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1 Sep 2007

Volume 102, Issue 5, Articles (05xxxx)

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Improvement of laser gain by microdomain compensation effects in Nd:SrBa(Nb3O)2 lasers

P. Molina, E. Martín Rodríguez, J. García Solé, L. E. Bausa, D. Jaque, and A. A. Kamisnkii

J. Appl. Phys. 102, 053101 (2007); http://dx.doi.org/10.1063/1.2775916 (4 pages) | Cited 1 time

Online Publication Date: 5 September 2007

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The laser performance of poled and unpoled neodymium-doped strontium barium niobate crystals has been compared. We have found that the random distribution of microferroelectric domains, characteristic of as-grown crystals, leads to a relevant improvement in the laser performance. From the analysis of the optical distortion effects induced by both poled and unpoled crystals we have concluded that the compensation effects taking place between adjacent microdomains inside the active volume are at the origin of this improvement.
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42.55.Rz Doped-insulator lasers and other solid state lasers
77.80.Dj Domain structure; hysteresis

Photoinduced anisotropic response of azobenzene chromophore functionalized multiwalled carbon nanotubes

Yiyu Feng, Wei Feng, Hideki Noda, Akihiko Fujii, Masanori Ozaki, Katsumi Yoshino, and Katsumi Yoshino

J. Appl. Phys. 102, 053102 (2007); http://dx.doi.org/10.1063/1.2776220 (5 pages) | Cited 3 times

Online Publication Date: 7 September 2007

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Azobenzene chromophore covalently functionalized multiwalled carbon nanotubes (AZO-MWCNT) were synthesized and their optical properties were investigated by ultraviolet-visible absorption and photoluminescence spectroscopy. The polarized absorption of the AZO-MWCNT film was measured by cross-polarized light along the directions parallel and perpendicular to the incident light under the irradiation of polarized ultraviolet light. Photoinduced optical anisotropy of the AZO-MWCNT film was dominated by the enhanced dipole transition of the nanotube axis parallel to the incident light and the decreased transition perpendicular to light. The unique anisotropy induced by the photo-orientation of azobenzene chromophore provides insight into the polarized optical properties of carbon nanotubes.
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78.66.Tr Fullerenes and related materials
78.55.Hx Other solid inorganic materials
78.40.Ri Fullerenes and related materials

Modeling light propagation in photonic crystal devices: Simplification of the Bloch mode scattering matrix method

Gah-Yi Vahn, T. P. White, M. J. Steel, C. M. de Sterke, K. Dossou, and L. C. Botten

J. Appl. Phys. 102, 053103 (2007); http://dx.doi.org/10.1063/1.2776372 (7 pages) | Cited 1 time

Online Publication Date: 7 September 2007

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We derive semianalytic models of two types of photonic crystal resonators by simplifying the Bloch mode scattering matrix method. Essential to the models are two parameters, which are interpreted to be the phase change upon reflection and the measure of orthogonality between modes of adjacent waveguides. The models can predict the resonance position to better than 0.02% and the full width at half maximum to within 10%.
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42.70.Qs Photonic bandgap materials
42.25.Fx Diffraction and scattering
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Polarization characteristics of photonic quantum ring laser with three-dimensional whispering gallery resonances

D. K. Kim, S.-J. An, E. G. Lee, and O’Dae Kwon

J. Appl. Phys. 102, 053104 (2007); http://dx.doi.org/10.1063/1.2777121 (3 pages) | Cited 4 times

Online Publication Date: 10 September 2007

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We report polarization characteristics of light from a photonic quantum ring (PQR) laser of three-dimensional (3D) whispering gallery modes. The 3D polarization states of light from the PQR laser were studied with a home-built solid-angle scanner capable of detecting the spatial intensity distribution in a wide range of solid angles. The analysis shows that the dominant polarization vectors of the PQR laser emitting in the surface normal direction lie always tangential to the PQR perimeter, which means there is a strong carrier-photon coupling.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Long-range surface plasmon-polariton waveguides in silica

Pierre Berini

J. Appl. Phys. 102, 053105 (2007); http://dx.doi.org/10.1063/1.2777126 (8 pages) | Cited 11 times

Online Publication Date: 10 September 2007

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Metal stripe waveguides in silica, operating in the fundamental long-range mode and at optical free-space wavelengths near 1550 nm, are discussed in detail. Straight and curved waveguides having various stripe geometries are modeled. Au, Ag, and Al are compared as metals for the stripe. The wavelength response of waveguides is computed. The impact of index asymmetry is determined and discussed. The results generated and collected herein should be useful to the design of low-loss metal stripe waveguides for integrated plasmonic applications in silica and cladding materials of comparable index.
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42.82.Et Waveguides, couplers, and arrays
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Nitrogen incorporation and optical studies of GaAsSbN/GaAs single quantum well heterostructures

Kalyan Nunna, S. Iyer, L. Wu, J. Li, S. Bharatan, X. Wei, R. T. Senger, and K. K. Bajaj

J. Appl. Phys. 102, 053106 (2007); http://dx.doi.org/10.1063/1.2777448 (8 pages) | Cited 1 time

Online Publication Date: 11 September 2007

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In this work, the effects of N incorporation on the optical properties of GaAsSbN/GaAs single quantum wells (SQWs) have been investigated using temperature, excitation, and magnetic dependencies of photoluminescence (PL) characteristics. These layers were grown in an elemental solid source molecular beam epitaxy system with a rf plasma N source. The N concentrations in the range of 0.5%–2.5% were investigated in this study. The SQW with N ∼ 0.5% exhibits a behavior similar to that in an intermediate regime where the contributions from the localized states in the band gap are dominant. The temperature and excitation dependencies of the PL characteristics indicate that for the N concentration of 0.9% and above, the alloy behavior is analogous to that of a regular alloy and the changes in optical properties are only marginal. The conduction band effective mass (meff) values computed from the magnetophotoluminescence spectra using a variational formalism and the band anticrossing model are in good agreement and indicate enhanced values of meff. However, there is no significant variation in meff values of QWs for N ≥ 0.9%. Small redshift of about 30–50 meV for the temperature variations from 10 to 300 K in conjunction with unusually small blueshift observed in the excitation dependence of PL for N ≥ 0.9% indicate that this system holds a great promise for laser applications at 1.55 μm and beyond.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
73.21.Fg Quantum wells
78.20.Ls Magneto-optical effects
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Movement of oxygen vacancies in oxide film during annealing observed by an optical reflectivity difference technique

Xu Wang, Kuijuan Jin, Hubin Lu, Yiyan Fei, Xiangdong Zhu, and Guozhen Yang

J. Appl. Phys. 102, 053107 (2007); http://dx.doi.org/10.1063/1.2776375 (5 pages) | Cited 4 times

Online Publication Date: 14 September 2007

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The monolayer growth of Nb-doped SrTiO3 on SrTiO3 (100) substrate is prepared by a pulsed laser deposition method. The growth and annealing of the film in vacuum and in oxygen ambient are monitored in real time by an oblique-incidence optical reflectivity difference (OIRD) technique and reflection high-energy electron diffraction technique. The films annealed in different ambient result in different optical annealing signals. From the comparison of experimental OIRD signals with the simulation of OIRD signals, we prove that the optical technique can easily tell whether the oxygen vacancies are moving into or moving out of the film during the annealing. The optical signals are found to be composed of contributions from step edges and terraces.
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61.72.J- Point defects and defect clusters
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing
78.66.Li Other semiconductors

Physics of zinc vaporization and plasma absorption during CO2 laser welding

A. K. Dasgupta, J. Mazumder, and P. Li

J. Appl. Phys. 102, 053108 (2007); http://dx.doi.org/10.1063/1.2777132 (15 pages) | Cited 7 times

Online Publication Date: 14 September 2007

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A number of mathematical models have been developed earlier for single-material laser welding processes considering one-, two-, and three-dimensional heat and mass transfers. However, modeling of laser welding of materials with multiple compositions has been a difficult problem. This paper addresses a specific case of this problem where CO2 laser welding of zinc-coated steel, commonly used in automobile body manufacturing, is mathematically modeled. The physics of a low boiling point material, zinc, is combined with a single-material (steel) welding model, considering multiple physical phenomena such as keyhole formation, capillary and thermocapillary forces, recoil and vapor pressures, etc. The physics of laser beam–plasma interaction is modeled to understand the effect on the quality of laser processing. Also, an adaptive meshing scheme is incorporated in the model for improving the overall computational efficiency. The model, whose results are found to be in close agreement with the experimental observations, can be easily extended for studying zinc-coated steel welding using other high power, continuous wave lasers such as Nd:YAG and Yb:YAG.
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81.20.Vj Joining; welding
42.62.Cf Industrial applications
52.77.-j Plasma applications

Optical response and electronic structure of Zn-doped MgAl2O4

K. Izumi, T. Mizokawa, and E. Hanamura

J. Appl. Phys. 102, 053109 (2007); http://dx.doi.org/10.1063/1.2777528 (5 pages) | Cited 3 times

Online Publication Date: 14 September 2007

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We have studied the optical response and the electronic structure of Zn-doped MgAl2O4 using optical transmission, emission, and excitation spectroscopies, x-ray photoemission spectroscopy, and unrestricted Hartree-Fock calculation. Emission lines at 710, 650, and 470 nm observed in pure MgAl2O4 are related to the Mg vacancies and Mg–Al antisite defects. Interestingly, the intensities of these emission lines are enhanced by Zn doping. Unrestricted Hartree-Fock calculation for Zn-doped MgAl2O4 shows that in-gap impurity states are formed just above the valence-band maximum of MgAl2O4 when the Zn ion is substituted for the B-site Al ion. On the other hand, no in-gap state is formed when the Zn ion is substituted for the A-site Mg ion. The position of the Zn (3d) impurity level is identified by the photoemission measurement. The broad spectral features of the defect-induced states in pure MgAl2O4 is dramatically reduced by the Zn doping, indicating that holes supplied from the Zn ions at B site are trapped by the defect-induced states.
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78.40.Ha Other nonmetallic inorganics
79.60.-i Photoemission and photoelectron spectra
71.20.Ps Other inorganic compounds
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.55.Ht Other nonmetals
61.72.J- Point defects and defect clusters

Gain of a long-pulse KrCl excimer laser

L. C. Casper, H. M. J. Bastiaens, P. J. M. Peters, K.-J. Boller, and R. M. Hofstra

J. Appl. Phys. 102, 053110 (2007); http://dx.doi.org/10.1063/1.2772527 (6 pages) | Cited 2 times

Online Publication Date: 14 September 2007

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The net gain is measured for various pump power densities in a discharge-pumped long-pulse KrCl laser (222 nm). For this, a three-electrode laser system is employed, which is operated at high gas pressures of around 3.5 bar with pump power densities of 300−650 kW cm−3. The net gain reaches a maximum of 1.6% cm−1. Using the experimental results, values are calculated for the small-signal gain, the losses, and the saturation intensity. The losses and the saturation intensity are found to increase much stronger with the excitation rate than the small-signal gain. Fluorescence measurements at 222 nm show that the upper laser level depopulates faster when the power density increases. The influence of collisional quenching and the halogen consumption on the laser performance are discussed.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems

Ultrafast optical switching of three-dimensional Si inverse opal photonic band gap crystals

Tijmen G. Euser, Hong Wei, Jeroen Kalkman, Yoonho Jun, Albert Polman, David J. Norris, and Willem L. Vos

J. Appl. Phys. 102, 053111 (2007); http://dx.doi.org/10.1063/1.2777134 (6 pages) | Cited 12 times

Online Publication Date: 14 September 2007

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We present ultrafast optical switching experiments on three-dimensional photonic band gap crystals. Switching the Si inverse opal is achieved by optically exciting free carriers by a two-photon process. We probe reflectivity in the frequency range of second order Bragg diffraction where the photonic band gap is predicted. We find good experimental switching conditions for free-carrier plasma frequencies between 0.3 and 0.7 times the optical frequency ω: we thus observe a large frequency shift of up to Δω/ω = 1.5% of all spectral features including the peak that corresponds to the photonic band gap. We deduce a corresponding large refractive index change of ΔnSi′/nSi′ = 2.0%, where nSi′ is the refractive index of the silicon backbone of the crystal. The induced absorption length is longer than the sample thickness. We observe a fast decay time of 21 ps, which implies that switching could potentially be repeated at GHz rates. Such a high switching rate is relevant to future switching and modulation applications.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Possible colloid crystal formation in a magnetized and inhomogeneous semiconductor plasma

M. Salimullah, Z. Ehsan, K. Zubia, H. A. Shah, and G. Murtaza

J. Appl. Phys. 102, 053301 (2007); http://dx.doi.org/10.1063/1.2776153 (5 pages) | Cited 3 times

Online Publication Date: 5 September 2007

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We investigate the detailed properties of the modification of the Debye-Hückel and the consequent oscillatory wake potentials in the presence of a density inhomogeneity and external static uniform electric and magnetic fields in an ion-implanted n-type piezoelectric semiconductor. It is found that the external fields and the density nonuniformity have significant effects on the static and dynamical electrostatic potentials. The possibility of the long-ranged order formation of colloids of the implanted ions, leading to modification of the electrical, thermodynamic, and optical properties of the “soft matter,” has been pointed out. The periodic wakefields besides the usual static Coulombian Debye-Hückel potential may cause the long-range ordered structures of the charged colloidal particulates within the semiconductor to show various additional properties.
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52.27.Lw Dusty or complex plasmas; plasma crystals
77.65.-j Piezoelectricity and electromechanical effects
82.70.Dd Colloids

Ionic winds for locally enhanced cooling

David B. Go, Suresh V. Garimella, Timothy S. Fisher, and Rajiv K. Mongia

J. Appl. Phys. 102, 053302 (2007); http://dx.doi.org/10.1063/1.2776164 (8 pages) | Cited 19 times

Online Publication Date: 14 September 2007

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Ionic wind engines can be integrated onto surfaces to provide enhanced local cooling. Air ions generated by field-emitted electrons or a corona discharge are pulled by an electric field and exchange momentum with neutral air molecules, causing air flow. In the presence of a bulk flow, ionic winds distort the boundary layer, increasing heat transfer from the wall. Experiments demonstrate the ability of ionic winds to decrease the wall temperature substantially in the presence of a bulk flow over a flat plate, corresponding to local enhancement of the heat transfer coefficient by more than twofold. Multiphysics simulations of the corona and flow describe the ability of the ionic wind to distort a bulk flow boundary layer and confirm the experimentally observed heat transfer enhancement trends.
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52.77.-j Plasma applications
52.80.Hc Glow; corona
47.85.-g Applied fluid mechanics
47.15.Cb Laminar boundary layers
85.90.+h Other topics in electronic and magnetic devices and microelectronics (restricted to new topics in section 85)

Nitrogen dissociation degree in the diffusion region of a helicon plasma source obtained by atomic lines to molecular band intensities ratio

Costel Biloiu, Earl E. Scime, Ioana A. Biloiu, and Xuan Sun

J. Appl. Phys. 102, 053303 (2007); http://dx.doi.org/10.1063/1.2777998 (11 pages) | Cited 2 times

Online Publication Date: 14 September 2007

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Estimates of the dissociation degree in the diffusion region of a nitrogen helicon plasma source based on optical emission spectroscopy and Langmuir probe measurements are presented. The estimation procedure relies on measurements of the ratios of the intensities of the atomic triplet 3p 4S0→3s 4P (742.36, 744.23, and 746.83 nm) to the intensity of the 4-2 band of the first positive system (A 3Σu+→B 3Πg) at 750.39 nm and the measured relative vibrational distribution of the B 3Πg state. The electron energy distribution function, obtained from the second derivative of the Langmuir probe characteristic, and published excitation cross sections are used to calculate the electron-impact excitation rate coefficients—which are then compared to the atomic line and molecular band intensities to calculate the dissociation degree. For two distinct operating regimes, capacitively and inductively coupled, dissociation fractions of 5% and 13% are obtained in the expansion region of a 10 mTorr, 500 W, 10.74 MHz helicon generated nitrogen plasma. The dissociation degree results suggest that the helicon source can provide excited molecular species for plasma assisted molecular beam epitaxy of III-group nitrides.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.20.Fs Electron collisions
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.70.Ds Electric and magnetic measurements
52.50.Dg Plasma sources
52.80.Pi High-frequency and RF discharges

Comparative experimental analysis of the a-C:H deposition processes using CH4 and C2H2 as precursors

S. Peter, K. Graupner, D. Grambole, and F. Richter

J. Appl. Phys. 102, 053304 (2007); http://dx.doi.org/10.1063/1.2777643 (18 pages) | Cited 18 times

Online Publication Date: 14 September 2007

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The plasma enhanced chemical vapor deposition of a-C:H films using methane and acetylene as precursors was studied. Noninvasive in situ techniques were used to analyze the plasma processes with respect to the self-bias voltage, the displacement currents to the grounded electrode, the neutral gas composition, the optical sheath thickness as well as current and energy of the ions hitting the powered electrode. The a-C:H films were characterized for their deposition rate, surface roughness, hardness, mass density, and hydrogen content. Ion mean free paths, suitable for low-pressure rf sheaths, have been quantified for both precursors. The film with the highest hardness of 25 GPa was formed in the C2H2 discharge when the mean energy per deposited carbon atom was approximately 50 eV. The hardness obtained with the CH4 discharge was lower at 17 GPa and less sensitive to changes in the process parameters. It was found that the creation of hard (hardness >15 GPa) a-C:H films from both precursors is possible if the mean energy per deposited carbon atom exceeds only ∼ 15 eV. Further film characteristics such as surface roughness and hydrogen content show the interplay of ion flux and deposition from radicals to form the a-C:H structure and properties.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
68.60.Bs Mechanical and acoustical properties
52.77.Dq Plasma-based ion implantation and deposition
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.35.B- Structure of clean surfaces (and surface reconstruction)
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A transformation of carbon dioxide to nonmolecular solid at room temperature and high pressure

Tetsuji Kume, Yasuhisa Ohya, Masayuki Nagata, Shigeo Sasaki, and Hiroyasu Shimizu

J. Appl. Phys. 102, 053501 (2007); http://dx.doi.org/10.1063/1.2775539 (5 pages) | Cited 4 times

Online Publication Date: 4 September 2007

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Raman and infrared absorption spectra of solid carbon dioxide (CO2) have been measured at high pressures up to 80 GPa and room temperature. The broadening and weakening of lattice vibrational signals and the disappearance of molecular vibration were detected at 65 GPa by means of the Raman and infrared absorption experiments, respectively. The present Raman spectral feature is exactly the same as that of amorphous CO2 synthesized around 600 K and 60 GPa [ M. Santoro et al., Nature (London) 441, 857 (2006) ]. It is demonstrated that the polymerization of CO2 proceeds even at room temperature and almost independently of temperature.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
62.50.-p High-pressure effects in solids and liquids
78.35.+c Brillouin and Rayleigh scattering; other light scattering
82.35.Jk Copolymers, phase transitions, structure

Type IIA photosensitivity and formation of pores in optical fibers under intense ultraviolet irradiation

S. A. Kukushkin, M. G. Shlyagin, P. L. Swart, A. A. Chtcherbakov, and A. V. Osipov

J. Appl. Phys. 102, 053502 (2007); http://dx.doi.org/10.1063/1.2773996 (13 pages) | Cited 1 time

Online Publication Date: 4 September 2007

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Formation of the type IIA Bragg gratings in germanosilicate optical fibers is studied. We report the observation of such a type of gratings in the standard single-mode fiber (Corning SMF-28) under different experimental conditions. A mechanism for the type IIA photosensitivity in optical fibers is proposed which is based on nucleation and evolution of pores from vacancy-type defects in fiber areas where a high level of mechanical stress is induced under intense ultraviolet (UV) light. Evolution of fiber core temperature under influence of a single 20 ns light pulse from a KrF excimer laser was measured and compared with theoretical calculations. It was shown that transient thermoinduced stress in the fiber core can achieve a level sufficient for effective nucleation of pores. A theory describing formation of pores in optical fibers has been developed and was used to estimate the pore nucleation rate, concentration, and other parameters of pore evolution for different levels of UV fluence and fiber core stress.
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42.81.Cn Fiber testing and measurement of fiber parameters
42.70.Ce Glasses, quartz
61.43.Fs Glasses
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Equation of motion of a phonon gas and non-Fourier heat conduction

Bing-Yang Cao and Zeng-Yuan Guo

J. Appl. Phys. 102, 053503 (2007); http://dx.doi.org/10.1063/1.2775215 (6 pages) | Cited 19 times

Online Publication Date: 4 September 2007

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Heat conduction in solids is due to the motion of the phonon gas. A more general description of the heat transport in solids includes consideration of the mass, pressure, and inertial force of the phonon gas. The mass of the phonon gas refers to the equivalent mass of its energy based on Einstein’s mass-energy relation. The thermal vibration of the lattice creates the phonon gas pressure and the momentum change of the phonon gas results in an inertial force. The phonon gas velocity is directly proportional to the heat flux. These concepts are used to establish an equation of motion for the phonon gas including the driving, inertial, and resistant forces using Newtonian dynamics. This equation reduces to Fourier’s law of heat conduction when the inertial force can be neglected relative to the other terms so that heat conduction becomes pure diffusion. However, Fourier’s law of heat conduction no longer holds if the heat flux is very high, such that the inertial force of the phonon gas is not negligible. In such cases, the heat conduction behavior deviates from Fourier’s law even for steady-state conditions so that the heat conduction is characterized by a nonlinear relationship between the heat flux and the temperature gradient.
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44.10.+i Heat conduction
63.10.+a General theory

Reducing the critical thickness of epitaxial Ag film on the Si(111) substrate by introducing a monolayer Al buffer layer

Zhe Tang, Jing Teng, Ying Jiang, JinFeng Jia, Jiandong Guo, and Kehui Wu

J. Appl. Phys. 102, 053504 (2007); http://dx.doi.org/10.1063/1.2773630 (4 pages)

Online Publication Date: 5 September 2007

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We report a method to prepare atomically smooth Ag film, with thickness as small as 2 monolayers (ML) and a well-defined interface on the Si(111) substrate, by introducing a monolayer Al(111) 1×1 buffer layer. Scanning tunneling microscopy, low-energy electron diffraction, and x-ray photoelectron emission diffraction were employed to in situ study the film and interface structures. Compared with the growth of Ag on a clean Si(111) 7×7 surface, the buffer layer lowers the critical thickness from 6 to 2 ML. The effect is explained based on an enhanced charge spillage at the interface.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness
79.60.Bm Clean metal, semiconductor, and insulator surfaces

A model for electromigration-induced degradation mechanisms in dual-inlaid copper interconnects: Effect of microstructure

Valeriy Sukharev, Ehrenfried Zschech, and William D. Nix

J. Appl. Phys. 102, 053505 (2007); http://dx.doi.org/10.1063/1.2775538 (14 pages) | Cited 13 times

Online Publication Date: 5 September 2007

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A developed physical model and a simulation algorithm are used to predict electromigration (EM)-induced stress evolution in dual-inlaid copper interconnects. Incorporation of all important atom migration driving forces into the mass balance equation and its solution, together with the solution of the coupled electromagnetics and elasticity problems, allows the simulation of EM-induced degradation in a variety of dual-inlaid copper interconnect segments with different dominant paths for mass transport [ V. Sukharev and E. Zschech, J. Appl. Phys. 96, 6337 (2004) ]. The results of the numerical simulation have been proven experimentally by EM degradation studies on fully embedded dual-inlaid copper interconnect test structures and by subsequent microstructure analysis, mainly based on electron backscatter diffraction (EBSD) data. The EM-induced void formation and its virtual movement and growth in a copper interconnect were continuously monitored in an in situ scanning electron microscopy experiment. The copper microstructure, particularly the orientation of grains and grain boundaries, was determined with EBSD. It has a significant influence on grain boundary diffusivity and consequently on the mass transport along grain boundaries. For interconnects with interfaces that resist atomic transport and where grain boundaries are the important pathways for atom migration [ E. Zschech et al., Z. Metallkd. 96, 996 (2005) ], degradation and failure processes are completely different for microstructures with randomly oriented grain boundaries compared with “bamboolike” microstructures. The correspondence between simulation results and experimental data indicates the applicability of the developed model for optimization of the physical and electrical design rules. Simulation-based optimization of the interconnect architecture, segment geometry, material properties, and some of the process parameters can produce on-chip interconnect systems with a high immunity to EM-induced failures.
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85.40.Ls Metallization, contacts, interconnects; device isolation
81.05.Bx Metals, semimetals, and alloys
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
66.30.Qa Electromigration
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Epitaxial lateral overgrowth of a-plane GaN by metalorganic chemical vapor deposition

X. Ni, Ü. Özgür, H. Morkoç, Z. Liliental-Weber, and H. O. Everitt

J. Appl. Phys. 102, 053506 (2007); http://dx.doi.org/10.1063/1.2773692 (7 pages) | Cited 13 times

Online Publication Date: 6 September 2007

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We report on epitaxial lateral overgrowth (ELO) of (11math0) a-plane GaN by metalorganic chemical vapor deposition. Different growth rates of Ga- and N-polar wings together with wing tilt create a major obstacle for achieving a smooth, fully coalesced surface in ELO a-plane GaN. To address this issue a two-step growth method was employed to provide a large aspect ratio of height to width in the first growth step followed by enhanced lateral growth in the second by controlling the growth temperature. By this method, the average ratio of Ga- to N-polar wing growth rate has been reduced from 4–6 to 1.5–2, which consequently reduced the wing-tilt induced height difference between the two approaching wings at the coalescence front, thereby making their coalescence much easier. Transmission electron microscopy showed that the threading dislocation density in the wing regions was 1.0×108 cm−2, more than two orders of magnitude lower than that in the window regions (4.2×1010 cm−2). However, a relatively high density of basal stacking faults of 1.2×104 cm−1 was still present in the wing regions as compared to c -plane GaN, where they are rarely observed away from the substrate. Atomic force microscopy (AFM) measurements showed two orders of magnitude higher density of surface pits in the window than in the wing regions, which were considered to be terminated by dislocations (partial ones related to stacking faults and full ones) on the surface. The existence of basal stacking faults was also revealed by AFM measurements on the a-plane ELO sample after wet chemical etching in hot H3PO4/H2SO4 (1:1). The extensions of Ga-polar wings near the meeting fronts were almost free of stacking faults. The improvement of crystalline quality in the overgrown layer by ELO was also verified by near field scanning optical microscopy and time-resolved photoluminescence measurements; the former showing strongly enhanced luminescence from the wing regions, and the latter indicating longer decay times (0.25 ns) compared to a standard a-plane GaN template (40 ps).
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
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.)
61.72.Nn Stacking faults and other planar or extended defects

Synchrotron x-ray microscopy studies on electromigration of a two-phase material

A. Lee, W. Liu, C. E. Ho, and K. N. Subramanian

J. Appl. Phys. 102, 053507 (2007); http://dx.doi.org/10.1063/1.2777122 (5 pages) | Cited 9 times

Online Publication Date: 6 September 2007

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Basic issues involving movement of conductive constituents and microstructural evolution from high current density in single phase materials are well documented. Recently, electromigration of conductive constituents in multiphase materials has gained attention due to the necessity of employing such alloys for interconnects in microelectronics. Reported studies on these alloys using complicated industrial geometry suffer from contributions such as current crowding. Hence a basic understanding on operative mechanisms during electromigration in multiphase alloys cannot be gained from these studies. Consequently, several mechanisms proposed from these studies involve fitting parameters and not well-understood complex diffusional processes. A joint configuration designed to avoid current crowding and associated local Joule heating is suitable for evaluating electromigration induced microstructural events. Synchrotron x-ray microscopy has provided information regarding two- and three-dimensional crystallographic orientations and strain fields in such joints, aiding the development of a basic understanding of electromigration in two-phase alloys.
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66.30.Qa Electromigration
68.37.Yz X-ray microscopy
85.40.Ls Metallization, contacts, interconnects; device isolation

Surface acoustic wave depth profiling of a functionally graded material

Jozefien Goossens, Philippe Leclaire, Xiaodong Xu, Christ Glorieux, Loic Martinez, Antonella Sola, Cristina Siligardi, Valeria Cannillo, Tom Van der Donck, and Jean-Pierre Celis

J. Appl. Phys. 102, 053508 (2007); http://dx.doi.org/10.1063/1.2774002 (8 pages) | Cited 2 times

Online Publication Date: 7 September 2007

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The potential and limitations of Rayleigh wave spectroscopy to characterize the elastic depth profile of heterogeneous functional gradient materials are investigated by comparing simulations of the surface acoustic wave dispersion curves of different profile-spectrum pairs. This inverse problem is shown to be quite ill posed. The method is then applied to extract information on the depth structure of a glass-ceramic (alumina) functionally graded material from experimental data. The surface acoustic wave analysis suggests the presence of a uniform coating region consisting of a mixture of Al2O3 and glass, with a sharp transition between the coating and the substrate. This is confirmed by scanning electron microscope with energy dispersive x-ray analysis.
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68.35.Iv Acoustical properties
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

High pressure photoluminescence of CdZnSe quantum dots: Alloying effect

Zhi Zhao, Jie Zeng, Zejun Ding, Xiaoping Wang, Jianguo Hou, and Zengming Zhang

J. Appl. Phys. 102, 053509 (2007); http://dx.doi.org/10.1063/1.2777135 (3 pages) | Cited 7 times

Online Publication Date: 10 September 2007

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The pressure dependence of photoluminescence of wurtzite 5.5 nm CdZnSe alloy quantum dots (QDs) was studied and compared with that of the wurtzite 3.5 nm CdSe QDs. The direct Γ energy gaps of wurtzite QDs were found to increase with the pressure, and the pressure coefficients were gained as 35.4 meV/GPa for CdZnSe and 28.4 meV/GPa for CdSe QDs. The authors attributed the high value of pressure coefficient for CdZnSe alloy QDs to the alloying effect with strengthening the anion-cation s‐s orbital coupling and weakening p‐d orbital coupling in the alloy. The result demonstrates that the alloying process has a dominant role in the electronic state and structure transition under high pressure.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
62.50.-p High-pressure effects in solids and liquids
68.65.Hb Quantum dots (patterned in quantum wells)
64.70.K- Solid-solid transitions
73.21.La Quantum dots

An adhesion model for elastic-plastic fractal surfaces

Y. F. Peng and Y. B. Guo

J. Appl. Phys. 102, 053510 (2007); http://dx.doi.org/10.1063/1.2777476 (7 pages) | Cited 3 times

Online Publication Date: 11 September 2007

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The strong adherence (stiction) of adjacent surfaces is a major design concern in microelectromechanical system. The present research concerns the elastic-plastic adhesion of a rough surface contacting with a rigid flat. Rough surface is characterized by fractal geometry using a two-variable Weierstrass-Mandelbrot function [ The Fractal Geometry of Nature (Freeman, New York, 1982) ]. The microcontact model of single asperity is established in terms of fractal parameters, and the plastic adhesion model is also developed with the Dugdale approximation to consider the adhesive interaction within and outside the contact area. Then according to the plastic flow criterion, the Maguis-Dugdale transition theory [ Adhesion of Adhesion and Rapture of Elastic Solids (Springer-Verlag, New York, 2005) ] and the plastic adhesion model are used to solve the elastic-plastic adhesive interaction for the two approaching surfaces by incorporating the fractal surface model. Simulations of the adherence force versus the approaching distance of surfaces are performed. The necessity of considering the plastic deformation in microsized interface adhesion is also validated by comparing the result of the presented model with that of the Morrow model [ J. Tribol 127, 206 (2005) ]. The influence of fractal parameters on adherence force shows that controlling the surface topography is a readily means to control the adherence force for the elastic-plastic adhesion of rough surfaces, which is due to the intermolecular adhesive interactions.
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46.55.+d Tribology and mechanical contacts
46.35.+z Viscoelasticity, plasticity, viscoplasticity
46.25.Cc Theoretical studies
68.35.Np Adhesion
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