, spontaneous-emission rate, and quantum tunneling loss in atomic guiding, funneling, and trapping with the LP01-mode output beam in free space. It can be also used to study the optical-potential evaporative cooling of cold atoms in a gravito-optical trap constructed by the LP01-mode output beam. © 1999 American Institute of Physics.
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42.81.-i Fiber optics
03.75.Be Atom and neutron optics
41.85.-p Beam optics
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
37.10.De Atom cooling methods
37.10.Gh Atom traps and guides

High-performance photorefractivity in high- and low-molar-mass liquid crystal mixtures

Hiroshi Ono and Nobuhiro Kawatsuki

J. Appl. Phys. 85, 2482 (1999); http://dx.doi.org/10.1063/1.369609 (6 pages) | Cited 19 times

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High-performance photorefractivity in a thick-grating regime was observed in high- (H-LC) and low-molar-mass liquid crystal (L-LC) mixtures (HL-LCMs) doped with fullerene. The photorefractive performance strongly depended on the concentration ratio of H-LC and L-LC. A high net gain coefficient over 600 cm−1 was achieved with low applied dc fields (0.7 V/μm) and a fringe spacing of 2.8 μm. The gain coefficients and the resolution increased with increasing the concentration of the H-LCs. The photorefractive grating formation time was varied between 0.12 and 3.5 s, which depended on the concentration of the H-LCs. © 1999 American Institute of Physics.
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42.70.Df Liquid crystals
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.40.Eq Holographic optical elements; holographic gratings
64.75.-g Phase equilibria
78.20.Jq Electro-optical effects
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Thermal analysis of a laser pulse for discrete spot surface transformation hardening

Paul R. Woodard and John Dryden

J. Appl. Phys. 85, 2488 (1999); http://dx.doi.org/10.1063/1.369610 (9 pages) | Cited 6 times

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Conventional laser transformation hardening is achieved by scanning a laser beam over a surface to raise the temperature above the austenitizing temperature and allowing self quenching to form martensite. A new approach, developed at the National Research Council of Canada’s Integrated Manufacturing Technologies Institute, uses discrete pulses to create a series of hardened “spots.” Unfortunately, existing transformation hardening models do not apply to this case due to the traditional assumption of a scanning velocity. For this reason, new predictive tools must be developed. An analytical solution to the axisymmetric heat conduction under a Gaussian energy distribution is presented which can be used to calculate the temperature distribution from a short laser pulse. The method is also used to calculate the size of a transformation hardened spot under the incident energy of a stationary laser.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
81.30.Kf Martensitic transformations
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
64.70.K- Solid-solid transitions
81.70.Pg Thermal analysis, differential thermal analysis (DTA), differential thermogravimetric analysis

Phase-matched optical second-harmonic generation in GaN and AlN slab waveguides

D. N. Hahn, G. T. Kiehne, J. B. Ketterson, G. K. L. Wong, P. Kung, A. Saxler, and M. Razeghi

J. Appl. Phys. 85, 2497 (1999); http://dx.doi.org/10.1063/1.369611 (5 pages) | Cited 8 times

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Phase-matched optical second-harmonic (SH) generation was observed in GaN and AlN slab waveguides. Phase matching was achieved by waveguide modal dispersion. By tuning the output wavelength of an optical parametric amplifier, several phased-matched SH peaks were observed in the visible spectrum covering blue to red wavelengths. The peak positions are in agreement with the values calculated using the dispersive refractive indices of the film and substrate materials. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Nv Optical frequency converters
42.79.Gn Optical waveguides and couplers
42.65.Yj Optical parametric oscillators and amplifiers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Er3+:Yb3+ codoped lead fluoroindogallate glasses for mid infrared and upconversion applications

D. F. de Sousa, L. F. C. Zonetti, M. J. V. Bell, R. Lebullenger, A. C. Hernandes, and L. A. O. Nunes

J. Appl. Phys. 85, 2502 (1999); http://dx.doi.org/10.1063/1.369612 (6 pages) | Cited 38 times

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In this work, two sets of lead fluoroindogallate glasses were studied with the aim of using them as active media for laser devices at the mid infrared (∼2.8 μm) and visible (∼0.54 μm) regions. The infrared and upconverted emissions of Er3+ in single and Er3+:Yb3+ codoped samples were analyzed, and it was observed that the best set of samples for 2.8 μm emission was the single doped one, and that as the upconversion (anti-Stokes luminescence) increased as a function of Yb3+ concentration, the infrared emission decreased in the same manner. The results suggest that the codoping with Yb3+ favors only the upconversion processes which depopulate the 4I11/2 level, reducing the 2.8 μm emission intensity. On the other hand, the Yb3+ codoping will certainly increase the efficiency of an upconversion based device. Quantum efficiencies of infrared emissions and radiative lifetimes were calculated by using the Judd–Ofelt approximation. Er3+–Er3+ and Er3+–Yb3+ energy transfer efficiencies were calculated using the measured lifetimes of the levels involved in the energy transfer processes. © 1999 American Institute of Physics.
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42.70.Ce Glasses, quartz
42.70.Hj Laser materials
78.55.Hx Other solid inorganic materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.55.Rz Doped-insulator lasers and other solid state lasers

Elastic activity of the chiral medium

Ruyen Ro

J. Appl. Phys. 85, 2508 (1999); http://dx.doi.org/10.1063/1.369613 (6 pages) | Cited 5 times

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Chiral materials are noncentrosymmetric due to handedness in their microstructures. The elastic field behavior in a chiral medium is readily described herein using the governing equations and constitutive relations for noncentrosymmetric, isotropic micropolar materials. Accordingly, linearly polarized longitudinal waves and left and right circularly polarized transverse waves are eigenstates for elastic waves in the chiral medium. Consequently, by using appropriate field representations along with prescribed boundary conditions, scattering characteristics at chiral interfaces can be readily determined. In this paper, transmission characteristics, i.e., magnitudes and rotation angles, of the chiral slab bounded by achiral media for normally incident transverse waves are the focus of this investigation. Simulation results show the Cotton effect in the magnitude and rotation angle curves, verifying theoretically the elastic activity of a chiral medium.© 1999 American Institute of Physics.
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46.25.Cc Theoretical studies

Impluse response of a fiber optic probe hydrophone determined with shock waves in water

Z. Q. Wang, P. Lauxmann, C. Wurster, M. Köhler, B. Gompf, and W. Eisenmenger

J. Appl. Phys. 85, 2514 (1999); http://dx.doi.org/10.1063/1.369569 (3 pages) | Cited 10 times

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The impluse response of a fiber optic probe hydrophone (FOPH) is determined through it’s step response obtained by using a self-focusing electromagnetic shock wave excitation. The experimental transfer function agrees well with the theoretical calculation of the transient response by diffraction of the acoustic wave at the fiber end face. A rise time of about 5 ns has been obtained for the shock front of the self-focusing shock wave generator by the deconvolution of the output signal of the hydrophone with it’s impulse response. The FOPH can be used as a standard hydrophone for the absolute wideband measurement of shock waves of lithotripters and of acoustic waves in liquids in general.© 1999 American Institute of Physics.
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43.30.Yj Transducers and transducer arrays for underwater sound; transducer calibration
43.38.Pf Hydroacoustic and hydraulic transducers
43.58.Gn Acoustic impulse analyzers and measurements
07.60.Vg Fiber-optic instruments
43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
62.50.-p High-pressure effects in solids and liquids
43.40.Jc Shock and shock reduction and absorption
42.81.Pa Sensors, gyros
62.60.+v Acoustical properties of liquids
92.10.Vz Underwater sound

Picosecond thermal pulses in thin metal films

M. A. Al-Nimr and V. S. Arpaci

J. Appl. Phys. 85, 2517 (1999); http://dx.doi.org/10.1063/1.369568 (5 pages) | Cited 25 times

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A simplified approach is introduced to describe the thermal behavior of a thin metal film exposed to picoseconds thermal pulses. The approach is based on the assumption that the metal film thermal behavior occurs in two separate stages. In the first stage, electron gas transmits its energy to the solid lattice through electron-phonon coupling and other mechanisms of energy transport are negligible. In the second stage, electron gas and solid lattice are in thermal equilibrium, the energy transfer through electron-phonon coupling is negligible, and thermal diffusion dominates. The proposed approach eliminates the coupling between the energy equations and the reduced differential equations are easier to handle. The proposed approach applies to metal films whenever GL2/Ke≫1. © 1999 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
63.20.K- Phonon interactions
66.30.Fq Self-diffusion in metals, semimetals, and alloys

Sheath and presheath potentials for anode, cathode and floating plasma-facing surfaces

K. F. Stephens and C. A. Ordonez

J. Appl. Phys. 85, 2522 (1999); http://dx.doi.org/10.1063/1.369845 (6 pages) | Cited 8 times

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Simple expressions for sheath and presheath potentials are provided for anode, cathode and electrically floating plasma-facing surfaces. The expressions are developed using a fully kinetic theory that includes the effects of secondary or thermionic electron emission from the plasma-facing surface. The emission can be space-charge limited and a criterion is provided for the onset of space-charge saturation. © 1999 American Institute of Physics.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Dg Plasma kinetic equations

Experimental investigation of surface wave propagation in collisional plasma columns

F. M. Dias, E. Tatarova, J. Henriques, and C. M. Ferreira

J. Appl. Phys. 85, 2528 (1999); http://dx.doi.org/10.1063/1.369570 (6 pages) | Cited 15 times

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An experimental study of surface wave propagation in a low-pressure collisional plasma column generated by the wave itself is presented. It is experimentally demonstrated that the maximum wave number value attainable decreases with increasing collisional effects. The separate effects of collisions and radial plasma inhomogeneity on the wave propagation are investigated. Some practical considerations concerning the correct measurement of the phase and attenuation diagrams are pointed out. © 1999 American Institute of Physics.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

Monte Carlo simulation study of the scaling of electron transport parameters in crossed dc electric and magnetic fields

Satoru Nakamura, Peter L. G. Ventzek, and Kazutaka Kitamori

J. Appl. Phys. 85, 2534 (1999); http://dx.doi.org/10.1063/1.369571 (6 pages) | Cited 4 times

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A Monte Carlo computational experiment is used to study the scaling of electron swarm parameters in crossed direct current electric and magnetic fields in argon and methane. The ranges of reduced electric and magnetic fields investigated are 28–2830 Td and 10 G/Torr–10000 G/Torr, respectively. Significant deviation from classical scaling is observed and characterized. For very high magnetic fields, some swarm parameters (mean energy and total collision frequency) become insensitive to the magnetic field variations. In addition, when swarm parameters are characterized in terms of their mean electron energy, for some ranges of mean electron energy, the correlation between a parameter and the reduced magnetic field strength can disappear. The impact of these results is discussed in terms of controlling the plasma chemistry via the magnetic field. © 1999 American Institute of Physics.
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52.25.Fi Transport properties
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.65.Pp Monte Carlo methods

Gas dynamics and electromagnetic processes in high-current arc plasmas. Part I. Model formulation and steady-state solutions

Lei Z. Schlitz, Suresh V. Garimella, and S. H. Chan

J. Appl. Phys. 85, 2540 (1999); http://dx.doi.org/10.1063/1.369572 (7 pages) | Cited 20 times

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A three-dimensional computational model has been developed to study the effects of self-induced and external magnetic fields, as well as gassing effects, on arcs involved in switching devices. A commercial computational fluid dynamics code has been adapted and modified to model the fully coupled plasma flow, heat transfer, and electromagnetic field. In this paper, a model is developed to analyze a steady-state, two-dimensional axisymmetric air arc column at low current levels under conditions in which the effects of the self-induced magnetic field are negligible. The model is then extended to analyze a three-dimensional arc column at high current levels with the inclusion of self-induced magnetic effects. The effects of cathode size, distance from the electrode, current level, self-induced magnetic field, and natural convection on the arc plasma are investigated. Predictions from these models compare favorably with published analytical and experimental results. The influence of external transverse magnetic fields, as well as the presence of gassing materials, on a three-dimensional arc column in both steady-state and transient situations will be discussed in L. Z. Schlitz et al. [J. Appl. Phys. 85, 2547 (1999)]. © 1999 American Institute of Physics.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.30.-q Plasma dynamics and flow
52.65.-y Plasma simulation

Gas dynamics and electromagnetic processes in high-current arc plasmas. Part II. Effects of external magnetic fields and gassing materials

Lei Z. Schlitz, Suresh V. Garimella, and S. H. Chan

J. Appl. Phys. 85, 2547 (1999); http://dx.doi.org/10.1063/1.369573 (9 pages) | Cited 16 times

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Arc plasmas in switching devices are investigated in the presence of external and self-induced magnetic fields, as well as of gassing materials, using a three-dimensional computational model. The model development and validation for two- and three-dimensional arc columns with a self-induced magnetic field and natural-convection effects was presented in L. Z. Schlitz et al. [J. Appl. Phys. 85, 2540 (1999)]. The present paper discusses further development of the model to enable an investigation of the effects of external magnetic fields and the presence of gassing materials. Steady-state solutions with an external transverse magnetic field (0–20 mT) imposed on a wall-stabilized air arc column are presented, followed by a study of the transient response of the arc in an open-ended arc chamber in a 0.68 ms time span. Ablation from the side walls of the arc chamber made of gassing materials (and the resulting mixing of hydrogen and air) is shown to increase the arc voltage dramatically due to the increase in heat transfer around the arc body. © 1999 American Institute of Physics.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.30.-q Plasma dynamics and flow
52.65.-y Plasma simulation
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Control of the bias tilt angles in nematic liquid crystals

S. V. Yablonskii, K. Nakayama, S. Okazaki, M. Ozaki, K. Yoshino, S. P. Palto, M. Yu. Baranovich, and A. S. Michailov

J. Appl. Phys. 85, 2556 (1999); http://dx.doi.org/10.1063/1.369574 (6 pages) | Cited 4 times

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The pretilt angle controlled by electric field was studied by the modulation ellipsometry technique. The easy direction of compensated nematic liquid crystals was controlled by surface flexoelectric torque created by the linear coupling of the director deformation and electric field. The weak anchoring energy necessary for the occurrence of flexoelectric distortion was produced by unidirectional rubbing of the clean indium–tin–oxide covered glasses with a cotton cloth. The pretilt angle was measured as a function of electric field. Long relaxation times of the optical response (hundreds of seconds) were observed. The rubbed thin polyvinyl alcohol and polyimide aligning layers were seen to promote strong anchoring energy (>0.5 erg/cm2) preventing any deviation of pretilt angle and, consequently, to suppress the optical response. The probable applications of the obtained results are discussed. © 1999 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
77.65.-j Piezoelectricity and electromechanical effects
78.20.Jq Electro-optical effects

Hydrogen interaction with implantation induced point defects in p-type silicon

S. Fatima, C. Jagadish, J. Lalita, B. G. Svensson, and A. Hállen

J. Appl. Phys. 85, 2562 (1999); http://dx.doi.org/10.1063/1.369575 (6 pages) | Cited 13 times

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Interaction of hydrogen with implantation induced point defects in p-type Si has been monitored using deep level transient spectroscopy. H ions are implanted into p-Si using low doses in the range from 109 to 1010 cm−2. Vacancy and interstitial related defects are observed. Besides irradiation induced defects with levels at Ev+0.19 and Ev+0.35 eV, two additional defect levels at 0.28 and 0.51 eV above the valence band edge (Ev) are resolved. They are identified as hydrogen related after comparison with He, B, and C implanted p-type Si. The generation of these defect levels, in the presence of hydrogen, has been studied as a function of ion dose, sample depth, and impurity content in the as grown Si. The level at Ev+0.19 eV shows a saturation effect for higher hydrogen doses. This is attributed to passivation by mobile hydrogen through the formation of neutral complexes. The level at Ev+0.51 eV has been assigned to be a complex involving H and B interstitials. © 1999 American Institute of Physics.
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71.55.Cn Elemental semiconductors
61.72.J- Point defects and defect clusters
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology

Infrared and transmission electron microscopy studies of ion-implanted H in GaN

C. H. Seager, S. M. Myers, G. A. Petersen, J. Han, and T. Headley

J. Appl. Phys. 85, 2568 (1999); http://dx.doi.org/10.1063/1.369623 (6 pages) | Cited 10 times

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H and D have been implanted into undoped films of GaN heteroepitaxially grown on sapphire over a dose range from 5×1015 to 5×1017 ions/cm2. After a 600 °C post-implantation anneal, room temperature Fourier-transform-infrared spectroscopy reveals two major local vibrational modes at 3183 cm−1 (2364 cm−1) and 3219 cm−1 (2386 cm−1) for the H (D) material implanted at higher doses. The position and isotope shift (1.35) of these modes strongly suggest they are due to hydrogen bonded to nitrogen atoms; these atoms are located on the surfaces of seven sided cavities created by the H implant and thermal anneal cycle and identified by transmission electron microscopy. Nuclear reaction analyses of isochronally annealed D implanted films indicate that most of the deuterium remains bound within the implanted layer, and that the major release stage for D occurs near 900 °C. By contrast, the N–H (N–D) vibrational modes anneal out in the 750–800 °C temperature range. These findings indicate that the bound H exists in at least two major states, believed to be IR-active N–H on the cavity walls and IR-inactive H2 gas within the cavities. © 1999 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
63.20.Pw Localized modes
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing

Infrared vibration spectra of hydrogenated, deuterated, and tritiated amorphous silicon

L. S. Sidhu, T. Kosteski, S. Zukotynski, and N. P. Kherani

J. Appl. Phys. 85, 2574 (1999); http://dx.doi.org/10.1063/1.369607 (5 pages) | Cited 17 times

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This article presents infrared absorption data of amorphous silicon alloys in which the hydrogen isotopes deuterium and tritium have been substituted for hydrogen. Silicon–deuterium and silicon–tritium vibration frequencies are related to silicon–hydrogen vibration frequencies by simple mass relationships. The silicon–deuterium wagging vibration is broadened and blueshifted due to strong coupling to the amorphous silicon network vibrations. © 1999 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
78.30.Am Elemental semiconductors and insulators
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Lattice thermal conductivity of wires

S. G. Walkauskas, D. A. Broido, K. Kempa, and T. L. Reinecke

J. Appl. Phys. 85, 2579 (1999); http://dx.doi.org/10.1063/1.369576 (4 pages) | Cited 50 times

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The lattice thermal conductivity of free standing wires is calculated within a Boltzmann equation approach. Diffusive and specular phonon scattering at the wire surfaces are included by appropriate boundary conditions on the phonon distribution. The wire thermal conductivity is found to decrease markedly below the bulk value for narrow wires. We show that this decrease in wires is larger than that which occurs in free standing wells of comparable size. © 1999 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
63.20.K- Phonon interactions
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Texture analysis of damascene-fabricated Cu lines by x-ray diffraction and electron backscatter diffraction and its impact on electromigration performance

Linda Vanasupa, Young-Chang Joo, Paul R. Besser, and Shekhar Pramanick

J. Appl. Phys. 85, 2583 (1999); http://dx.doi.org/10.1063/1.369624 (8 pages) | Cited 43 times

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The texture of electroplated Cu lines of 0.375, 0.5 and 1.5 μm widths with Ta and TiN barrier layers was analyzed using x-ray pole figure and electron backscatter diffraction (EBSD) techniques. Both techniques indicate a strong (111) fiber texture relative to the bottom surface of the trench for samples with a Ta barrier layer and a 400 °C, 30 min, postelectroplating anneal. Samples with a TiN barrier and no anneal exhibit a weak (111) texture. For both barrier layers the quality of the texture, as measured by (111) peak intensity, fraction of randomly oriented grains and (111) peak width, degrades with decreasing linewidth. EBSD data also indicate (111) texture relative to the sidewalls of the trench in samples with a Ta barrier and postelectroplating anneal. Electromigration tests at 300 °C of 0.36 μm damascene Cu lines with the same process conditions show that samples with very weak (111) texture have median time to failures that exceed those of the strongly textured Cu lines. These results indicate that diffusion at interfaces, such as the Cu/barrier and Cu/overlayer interfaces, along with diffusion along an electroplating seam play more dominant roles in electromigration failure in damascene-fabricated lines than diffusion along grain boundaries within the interconnect. © 1999 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
68.55.-a Thin film structure and morphology
66.30.Qa Electromigration
81.05.Bx Metals, semimetals, and alloys
81.15.Pq Electrodeposition, electroplating
79.20.Kz Other electron-impact emission phenomena
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Growth of self-organized GaSb islands on a GaAs surface by molecular beam epitaxy

T. Wang and A. Forchel

J. Appl. Phys. 85, 2591 (1999); http://dx.doi.org/10.1063/1.369625 (4 pages) | Cited 13 times

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We systematically investigated the growth of self-organized GaSb islands on a GaAs surface by molecular beam epitaxy technique. The lattice mismatch between GaAs and GaSb is 7.8%. At low growth temperature, only one kind of island can be observed, which is thought to be issued from the nucleation cluster. When the growth temperature is increased, another kind of island appears due to coalescence. When the growth temperature is above 535 °C, only the latter can be observed. From the temperature dependence of island density and size, surface diffusion energy and activation energy of GaSb on a GaAs surface have been determined to be 0.85 and 2.15 eV, respectively. © 1999 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors
68.35.Fx Diffusion; interface formation
68.35.B- Structure of clean surfaces (and surface reconstruction)

Structural, optical, and surface acoustic wave properties of epitaxial ZnO films grown on (01math2) sapphire by metalorganic chemical vapor deposition

C. R. Gorla, N. W. Emanetoglu, S. Liang, W. E. Mayo, Y. Lu, M. Wraback, and H. Shen

J. Appl. Phys. 85, 2595 (1999); http://dx.doi.org/10.1063/1.369577 (8 pages) | Cited 292 times

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High-quality ZnO films are receiving increased interest for use in low-loss high-frequency surface acoustic wave (SAW) devices, acousto-optic and optical modulators, as buffer layers for III-nitride growth, and as the active material in ultraviolet solid state lasers. In this work, high quality epitaxial ZnO films were grown on R-plane sapphire substrates by metalorganic chemical vapor deposition. The structural, piezoelectric, and optical properties of the ZnO films on R sapphire have been investigated. The epitaxial relationship between ZnO and R-Al2O3 was found to be (11math0) ZnO∥(01math2) Al2O3, and [0001] ZnO∥[0math11] Al2O3. The interface between as-grown ZnO and R sapphire was atomically sharp and semicoherent, as evaluated by transmission electron microscopy. On annealing the films at temperatures above 850 °C, a solid state reaction occurred between ZnO and Al2O3, resulting in the formation of ZnAl2O4 (spinel) at the interface. A 15–20 nm spinel layer formed when the ZnO film was annealed at 850 °C for 30 min, whereas a 150 nm layer formed when the film was annealed at 1000 °C for 150 min. To prevent this reaction from occurring, the maximum process temperature should be below 750 °C. The surface acoustic wave properties of the piezoelectric ZnO were evaluated by fabricating SAW devices on (11math0) ZnO/(01math2) Al2O3. An effective electromechanical coupling coefficient, keff2, of 6% was achieved for a 1.5 μm thick ZnO film, which is close to the value for bulk single-crystal ZnO. The photoluminescence spectra were obtained both at room temperature and at 11 K. The full width at half maximum of the 3.363 eV band edge emission photoluminescence peak measured at 11 K was 6 meV, which is close to that for single-crystal ZnO. We also evaluated the anisotropic absorption characteristics of the (11math0) ZnO film, which can be used for a high contrast ultraviolet light modulator. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Et II-VI semiconductors
78.40.Fy Semiconductors
42.79.Jq Acousto-optical devices
42.79.Hp Optical processors, correlators, and modulators
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
68.60.Dv Thermal stability; thermal effects
68.60.Bs Mechanical and acoustical properties

Microstructure evolution of GaSe thin films grown on GaAs(100) by molecular beam epitaxy

Z. R. Dai, S. R. Chegwidden, L. E. Rumaner, and F. S. Ohuchi

J. Appl. Phys. 85, 2603 (1999); http://dx.doi.org/10.1063/1.369578 (6 pages) | Cited 8 times

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GaSe thin films were grown on a GaAs(100) substrate by molecular beam epitaxy. Microstructures of the thin films and interface were characterized by transmission electron microscopy. The dominant polytype formed in the GaSe thin films was a γ type, which has a 3R-rhombohedral structure with R3m space group. Predominant crystallographic orientation between the GaSe thin films and the GaAs substrate was characterized as: [math100]GaSe‖[011]GaAs/(0001)GaSe‖(100)GaAs. In addition, GaSe thin films with orientation of [math2math0]GaSe‖[011]GaAs/(0001)GaSe‖(100)GaAs can also grow in some local areas. The interface between GaSe thin films and GaAs substrate constitutes thin intermediate layers of a vacancy ordered β-Ga2Se3, the structure of which inherits the crystallographic features of the GaAs(100) surface. Mechanisms responsible for formation of the preferable crystallographic orientation in the GaSe thin films in the initial growth stage are suggested. © 1999 American Institute of Physics.
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81.05.Hd Other semiconductors
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Structural evolution during deposition of epitaxial Fe/Pt(001) multilayers

T. C. Hufnagel, M. C. Kautzky, B. J. Daniels, and B. M. Clemens

J. Appl. Phys. 85, 2609 (1999); http://dx.doi.org/10.1063/1.369636 (8 pages) | Cited 17 times

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We have investigated the structure of epitaxial Fe/Pt(001) multilayers deposited by direct current magnetron sputtering. In these multilayers, the structure of the Fe layers depends on their thickness: Thick (tFe>22 Å) Fe layers are body-centered cubic (bcc), while thin (tFe<12 Å) Fe layers are face-centered cubic (fcc). Ex situ x-ray diffraction reveals that the unstrained lattice parameter of bcc Fe in epitaxial multilayers is significantly greater than that of bulk bcc Fe, possibly due to alloying with Pt. This suggests that the observed “fcc Fe” is actually an intermixed fcc Fe–Pt interfacial layer. To investigate this possibility, we have performed grazing-incidence x-ray scattering in situ during deposition of epitaxial Fe/Pt(001) multilayers. The structure of Fe(001) layers as thin as 10 Å is bcc, strained due to epitaxial mismatch with the Pt(001) underlayer. Additional Fe deposition results in relaxation of the bcc Fe lattice parameter toward its bulk value. Deposition of Pt onto a 50 Å thick bcc Fe(001) layer has little effect on the Fe, other than to increase its lattice parameter slightly. In contrast, deposition of Pt onto a 20-Å-thick bcc Fe(001) layer results in a partial transformation of the Fe to a fcc structure. We propose that this transformation is the result of intermixing of Pt into the previously deposited Fe layer, resulting in the formation of a fcc Fe-Pt alloy layer. © 1999 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
75.30.Gw Magnetic anisotropy

In situ characterization of titanium silicide formation: The effect of Mo interlayer, temperature ramp-rate, and annealing atmosphere

S.-L. Zhang, C. Lavoie, C. Cabral, J. M. E. Harper, F. M. d’Heurle, and J. Jordan-Sweet

J. Appl. Phys. 85, 2617 (1999); http://dx.doi.org/10.1063/1.369626 (10 pages) | Cited 22 times

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The formation of titanium silicides has been studied using simultaneous in situ x-ray diffraction with millisecond time resolution and sheet resistance measurements. The effect of a Mo interposed layer between Ti films and Si substrate was investigated by varying the thickness of the Mo interlayer from 0 (Ti/Si) to 1.8 nm (Ti/Mo/Si). The thickness of Ti was kept to 55 nm for all samples. Both isothermal annealing and ramp annealing in helium were performed in order to study the mechanism of silicide formation. While C49 TiSi2 was the only disilicide found after annealing Ti/Si at 650 °C for 20 min, C54 TiSi2 was readily formed in the presence of Mo. The formation of C49 TiSi2 was not observed with a 1.8 nm thick Mo interlayer. Instead, there was indication that C40 (Mo,Ti)Si2 was formed. In addition, broad diffraction peaks, weak in intensity, could be all assigned to Ti5Si4. However, the presence of Ti5Si4 alone did not induce the formation of C54 TiSi2. Even with a 20 °C increase in isothermal annealing temperature to 670 °C for 20 min, the presence of Mo was found to be a necessity for the formation of C54 TiSi2. When annealed in nitrogen, instead of helium, the formation of surface titanium nitride competes with the formation of silicides. The formation of C54 TiSi2 was even suppressed in the sample with a 1.8 nm Mo interlayer when annealed at 650 °C in nitrogen. The formation of Ti5Si4 and the role it plays in the formation of other silicides (C40, C49, and C54) are discussed on the basis of simple crystallographic considerations. The effect of a Mo interlayer and/or ramp-rate on the formation of C40 (Mo,Ti)Si2 and C49 TiSi2 is discussed in conjunction with variations of the preferential orientation of C54 TiSi2 films. © 1999 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
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