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15 Mar 2005

Volume 97, Issue 6, Articles (06xxxx)

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Luminescence properties of defects in GaN

Michael A. Reshchikov and Hadis Morkoç

J. Appl. Phys. 97, 061301 (2005); http://dx.doi.org/10.1063/1.1868059 (95 pages) | Cited 298 times

Online Publication Date: 15 March 2005

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Gallium nitride (GaN) and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet (UV) emitters and detectors (in photon ranges inaccessible by other semiconductors) and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these nitride semiconductors. Even though GaN broke the long-standing paradigm that high density of dislocations precludes acceptable device performance, point defects have taken the center stage as they exacerbate efforts to increase the efficiency of emitters, increase laser operation lifetime, and lead to anomalies in electronic devices. The point defects include native isolated defects (vacancies, interstitial, and antisites), intentional or unintentional impurities, as well as complexes involving different combinations of the isolated defects. Further improvements in device performance and longevity hinge on an in-depth understanding of point defects and their reduction. In this review a comprehensive and critical analysis of point defects in GaN, particularly their manifestation in luminescence, is presented. In addition to a comprehensive analysis of native point defects, the signatures of intentionally and unintentionally introduced impurities are addressed. The review discusses in detail the characteristics and the origin of the major luminescence bands including the ultraviolet, blue, green, yellow, and red bands in undoped GaN. The effects of important group-II impurities, such as Zn and Mg on the photoluminescence of GaN, are treated in detail. Similarly, but to a lesser extent, the effects of other impurities, such as C, Si, H, O, Be, Mn, Cd, etc., on the luminescence properties of GaN are also reviewed. Further, atypical luminescence lines which are tentatively attributed to the surface and structural defects are discussed. The effect of surfaces and surface preparation, particularly wet and dry etching, exposure to UV light in vacuum or controlled gas ambient, annealing, and ion implantation on the characteristics of the defect-related emissions is described.
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81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
81.40.Tv Optical and dielectric properties related to treatment conditions
61.72.J- Point defects and defect clusters
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.S- Impurities in crystals
81.65.Cf Surface cleaning, etching, patterning
61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
71.55.Eq III-V semiconductors
61.82.Fk Semiconductors
81.40.Wx Radiation treatment (particle and electromagnetic)
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Fabrication and evaluation of GaN negative and bifocal microlenses

H. W. Choi, E. Gu, C. Liu, J. M. Girkin, and M. D. Dawson

J. Appl. Phys. 97, 063101 (2005); http://dx.doi.org/10.1063/1.1857062 (3 pages) | Cited 6 times

Online Publication Date: 11 March 2005

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Methods of fabricating negative and bifocal microlens arrays have been demonstrated in this paper. The technique of photoresist molding using a sapphire positive lens template was used for the patterning of negative microlenses, while the bifocal microlens arrays were fabricated using a two-step etch process. In both cases, the lenses were etched using inductively coupled plasma. Microlenses with diameters as small as 10 μm have been demonstrated and were characterized using atomic force microscopy and confocal microscopy. The lens arrays were found to be smooth, uniform, and to have focal lengths consistent with their design and calculated values.
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42.79.Bh Lenses, prisms and mirrors
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays
52.77.Bn Etching and cleaning
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning
68.37.Ps Atomic force microscopy (AFM)

Laser-induced refractive index gratings formed in Pr3+-doped sodium-magnesium-aluminosilicate glasses

Abdulatif Y. Hamad and James P. Wicksted

J. Appl. Phys. 97, 063102 (2005); http://dx.doi.org/10.1063/1.1861971 (8 pages)

Online Publication Date: 11 March 2005

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We report a systematic study of grating formation in which the Pr2O3 concentration [Pr2O3] in sodium-magnesium-aluminosilicate glasses is varied from 0.5 to 5 mol %. The grating kinetics is reported as functions of the [Pr2O3] and the write-beam irradiance. The maximum persistent change in the index of refraction was 1×10−5. The persistent change in the index of refraction initially decreased linearly as a function of the [Pr2O3] and showed a limiting behavior at the highest [Pr2O3]. No appreciable transient change in the index of refraction, Δntran, was measured. This was attributed to the low probability of the multiphonon relaxation of the math level of the Pr3+ ions as determined through fluorescence measurements. The results of this study are consistent with a recently developed small modifier diffusion model.
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42.70.Ce Glasses, quartz
42.79.Dj Gratings
42.62.-b Laser applications

Quantitative characterization of inertial confinement fusion capsules using phase contrast enhanced x-ray imaging

B. J. Kozioziemski, J. A. Koch, A. Barty, H. E. Martz, Wah-Keat Lee, and Kamel Fezzaa

J. Appl. Phys. 97, 063103 (2005); http://dx.doi.org/10.1063/1.1862764 (9 pages) | Cited 15 times

Online Publication Date: 14 March 2005

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Current designs for inertial confinement fusion capsules for the National Ignition Facility consist of a solid deuterium–tritium (D–T) fuel layer inside of a copper doped beryllium, Be(Cu), shell. Phase contrast enhanced x-ray imaging is shown to render the D–T layer visible inside the Be(Cu) shell. Phase contrast imaging is experimentally demonstrated for several surrogate capsules and validates computational models. Polyimide and low density divinyl benzene foam shells were imaged at the Advanced Photon Source synchrotron. The surrogates demonstrate that phase contrast enhanced imaging provides a method to characterize surfaces when absorption imaging cannot be used. Our computational models demonstrate that a rough surface can be accurately characterized using phase contrast enhanced x-ray images.
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07.85.-m X- and γ-ray instruments
68.35.Ct Interface structure and roughness
28.52.Fa Materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
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Radio frequency sheath formation and excitation around a stepped electrode

E. V. Barnat and G. A. Hebner

J. Appl. Phys. 97, 063301 (2005); http://dx.doi.org/10.1063/1.1846939 (6 pages) | Cited 9 times

Online Publication Date: 1 March 2005

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Plasma and sheath structure around a rf excited stepped electrode is investigated. Laser-induced fluorescence dip spectroscopy is used to spatially resolve sheath fields in an argon discharge while optical emission and laser-induced fluorescence are used to measure the spatial structure of the surrounding discharge for various discharge conditions and step-junction configurations. The presence of the step perturbs the spatial structure of the fields around the step as well as the excitation in the region above the step.
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52.40.Kh Plasma sheaths
52.80.Pi High-frequency and RF discharges
52.25.Jm Ionization of plasmas
52.38.-r Laser-plasma interactions

Low-impedance internal linear inductive antenna for large-area flat panel display plasma processing

K. N. Kim, S. J. Jung, Y. J. Lee, G. Y. Yeom, S. H. Lee, and J. K. Lee

J. Appl. Phys. 97, 063302 (2005); http://dx.doi.org/10.1063/1.1861136 (4 pages) | Cited 6 times

Online Publication Date: 4 March 2005

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An internal-type linear inductive antenna, that is, a double-comb-type antenna, was developed for a large-area plasma source having the size of 1020 mm×830 mm, and high density plasmas on the order of 2.3×1011 cm−3 were obtained with 15 mTorr Ar at 5000 W of inductive power with good plasma stability. This is higher than that for the conventional serpentine-type antenna, possibly due to the low impedance, resulting in high efficiency of power transfer for the double-comb antenna type. In addition, due to the remarkable reduction of the antenna length, a plasma uniformity of less than 8% was obtained within the substrate area of 880 mm×660 mm at 5000 W without having a standing-wave effect.
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52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.77.-j Plasma applications
52.50.Dg Plasma sources
42.79.Kr Display devices, liquid-crystal devices
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.-b Plasma properties

Influence of stoichiometry of direct plasma-enhanced chemical vapor deposited SiNx films and silicon substrate surface roughness on surface passivation

Stefaan De Wolf, Guido Agostinelli, Guy Beaucarne, and Petko Vitanov

J. Appl. Phys. 97, 063303 (2005); http://dx.doi.org/10.1063/1.1861138 (8 pages) | Cited 24 times

Online Publication Date: 4 March 2005

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In this article, we report on the use of direct plasma-enhanced chemical vapor deposited silicon nitride (SiNx) films deposited at low excitation frequency (440 kHz) on low-resistivity (1.5 Ω cm) p-type Czochralski silicon substrate surfaces with different textures, to elucidate the influence of microroughness of the substrate surface on the surface-passivating properties of thin SiNx films. Whereas flat surfaces get the best passivation from Si-rich SiNx films, the optimum passivation shifts towards stoichiometric nitride as the microroughness increases, which points to the increasing relative importance of a charge-induced field effect. When short high-temperature (firing) treatments are applied upon passivation layer deposition, the process window to yield good surface passivation broadens, although very Si-rich films tend to suffer from blistering.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.65.Rv Passivation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.55.-g Dielectric thin films
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.Nq Composition and phase identification
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
73.20.At Surface states, band structure, electron density of states

Calculation of the electrode shape for suppression of the standing wave effect in large area rectangular capacitively coupled reactors

L. Sansonnens

J. Appl. Phys. 97, 063304 (2005); http://dx.doi.org/10.1063/1.1862770 (6 pages) | Cited 8 times

Online Publication Date: 9 March 2005

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The electromagnetic standing wave becomes one of the main sources of plasma nonuniformity in large area capacitively coupled rf reactors. In cylindrical reactors with a central rf connection or one-dimensional linear reactors with rf connections at both extremities, Gaussian shaped electrodes can be used to suppress this standing wave. In this work, we present a two-dimensional quasiplanar circuit model and a numerical method for calculation of the electrode shape that can suppress the standing wave effect in large area rectangular reactors. It is shown that the calculated shapes are not Gaussian, and are not only a function of the reactor dimensions and excitation frequency, but are also strongly influenced by the position and number of rf connections, as will also be the case for a cylindrical reactor with a noncentral rf connection. However, when a shape has been determined for a given reactor geometry and rf excitation frequency, then it is shown that it remains independent of the plasma provided that the electromagnetic skin depth in the plasma remains large enough such that skin effects remain negligible.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.58.Qv Electrostatic and high-frequency confinement
52.40.Kh Plasma sheaths

Laser ablation of Cu and plume expansion into 1 atm ambient gas

Zhaoyang Chen and Annemie Bogaerts

J. Appl. Phys. 97, 063305 (2005); http://dx.doi.org/10.1063/1.1863419 (12 pages) | Cited 42 times

Online Publication Date: 14 March 2005

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A one-dimensional gas-dynamic model is presented for the laser ablation of Cu and the expansion of the Cu vapor in a background gas (He) at 1 atm. The ionization of Cu and He, the inverse bremsstrahlung absorption processes and photoionization process, and the back flux onto the target are considered simultaneously. The binary diffusion, the viscosity, and the thermal conduction including the electron thermal conduction are considered as well. Numerical results show that the consideration of ionization and laser absorption in the plume greatly influences the gas dynamics. The ionization of Cu enables the recondensation at the target surface to happen even during the laser pulse. The ionization degree of Cu and He may change greatly with the location in the plume. For laser irradiances ranging from 2 to 9×1012 W/m2, the simulations show that the second-order ionization of Cu competes with the first-order ionization. In the region close to the target surface, the first-order ionization of Cu dominates. In the core of the plasma, the second-order ionization of Cu may dominate over the first-order ionization at laser irradiances higher than 7×1012 W/m2. In the mixing layer, the first-order ionization of Cu is always more important than the second-order ionization although the latter increases monotonously with laser irradiance. The ionization of He is only important in the mixing layer. The plume expansion velocity is much larger than that without ionization and laser absorption by the plume. The relative importance of different laser absorption mechanisms may change with time. Close to the surface photoionization and electron-neutral inverse bremsstrahlung are always important. Once the ionization in the plume starts, at later time, electron-ion inverse bremsstrahlung can become more important than photoionization in the plume core until the shock wave front. Unlike in the vacuum case, electron-neutral inverse bremsstrahlung is very strong due to the relatively high number density of neutral atoms in the plume in the presence of a dense ambient gas. A similar laser irradiance threshold is found for the ablation rate and the plasma formation in the plume, which agrees well with the case of nanosecond laser ablation of metals in vacuum.
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52.65.-y Plasma simulation
52.38.Mf Laser ablation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Fi Transport properties
52.25.Jm Ionization of plasmas
52.25.Kn Thermodynamics of plasmas
52.25.Tx Emission, absorption, and scattering of particles
52.35.Tc Shock waves and discontinuities

Plasma analyses during femtosecond laser ablation of Ti, Zr, and Hf

D. Grojo, J. Hermann, and A. Perrone

J. Appl. Phys. 97, 063306 (2005); http://dx.doi.org/10.1063/1.1861519 (9 pages) | Cited 27 times

Online Publication Date: 15 March 2005

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Femtosecond laser ablation of Ti, Zr, and Hf has been investigated by means of in situ plasma diagnostics. Fast imaging was used to characterize the plasma plume expansion on a nanosecond time scale. In addition, time- and space-resolved optical emission spectroscopy was employed to determine the plume composition and the characteristic expansion velocities of plasma species. It is shown that two plume components with different expansion velocities are generated by the interaction of ultrashort laser pulses with metals. The composition and the expansion behavior of the two components have been analyzed as a function of laser fluence and target material. The results are discussed in terms of mechanisms responsible for ablation by ultrashort laser pulses.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.38.Mf Laser ablation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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Tuning of cross-linking and mechanical properties of laser-deposited poly (methyl methacrylate) films

Erik Süske, Thorsten Scharf, Hans-Ulrich Krebs, Elena Panchenko, Thomas Junkers, Mark Egorov, Michael Buback, and Harald Kijewski

J. Appl. Phys. 97, 063501 (2005); http://dx.doi.org/10.1063/1.1850609 (4 pages) | Cited 12 times

Online Publication Date: 1 March 2005

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The chemical composition, amount of cross-linking and its influence on the mechanical properties of poly(methyl methacrylate) (PMMA) thin films produced by pulsed laser deposition (PLD) at a wavelength of 248 nm under ultrahigh vacuum were investigated by infrared spectroscopy, scanning electron microscopy, size-exclusion chromatography, thermogravimetric analysis, and nanoindentation experiments. The films consist of two components, one fraction with a molecular weight well below that of the target material and a second fraction, which is cross-linked. Compared to bulk material, the Young’s modulus of the film is increased. The amount of cross-linking in the film can be tuned by the applied laser fluence leading to changes of the mechanical properties.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.60.Bs Mechanical and acoustical properties
68.55.Nq Composition and phase identification
61.82.Pv Polymers, organic compounds
68.55.-a Thin film structure and morphology
61.41.+e Polymers, elastomers, and plastics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
78.66.Qn Polymers; organic compounds
68.35.Gy Mechanical properties; surface strains
78.30.Jw Organic compounds, polymers
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
82.80.Bg Chromatography
62.20.Qp Friction, tribology, and hardness
62.20.D- Elasticity

Optical and morphological study of disorder in opals

E. Palacios-Lidón, B. H. Juárez, E. Castillo-Martínez, and C. López

J. Appl. Phys. 97, 063502 (2005); http://dx.doi.org/10.1063/1.1851014 (7 pages) | Cited 16 times

Online Publication Date: 1 March 2005

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An optical and morphological study has been carried out to understand the role of intrinsic defects in the optical properties of opal-based photonic crystals. By doping poly(methylmethacrylate) (PMMA) thin-film opals with larger polystyrene (PS) spheres, structural disorder has being generated perturbing the PMMA matrix periodicity. It is shown that this disorder dramatically affects the optical response of the system worsening its photonic properties. It has been found that the effect of doping is highly dependent not only on the concentration but also on the relative size of the dopant with reference to the matrix. Through a detailed scanning electron microscopy inspection, the sort of structural defects involved, derived from the different particle size used, has been characterized. A direct relationship between the observed optical response with the different perturbations generated in the lattice has been found. In addition, from this study it can be concluded that it is possible to grow high quality alloyed photonic crystals, exhibiting intermediate photonic properties between pure PMMA and pure PS opals by simple sphere size matching and variation of the relative concentration of both components.
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42.70.Qs Photonic bandgap materials
78.66.Qn Polymers; organic compounds
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.J- Point defects and defect clusters
61.72.S- Impurities in crystals
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Analysis of copper-rich precipitates in silicon: Chemical state, gettering, and impact on multicrystalline silicon solar cell material

Tonio Buonassisi, Matthew A. Marcus, Andrei A. Istratov, Matthias Heuer, Theodore F. Ciszek, Barry Lai, Zhonghou Cai, and Eicke R. Weber

J. Appl. Phys. 97, 063503 (2005); http://dx.doi.org/10.1063/1.1827913 (9 pages) | Cited 17 times

Online Publication Date: 1 March 2005

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In this study, synchrotron-based x-ray absorption microspectroscopy (μ-XAS) is applied to identify the chemical states of copper-rich clusters within a variety of silicon materials, including as-grown cast multicrystalline silicon solar cell material with high oxygen concentration and other silicon materials with varying degrees of oxygen concentration and copper contamination pathways. In all samples, copper silicide (Cu3Si) is the only phase of copper identified. It is noted from thermodynamic considerations that unlike certain metal species, copper tends to form a silicide and not an oxidized compound because of the strong silicon–oxygen bonding energy; consequently the likelihood of encountering an oxidized copper particle in silicon is small, in agreement with experimental data. In light of these results, the effectiveness of aluminum gettering for the removal of copper from bulk silicon is quantified via x-ray fluorescence microscopy, and a segregation coefficient is determined from experimental data to be at least (1–2)×103. Additionally, μ-XAS data directly demonstrate that the segregation mechanism of Cu in Al is the higher solubility of Cu in the liquid phase. In light of these results, possible limitations for the complete removal of Cu from bulk mc-Si are discussed.
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64.75.-g Phase equilibria
61.72.S- Impurities in crystals
61.72.Yx Interaction between different crystal defects; gettering effect
65.40.G- Other thermodynamical quantities
78.70.Dm X-ray absorption spectra

Bounds and estimates for transport coefficients of random and porous media with high contrasts

James G. Berryman

J. Appl. Phys. 97, 063504 (2005); http://dx.doi.org/10.1063/1.1854732 (11 pages) | Cited 10 times

Online Publication Date: 1 March 2005

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Bounds on transport coefficients of random polycrystals of laminates are presented, including the well-known Hashin–Shtrikman bounds and some rigorous bounds involving two formation factors for a two-component porous medium. A class of self-consistent estimators is then formulated based on the observed analytical structure both of these bounds and also of earlier self-consistent estimates [of the coherent potential approximation (CPA) or CPA-type]. A numerical study is made, assuming first that the internal structure (i.e., the laminated grain structure) is not known, and then that it is known. The purpose of this aspect of the study is to attempt to quantify the differences in the predictions of properties of a system being modeled when such organized internal structure is present in the medium but detailed spatial correlation information may or (more commonly) may not be available. Some methods of estimating formation factors from data are also presented and then applied to a high-contrast fluid-permeability numerical simulation data set. Hashin–Shtrikman bounds are found to be very accurate estimates for low contrast heterogeneous media. But formation factor lower bounds are superior estimates for high contrast situations. Other related bounds by Bergman that interpolate between the Hashin–Shitrikman bounds and the formation factor bounds are also briefly discussed. The self-consistent estimators developed here also tend to agree better with data than either the bounds or the CPA estimates, which themselves tend to overestimate values for high-contrast conducting composites.
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72.10.Bg General formulation of transport theory
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.43.Gt Powders, porous materials

Importance of the gas phase role to the prediction of energetic material behavior: An experimental study

A. N. Ali, S. F. Son, B. W. Asay, and R. K. Sander

J. Appl. Phys. 97, 063505 (2005); http://dx.doi.org/10.1063/1.1863428 (7 pages) | Cited 7 times

Online Publication Date: 1 March 2005

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Various thermal (radiative, conductive, and convective) initiation experiments are performed to demonstrate the importance of the gas phase role in combustion modeling of energetic materials (EM). A previously published condensed phase model that includes a predicted critical irradiance above which ignition is not possible is compared to experimental laser ignition results for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 2,4,6-trinitrotoluene (TNT). Experimental results conflict with the predicted critical irradiance concept. The failure of the model is believed to result from a misconception about the role of the gas phase in the ignition process of energetic materials. The model assumes that ignition occurs at the surface and that evolution of gases inhibits ignition. High speed video of laser ignition, oven cook-off and hot wire ignition experiments captures the ignition of HMX and TNT in the gas phase. A laser ignition gap test is performed to further evaluate the effect of gas phase laser absorption and gas phase disruption on the ignition process. Results indicate that gas phase absorption of the laser energy is probably not the primary factor governing the gas phase ignition observations. It is discovered that a critical gap between an HMX pellet and a salt window of 6 mm±0.4 mm exists below which ignition by CO2 laser is not possible at the tested irradiances of 29 W/cm2 and 38 W/cm2 for HMX ignition. These observations demonstrate that a significant disruption of the gas phase, in certain scenarios, will inhibit ignition, independent of any condensed phase processes. These results underscore the importance of gas phase processes and illustrate that conditions can exist where simple condensed phase models are inadequate to accurately predict the behavior of energetic materials.
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82.33.Vx Reactions in flames, combustion, and explosions
82.60.Cx Enthalpies of combustion, reaction, and formation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.62.-b Laser applications
61.82.Pv Polymers, organic compounds

High coupling KNbO3 width-extensional vibrators with a polar multidomain structure

Hirokatsu Koyama, Kiyoshi Nakamura, and Takehiro Takano

J. Appl. Phys. 97, 063506 (2005); http://dx.doi.org/10.1063/1.1861986 (4 pages)

Online Publication Date: 4 March 2005

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The longitudinal piezoelectric coupling factor for the width-extensional mode of a thin KNbO3 plate, k11′, has theoretically been predicted to be as high as 82.4% for the 43.5° rotated Z cut about the Y axis. To experimentally confirm the predicted value we fabricated a width-extensional vibrator using a 45° rotated Z cut plate about the Y axis, which is close to the maximum k11′ cut. However, the measured value of k11′ was 71.3%, appreciably lower than the predicted value. It is clarified that the lower coupling factor can be ascribed to the tilt of the electric-field vector from the major face of the plate, which results from an off-diagonal component of the dielectric tensor. To prevent the electric-field tilt, a polar multidomain structure consisting of two kinds of 90° domains is introduced into the width-extensional vibrator instead of a single-domain structure. It is demonstrated by finite element method simulations that the coupling factor approaches the predicted value (82.4%) as the number of domains formed in the vibrator increases. The measured coupling factor of a width-extensional vibrator with a polar multidomain structure is as high as 79.4%, which is close to the predicted value. An additional advantage of using this domain structure is its lower spurious response.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.80.Dj Domain structure; hysteresis
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
43.38.-p

Limitations of the stretched exponential function for describing dynamics in disordered solid materials

D. Apitz and P. M. Johansen

J. Appl. Phys. 97, 063507 (2005); http://dx.doi.org/10.1063/1.1852069 (4 pages) | Cited 6 times

Online Publication Date: 4 March 2005

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Around the glass transition temperature, relaxation dynamics in glass-forming materials follows a strong nonexponential behavior. It is widely accepted that an empirically based stretched exponential function, known as the Kohlrausch–Williams–Watts (KWW) function, ϕ(t) = e−(t/τ)β, describes universally a broad variety of experimental data. Using intuitive pictures and ellipsometric measurements, we show that (1) in order to describe the dynamics in disordered materials such as in polymers using a KWW function, the response has to be considered over a specific region of time, (2) a single KWW function is not sufficient for correctly describing more than one relaxation processes, and (3) in certain cases, stretching exponents depending on temperature do not cover the ranges previously suggested (from 0 to 1, e.g., as a sigmoid function). As an example, we show that the temperature dependence of the stretching exponent β(T) depends highly on how the curve fits with the KWW function are performed.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
64.60.Cn Order-disorder transformations

Elimination of defect-induced color instabilities in polymer light-emitting devices

G. Mauthner, M. Collon, E. J. W. List, F. P. Wenzl, M. Bouguettaya, and J. R. Reynolds

J. Appl. Phys. 97, 063508 (2005); http://dx.doi.org/10.1063/1.1850172 (5 pages) | Cited 8 times

Online Publication Date: 7 March 2005

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We demonstrate that utilizing a blue light-emitting oligo(ethylene oxide)-grafted conjugated poly(p-phenylene) (PPP-OR11) as an active layer in a light-emitting electrochemical cell (LEC) preserves a color-stable blue light emission. This is in contrast to the polymer light-emitting diodes (PLEDs) constructed using the same emitting polymer without ionic species, which exhibits a rapid red shifting of the emission to a distinct green. We attribute the color shift to various degradation processes caused by oxidative degradation and aluminum deposition-induced defects in PPP-OR11. The analysis of the degradation processes in the PLEDs shows that the color stability in the LEC is caused by a controlled shift of the recombination zone from the defects including cathode∕polymer interface to an undoped intrinsic zone between the p- and n-type regions of the active layer in the LECs, which qualifies the LEC type devices as a cost-effective approach to the single layer color-stable blue emitting devices.
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85.60.Jb Light-emitting devices
82.47.Jk Photoelectrochemical cells, photoelectrochromic and other hybrid electrochemical energy storage devices
85.60.Ha Photomultipliers; phototubes and photocathodes
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds

Effects of surface topology on the formation of oxide islands on Cu surfaces

Guangwen Zhou, Liang Wang, and Judith C. Yang

J. Appl. Phys. 97, 063509 (2005); http://dx.doi.org/10.1063/1.1861147 (6 pages) | Cited 2 times

Online Publication Date: 7 March 2005

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We examined the effects of surface topology on the nucleation and growth of Cu2O oxide islands during the initial oxidation stages of Cu(100) and Cu(110) surfaces by in situ ultrahigh vacuum transmission electron microscopy and ex situ atomic force microscopy. Our observations indicate that nucleation of three dimensional oxide islands on single crystal surfaces is homogenous, surface defects and dislocations play a very limited role as preferential sites for oxide nucleation. On the other hand, grain boundaries are the preferential sites for oxide nucleation and the oxide islands formed along the grain boundaries show a faster growth rate than that on flat Cu surface. The oxidation on the faceted Cu(110) surface results in heterogeneous nucleation of oxide islands in the facet valleys and one-dimensional growth along the intersection direction of the facets.
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68.55.-a Thin film structure and morphology
81.65.Mq Oxidation
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Bx Metals, semimetals, and alloys
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries
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)
68.37.Ps Atomic force microscopy (AFM)

(In,Ga)As sidewall quantum wires on shallow-patterned InP (311)A

D. Zhou, R. Nötzel, Q. Gong, P. Offermans, P. M. Koenraad, P. J. van Veldhoven, F. W. M. van Otten, T. J. Eijkemans, and J. H. Wolter

J. Appl. Phys. 97, 063510 (2005); http://dx.doi.org/10.1063/1.1862763 (5 pages) | Cited 3 times

Online Publication Date: 7 March 2005

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(In,Ga)As sidewall quantum wires (QWires) are realized by chemical beam epitaxy along [01-1] mesa stripes on shallow-patterned InP (311)A substrates. The QWires exhibit strong lateral carrier confinement due to larger thickness and In composition compared to the adjacent quantum wells, as determined by cross-sectional scanning-tunneling microscopy and microphotoluminescence (micro-PL) spectroscopy. The PL of the (In,Ga)As QWires with InP and quaternary (Ga,In)(As,P) barriers reveals narrow linewidth, high efficiency, and large lateral carrier confinement energies of 60–70 meV. The QWires are stacked in growth direction with identical PL peak emission energy. The PL emission energy is not only controlled by the (In,Ga)As layer thickness but also by the patterned mesa height. Stacked (In,Ga)As QWires with quaternary barriers exhibit room temperature PL emission at 1.55 μm in the technologically important wavelength region for telecommunication applications.
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81.07.Vb Quantum wires
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.La Quantum wires (patterned in quantum wells)
73.21.Hb Quantum wires
78.67.Lt Quantum wires
78.55.Cr III-V semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Positron beam studies of argon-irradiated polycrystal α-Zr

Chunlan Zhou, Xiaoyang Liu, Chuangxin Ma, Baoyi Wang, Zhiming Zhang, and Long Wei

J. Appl. Phys. 97, 063511 (2005); http://dx.doi.org/10.1063/1.1833573 (7 pages) | Cited 3 times

Online Publication Date: 9 March 2005

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Doppler broadening spectroscopy was performed using a variable-energy positron beam to investigate the effect of defects induced by 150-keV Ar-ion-irradiated α-Zr bulk material. S parameter in the damaged layer of the as-irradiated sample induced by ion irradiation increased with the increasing implantation dose. Isochronal annealing between 350 and 800 °C in vacuum studies was carried out to investigate the thermal stability of defects in the oxide surface and damaged layer for low-dose (1×1014 cm2) and high-dose (1×1016 cm2) irradiated samples. The results of S-W plot measured at different annealing temperatures showed that the positron-trapping center had changed. The Ar-decorated voids or vacancies, which formed in high-dose implantation samples by Ar ions combining with open-volume defects, are stable and do not recover until at high annealing temperatures. Comparing the annealing behavior of the high-dose and low-dose implantation samples show that the recovery process of open-volume defects such as vacancies and voids will be delayed by the excess Ar concentration.
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78.70.Bj Positron annihilation
61.72.J- Point defects and defect clusters
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.80.Fe Electron and positron radiation effects
61.80.Jh Ion radiation effects
61.82.Ms Insulators
61.72.up Other materials
73.20.Hb Impurity and defect levels; energy states of adsorbed species
61.72.S- Impurities in crystals
81.40.Gh Other heat and thermomechanical treatments

Microbeam high-resolution x-ray diffraction in strained InGaAlAs-based multiple quantum well laser structures grown selectively on masked InP substrates

A. A. Sirenko, A. Kazimirov, R. Huang, D. H. Bilderback, S. O’Malley, V. Gupta, K. Bacher, L. J. P. Ketelsen, and A. Ougazzaden

J. Appl. Phys. 97, 063512 (2005); http://dx.doi.org/10.1063/1.1862769 (7 pages) | Cited 14 times

Online Publication Date: 9 March 2005

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Structural and optical properties of the InGaAlAs-based multiple quantum well (MQW) 1.3 μm laser structures produced on InP (001) substrates by metal organic vapor phase epitaxy (MOVPE) technique in the regime of selective area growth (SAG) have been studied. An x-ray beam of 10 μm diameter generated by a microbeam high-resolution x-ray diffraction (μ-HRXRD) setup based on an imaging one-bounce capillary optic and a three-bounce channel cut Si(004) analyzer crystal has been utilized to measure the diffraction curves from MQW structures grown between oxide mask stripes. The high angular resolution achieved in our experiments allowed accurate measurements of θ–2θ scans over a broad range of angles that was necessary for utilization of fitting algorithms for quantitative analysis of the strain and thickness of individual layers in the MQW structures. The thickness and strain variations in the quantum well and the barrier layers of the MQW SAG structure have been analyzed as a function of the oxide mask width in the range of 15–140 μm with the gap between the oxide masks in the range of 15–80 μm. Dramatic structural changes from the perfect quality MQW’s in the SAG structures with the narrow oxide masks (less than 45 μm) to the strain relaxed MQW’s in the SAG regime with the wide oxide masks (more than 50 μm) have been experimentally detected. The spontaneous photoluminescence emission between 1.3 and 1.51 μm from the simultaneously grown InGaAlAs-based MQW SAG laser structures have been measured. Using a combination of μ-HRXRD results with the microphotoluminescence data, the optimal SAG mask parameters for the growth of integrated InGaAlAs-based optoelectronic light-emitting components and devices have been determined.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells
78.55.Cr III-V semiconductors
68.65.Fg Quantum wells
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Mössbauer effect study of correlation between structure and exchange-bias effect in ferromagnetic Fe∕antiferromagnetic FeSn2 bilayers

V. E. Kuncser, F. Stromberg, M. Acet, and W. Keune

J. Appl. Phys. 97, 063513 (2005); http://dx.doi.org/10.1063/1.1858879 (10 pages) | Cited 5 times

Online Publication Date: 9 March 2005

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Antiferromagnetic (AF) FeSn2(001) epitaxial and polycrystalline layers were grown in ultrahigh vacuum under various conditions on clean InSb(001) substrates and covered by polycrystalline ferromagnetic Fe layers, forming a new system with exchange bias. Isotopically enriched math- and mathSn2-tracer layers were placed on either side of the Fe/FeSn2 interface for a microscopic investigation of the spin structure and atomic interdiffusion phenomena in near-interfacial regions by math conversion electron Mössbauer spectroscopy (CEMS) at room temperature and T = 10 K. Several spectral components, assigned to pure bcc Fe, Sn-containing bcc Fe, AF-ordered FeSn2, and paramagnetic FeSn2 were resolved in the CEM spectra. Evidence is provided for interdiffusion across the interface. The temperature dependence of the exchange-bias field HE was measured by magnetometry. The CEMS data provide evidence for a correlation between HE at low T and chemical disorder (defects) in the FeSn2 films via the intensity of the paramagnetic line. These results support the assumption that exchange bias is related to the presence of AF domains formed via magnetic defects in the antiferromagnet. The T dependence of HE suggests interfacial exchange-coupling energies higher than the AF wall energy.
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75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.J- Point defects and defect clusters
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
68.35.Fx Diffusion; interface formation
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
81.40.Gh Other heat and thermomechanical treatments
75.60.Ch Domain walls and domain structure

Polarity effect of electromigration on kinetics of intermetallic compound formation in Pb-free solder V-groove samples

H. Gan and K. N. Tu

J. Appl. Phys. 97, 063514 (2005); http://dx.doi.org/10.1063/1.1861151 (10 pages) | Cited 69 times

Online Publication Date: 9 March 2005

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Intermetallic compound (IMC) formation is critical for the reliability of microelectronic interconnections, especially for flip chip solder joints. In this article, we investigate the polarity effect of electromigration on kinetics of IMC formation at the anode and the cathode in solder V-groove samples. We use V-groove solder line samples, with width of 100 μm and length of 500–700 μm, to study interfacial IMC growth between Cu electrodes and Sn-3.8Ag-0.7Cu (in wt %) solder under different current density and temperature settings. The current densities are in the range of 103 to 104 A/cm2 and the temperature settings are 120, 150, and 180 °C. While the same types of IMCs, Cu6Sn5 and Cu3Sn, form at the solder/Cu interfaces independent of the passage of electric current, the growth of the IMC layer has been enhanced by electric current at the anode and inhibited at the cathode, in comparison with the no-current case. We present a kinetic model, based on the Cu mass transport in the sample, to explain the growth rate of IMC at the anode and cathode. The growth of IMC at the anode follows a parabolic growth rule, and we propose that the back stress induced in the IMC plays a significant role. The model is in good agreement with our experimental data. We then discuss the influence of both chemical force and electrical force, and their combined effect on the IMC growth with electric current.
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85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.Fx Diffusion; interface formation
66.30.Qa Electromigration
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Ct Interface structure and roughness

Conduction mechanisms in ion-irradiated InGaAs layers

L. Joulaud, J. Mangeney, N. Chimot, P. Crozat, G. Fishman, and J. C. Bourgoin

J. Appl. Phys. 97, 063515 (2005); http://dx.doi.org/10.1063/1.1861966 (7 pages) | Cited 8 times

Online Publication Date: 11 March 2005

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The electrical and optical properties of H+- and Au+-irradiated InGaAs layers were studied using Hall-effect, van der Pauw, and relaxation-time measurements. Comparing the different results allows us to obtain information on the nature of the defects created by these two irradiations. Proton irradiation introduces donor-acceptor paired defects. Gold-ion irradiation creates neutral defect clusters and ionized point defects. The carrier mobilities in all of the irradiated materials are degraded, decreasing with increasing irradiation dose. A scattering model taking into account the paired defects is developed and the mobility evolution calculated from this model agrees with the experimental data of both annealed and unannealed samples. The photocurrent spectra reveal a metallic conduction in the band gap in the case of light-ion irradiation, while such type of conduction does not appear for heavy-ion irradiation. This metallic conduction is a consequence of band tailing induced by shallow defects and vanishes when the material is annealed at 400 °C. The proton irradiation-induced defects appear to be related to the EL-2-like defects.
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78.66.Fd III-V semiconductors
61.82.Fk Semiconductors
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.55.Eq III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
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