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15 Mar 2006

Volume 99, Issue 6, Articles (06xxxx)

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Generation of frequency tunable polarization entangled photon pairs

Atsushi Yabushita and Takayoshi Kobayashi

J. Appl. Phys. 99, 063101 (2006); http://dx.doi.org/10.1063/1.2183355 (7 pages) | Cited 3 times

Online Publication Date: 23 March 2006

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Photon pairs with correlated frequencies from an optical parametric system were generated by a continuous wave pump focused on a type-II nonlinear crystal with polarization entanglement. The polarization entanglement of the frequency resolved photons was measured under several typical configurations. By optimizing a condition, the degree of polarization entanglement was improved substantially. We proposed the application of the system, which can be used as a light source of wavelength division multiplexing quantum key distribution, optimizing the configuration of the photon-pair generation.
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42.65.Lm Parametric down conversion and production of entangled photons
42.50.Dv Quantum state engineering and measurements

Micropropulsion devices based on molecular acceleration by pulsed optical lattices

Mikhail N. Shneider, Sergey F. Gimelshein, and Peter F. Barker

J. Appl. Phys. 99, 063102 (2006); http://dx.doi.org/10.1063/1.2183410 (5 pages) | Cited 2 times

Online Publication Date: 24 March 2006

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The ability of a traveling periodic optical potential to increase the thrust and specific impulse of microthrusters is investigated. Two flow regimes, high density and low density, are considered. The thrust from a micronozzle, with a stagnation pressure of 1 atm and temperature of 300 K, can be increased by more than an order of magnitude. These conditions can be achieved for a constant velocity lattice, produced by two near counterpropagating optical fields that are focused into the nozzle throat. A propulsion system that operates in low-density regime and is driven by molecules trapped by an accelerating optical lattice is proposed. It is shown that such a system has a potential to achieve a specific impulse of thousands of seconds.
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37.10.Mn Slowing and cooling of molecules
37.10.Pq Trapping of molecules
47.60.-i Flow phenomena in quasi-one-dimensional systems

Impact of absorption mechanisms on Kerr-nonlinear resonator behavior

Gino Priem, Peter Bienstman, Geert Morthier, and Roel Baets

J. Appl. Phys. 99, 063103 (2006); http://dx.doi.org/10.1063/1.2184432 (8 pages) | Cited 3 times

Online Publication Date: 28 March 2006

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The effect of both single-photon and two-photon absorption mechanisms on the Kerr-nonlinear behavior of resonant structures is investigated using a semianalytical, one-dimensional model. In particular, two-photon effects may severely degrade the ultrafast, nonlinear potential of these structures. Based on this model, the feasibility of Kerr-nonlinear operation is derived for the AlGaAs and Si material systems.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Analytical and numerical calculations of the dispersion characteristics of two-dimensional dielectric photonic band gap structures

Ksenia Samokhvalova, Chiping Chen, and Bao-Liang Qian

J. Appl. Phys. 99, 063104 (2006); http://dx.doi.org/10.1063/1.2186385 (6 pages) | Cited 8 times

Online Publication Date: 30 March 2006

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An exact analytical dispersion relation is derived for transverse-magnetic modes with kz = 0 in a particular two-dimensional rectangular photonic band gap structure. The dispersion relation is analyzed, and the dispersion characteristics are determined. Analytical results are compared with results from the Massachusetts Institute of Technology Photonic Band Gap Structure Simulator (PBGSS) code. The error tolerance in the PBGSS code is established. Finally, the attenuations of modes with frequencies in global band gaps are computed analytically.
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42.70.Qs Photonic bandgap materials
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Ion debris characterization from a z-pinch extreme ultraviolet light source

Erik L. Antonsen, Keith C. Thompson, Matthew R. Hendricks, Darren A. Alman, Brian E. Jurczyk, and D. N. Ruzic

J. Appl. Phys. 99, 063301 (2006); http://dx.doi.org/10.1063/1.2175471 (8 pages) | Cited 18 times

Online Publication Date: 21 March 2006

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An XTREME Technologies XTS 13-35 extreme ultraviolet (EUV) light source creates a xenon z pinch that generates 13.5 nm light. Due to the near x-ray nature of light at this wavelength, extremely smooth metal mirrors for photon collection must be employed. These are exposed to the source debris. Dissolution of the z-pinch gas column results in high-energy ion and neutral release throughout the chamber that can have adverse effects on mirror surfaces. The XTREME commercial EUV emission diagnostic chamber was designed to maximize diagnostic access to the light and particulate emissions from the z pinch. The principal investigation is characterization of the debris field and the erosive effects on optics present. Light emission from the z pinch is followed by ejection of multiply charged ions and fast neutral particles that make up an erosive flux to chamber surfaces. Attenuation of this erosive flux to optical surfaces is attempted by inclusion of a debris mitigation tool consisting of foil traps and neutral buffer gas flow. Characterization of the z-pinch ejecta is performed with a spherical sector energy analyzer (ESA) that diagnoses fast ion species by energy-to-charge ratio using ion time-of-flight (ITOF) analysis. This is used to evaluate the debris tool’s ability to divert direct fast ions from impact on optic surfaces. The ITOF-ESA is used to characterize both the energy and angular distribution of the direct fast ions. Xe+ up to Xe+4 ions have been characterized along with Ar+ (the buffer gas used), W+, Mo+, Si+, Fe+, and Ni+. Energy spectra for these species from 0.5 up to 13 keV are defined at 20° and 30° from the pinch centerline in the chamber. Results show a drop in ion flux with angular increase. The dominant species is Xe+ which peaks around 8 keV. Ion flux measured against buffer gas flow rate suggests that the direct fast ion population is significantly attenuated through increases in buffer gas flow rate. This does not address momentum transfer from scattered ions or fast neutral particles. These results are discussed in the context of other investigations on the effects of total particle flux to normal incidence mirror samples exposed for 1×107 pulses. The samples (Si/Mo multilayer with Ru capping layer, Au, C, Mo, Pd, Ru, and Si) were exposed to the source plasma with 75% argon flow rate in the debris mitigation tool and surface metrology was performed using x-ray photoelectron spectroscopy, atomic force microscopy, x-ray reflectivity, and scanning electron microscopy to analyze erosion effects on mirrors. These results are compared to the measured direct ion debris field.
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52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.50.Dg Plasma sources
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Tx Emission, absorption, and scattering of particles
52.40.Hf Plasma-material interactions; boundary layer effects
52.70.Nc Particle measurements

Spatial distribution of soft x-ray line emissions from aluminum plasma excited by a pair of femtosecond-laser pulses

Yasuaki Okano, Katsuya Oguri, Tadashi Nishikawa, and Hidetoshi Nakano

J. Appl. Phys. 99, 063302 (2006); http://dx.doi.org/10.1063/1.2180433 (4 pages) | Cited 3 times

Online Publication Date: 21 March 2006

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We measured the time-integrated, spatially resolved spectra of soft x rays emitted from laser-induced aluminum plasma to characterize its spatial features. The plasma was excited by an intense femtosecond-laser pulse with a controlled artificial prepulse at intensities of 9.9×1015 and 6.4×1014 W/cm2, respectively. The dependence of the spectra on the time intervals between the main pulse and the prepulse was obtained for delay times of 0–3 ns. The strongest emissions in soft x-ray range occurred in a narrow region less than 50 μm from the target surface. In contrast to the continuum spectrum, the prepulse technique causes the Al3+2p6−2p53s emission to extend more than 600 μm from the target surface. We showed that the line emission can be separated spatially from the other continuum component of the emission spectra and that the extension length increased with increases in the pulse-separation time.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.38.Ph X-ray, γ-ray, and particle generation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Characterization of a channel spark discharge and the generated electron beam

Ya. E. Krasik, S. Gleizer, K. Chirko, J. Z. Gleizer, J. Felsteiner, V. Bernshtam, and F. C. Matacotta

J. Appl. Phys. 99, 063303 (2006); http://dx.doi.org/10.1063/1.2180453 (14 pages) | Cited 5 times

Online Publication Date: 22 March 2006

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We report on an experimental study of a channel spark discharge (CSD) and the generated electron beam. The CSD was operated at a discharge voltage Ud ⩽ 30 kV and a discharge current Id ⩽ 3.5 kA. The CSD system consists of a glass tube placed between a hollow cathode and a grounded anode electrode. The parameters of the CSD operation, the potential distribution along the glass tube, and the generated beam were studied by electrical, optical, and spectroscopic diagnostics in the Ar gas pressure range of P = 0.005–2 Pa. At P ≥ 0.5 Pa, electrons with energy ∼ eUd appeared prior to the start of the main CSD with a current amplitude ⩽ 10−4Id. These high-energy electrons are responsible for the initiation of the CSD inside the glass tube. The generation of the electron beam which was composed of low-energy electrons with a current amplitude up to 3 kA occurred during a fast fall in the discharge voltage. Decreasing the Ar gas pressure below 0.1 Pa allows one to increase significantly the beam duration and the part of the high-energy electrons in the beam, and to increase the efficiency of the electron beam generation up to 75%. The high-current CSD inside the glass tube is accompanied by the formation of a plasma consisting of protons, Ar II, Ar III, C II-IV, and O II-IV ions. The plasma electron density and temperature were found to be in the ranges of 1015–1016 cm−3 and 10-15 eV, respectively.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Hc Glow; corona
52.70.Ds Electric and magnetic measurements
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.50.Dg Plasma sources
52.25.Tx Emission, absorption, and scattering of particles

Effect of ambient pressure on laser ablation and plume expansion dynamics: A numerical simulation

Zhaoyang Chen, Davide Bleiner, and Annemie Bogaerts

J. Appl. Phys. 99, 063304 (2006); http://dx.doi.org/10.1063/1.2182078 (9 pages) | Cited 14 times

Online Publication Date: 23 March 2006

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A comprehensive numerical model is applied to the study of the effect of ambient pressure in laser ablation, more specifically on the copper target heating, melting and vaporization, and the resulting plume expansion in the helium gas, as well as on plasma formation in the plume. Under the laser pulse condition investigated [5 ns full width at half maximum (FWHM) and 109 W/cm2 peak irradiance], the calculated results show that the characteristics of the surface temperature and the evaporation depth are very similar even when the ambient pressure varies greatly. The influence of the ambient pressure on the fraction of absorbed laser energy is also small. The maximum ablated material vapor density in the plume is influenced slightly by the different pressures. Before 40 ns, the maximum plume temperature for various ambient pressures is in the order of a few 104 K. However, the effect of ambient pressure on the plume length is quite large. A specific calculation for a Gaussian-shaped laser pulse with 6 ns FWHM and 2.76×109 W/cm2 peak irradiance is made. The calculated evaporation depth agrees well with the experimental data. Therefore, the model can be useful to predict trends in target and plume (plasma) characteristics, which are difficult to obtain experimentally for various ambient pressures.
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52.38.Mf Laser ablation
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.65.Kj Magnetohydrodynamic and fluid equation
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

Radio frequency glow discharge source with integrated voltage and current probes used for evaluation of discharge parameters

L. Wilken, V. Hoffmann, and K. Wetzig

J. Appl. Phys. 99, 063305 (2006); http://dx.doi.org/10.1063/1.2182077 (13 pages) | Cited 5 times

Online Publication Date: 28 March 2006

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A radio frequency (rf) Grimm-type glow discharge source for the chemical analysis of solid samples, with integrated voltage and current probes, was developed. All elements of a plasma equivalent circuit are determined from the measured current-voltage characteristics. The procedure is based on the independent evaluation of the ion current and electron current region. The physical meaning of the parameters is investigated by comparisons with measurements from dc glow discharges. We found that the reduced rf current of the powered electrode is comparable to the reduced current in dc discharges. A formula is developed that corrects the reduced current due to gas heating. The sheath thickness at the powered rf electrode is evaluated and is between 75 and 1100 μm. The voltage of the bulk plasma is in the range 2–15 V, and the resistance is between 30 and 400 Ω. The bulk plasma consumes about 3% of the total power, and the reduced voltage is comparable to the reduced electrical field in the positive column of direct current discharges. The sheath voltage at the grounded electrode is in the range 25–100 V, the capacities are between 10 and 400 pF, and the resistances are in the range 100 Ω–5000 Ω. We also found invariants for the evaluated sheath parameters.
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52.80.Pi High-frequency and RF discharges
52.80.Hc Glow; corona
52.50.Dg Plasma sources
52.70.Ds Electric and magnetic measurements
52.40.Kh Plasma sheaths
52.25.Fi Transport properties
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Sapphire: A kinking nonlinear elastic solid

S. Basu, M. W. Barsoum, and S. R. Kalidindi

J. Appl. Phys. 99, 063501 (2006); http://dx.doi.org/10.1063/1.2179974 (7 pages) | Cited 19 times

Online Publication Date: 16 March 2006

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Kinking nonlinear elastic (KNE) solids are a recently identified large class of solids that deform fully reversibly by the formation of dislocation-based kink bands [ Barsoum et al. Phys. Rev. Lett. 92, 255508 (2004) ]. We further conjectured that a high c/a ratio—that ensures that only basal slip is operative—is a sufficient condition for a solid to be KNE. The c/a ratio of sapphire is 2.73 and thus, if our conjecture is correct, it should be a KNE solid. Herein by repeatedly loading—up to 30 times—the same location of sapphire single crystals of two orientations—A and C—with a 1 μm radius spherical nanoindenter, followed by atomic force microscopy, we showed that sapphire is indeed a KNE solid. After pop-ins of the order of 100 nm, the repeated loadings give rise to fully reversible, reproducible hysteresis loops wherein the energy dissipated per unit volume per cycle Wd is of the order of 0.5 GJ/m3. Wd is due to the back and fro motion of the dislocations making up the incipient kink bands that are fully reversible. The results presented here strongly suggest that—like in graphite and mica—kink bands play a more critical role in the room temperature constrained deformation of sapphire than had hitherto been appreciated. Our interpretation is also in agreement with, and can explain most, recent nanoindentation results on sapphire.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.20.D- Elasticity
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Ps Atomic force microscopy (AFM)

Finite-difference time-domain simulation of heterostructures with inclusion of arbitrarily complex geometry

Abdelilah Mejdoubi and Christian Brosseau

J. Appl. Phys. 99, 063502 (2006); http://dx.doi.org/10.1063/1.2171771 (14 pages) | Cited 11 times

Online Publication Date: 17 March 2006

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Currently, there is a great interest in tailoring the polarization properties of composite materials with the goal of controlling the dielectric behavior. This paper reports finite-difference time-domain (FDTD) modeling of the dielectric behavior of two-dimensional (2D) lossless two-phase heterostructures. More specifically, we present extensive results of 2D FDTD computations on the quasistatic effective permittivity of a single inclusion, with arbitrarily complex geometry (regular polygons and fractals), embedded in a plane. The uniaxial perfectly matched layer-absorbing boundary condition is found adequate for truncating the boundary of the 2D space because it leads to only very small backreflections. The effectiveness of the method is demonstrated by the variety of geometries modeled, i.e., regular polygons and fractals, and permittivity contrast ratios which allows us to distinguish between effects of surface fraction and effects of morphology. Our calculations show that geometrical effects can give rise to significant modifications of the surface fraction dependence of the permittivity. The results are compared with Maxwell-Garnett (MG) and symmetric Bruggeman (SBG) formulas. As expected the effective permittivity in the situations considered here deviates from the MG and SBG results at high surface fractions and/or high permittivity ratios between the inclusion and the host medium. In addition, the results show that a two-phase composite containing a fractal-boundary inclusion, e.g., Koch’s snowflake, can have a permittivity which is several tens of percent lower between the first and the fourth iteration of the structure at a fixed perimeter-to-surface ratio. This feature is consistent with the fact that as the surface fraction becomes higher, the inclusion rough boundaries dominate the overall geometry. We believe that simplified modeling such as the modeling done here can serve as a useful purpose in understanding the interplay between the structure and dielectric function and in engineering multifunctional materials at the nanoscale.
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77.22.Ch Permittivity (dielectric function)
05.45.Df Fractals
02.70.Bf Finite-difference methods

Formation of self-organized anisotropic polymer structures by confined dynamic instability

S. Joon Kwon

J. Appl. Phys. 99, 063503 (2006); http://dx.doi.org/10.1063/1.2180408 (7 pages) | Cited 3 times

Online Publication Date: 21 March 2006

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We report on the formation of self-organized anisotropic structures of the polymer thin films induced by the wave interaction-driven dynamic instability confined by corrugated elastomeric molds. In the initial stage of the morphological instability, self-organized anisotropic structures such as a regularly undulated surface wave pattern formed on the ridge followed by the formation of a highly ordered array of droplets on the wall and a surface wave on the groove. The self-organization in the initial stage is dominated by the formation of the surface wave on the ridge accompanying a period of half the first harmonic wavelength of the mold corrugation. In the final stage of the instability, undulated polymer structure on the ridge is transformed into a periodic array of droplets with the first harmonic wavelength of the mold corrugation, while the undulation in the polymer layer on the groove is nearly sustained. The self-organized anisotropic polymer structures can provide simpler methods of fabricating complicated three-dimensional polymeric structures.
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68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
61.41.+e Polymers, elastomers, and plastics
68.35.B- Structure of clean surfaces (and surface reconstruction)

Temperature-dependent photoluminescence from elemental sulfur species on ZnS nanobelts

Changhui Ye, Xiaosheng Fang, Ming Wang, and Lide Zhang

J. Appl. Phys. 99, 063504 (2006); http://dx.doi.org/10.1063/1.2181311 (4 pages) | Cited 14 times

Online Publication Date: 21 March 2006

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We report the experimental study of the temperature-dependent photoluminescence from elemental sulfur species on zinc sulfide nanobelts. The green band emission shows an anomalous blueshift-redshift transition and the half-width undergoes a narrowing-broadening transition with decreasing temperature. We observed that the thermal quenching of the integrated intensity of the green band was suppressed. The anomalous behavior can be attributed to strong carrier localization in the unsaturated dangling orbitals of the elemental sulfur. In addition, the blue band in the undoped ZnS nanobelts is also related to the surface sulfur species that is different from the previously reported self-activation mechanism.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
81.40.Gh Other heat and thermomechanical treatments

Laser oscillation from hexagonal crystals of a thiophene∕phenylene co-oligomer

Kouki Shimizu, Yuji Mori, and Shu Hotta

J. Appl. Phys. 99, 063505 (2006); http://dx.doi.org/10.1063/1.2181278 (4 pages) | Cited 21 times

Online Publication Date: 21 March 2006

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The characteristics of the unusually narrowed emission from hexagon BP1T crystals were investigated by photopumping them with a line laser beam. The wavelengths and strengths of the emission lines sensitively depended on the position and the angle of the crystal. The threshold of the excitation fluence decreases inversely proportional to the crystal length. We have concluded that the unusually narrowed emission is the laser oscillation by laser cavity resonance within a waveguide. The shape and size of the excitation laser beam play an important role in the laser oscillation.
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42.55.Px Semiconductor lasers; laser diodes
42.70.Hj Laser materials
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Optical characterization of ZnSe epilayers and ZnCdSe/ZnSe quantum wells grown on Ge/Ge0.95Si0.05/Ge0.9Si0.1/Si virtual substrates

J. T. Ku, M. C. Kuo, J. L. Shen, K. C. Chiu, T. H. Yang, G. L. Luo, C. Y. Chang, Y. C. Lin, C. P. Fu, D. S. Chuu, C. H. Chia, and W. C. Chou

J. Appl. Phys. 99, 063506 (2006); http://dx.doi.org/10.1063/1.2181267 (6 pages) | Cited 3 times

Online Publication Date: 22 March 2006

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Several approaches have been employed to grow high-quality ZnSe epilayers on Ge/Ge0.95Si0.05/Ge0.9Si0.1/Si virtual substrates. The ZnSe epilayers were characterized by photoluminescence spectroscopy. Migration enhanced epitaxy and inserting an in situ thermal annealing ZnSe buffer layer effectively reduced the intensity of deep level emissions from the ZnSe epilayer grown on a 6°-tilted Ge/Ge0.95Si0.05/Ge0.9Si0.1/Si virtual substrate. Optimized conditions for growing high-quality ZnSe were used to deposit ZnCdSe/ZnSe multiple quantum wells on Ge/Ge0.95Si0.05/Ge0.9Si0.1/Si virtual substrates. Photoluminescence spectroscopy revealed quantum-confinement effect in the ZnCdSe multiple quantum wells. The evolution of the exciton emission peak energy and the linewidth as a function of temperature indicate a low density of localized sites in the sample with a well width of 1 nm. In the high-temperature regime, the thermal quenching of the excitonic emission intensity from ZnCdSe quantum well structures was governed by the thermal activation of carriers from quantum-well-confined states into barrier states.
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78.66.Hf II-VI semiconductors
78.67.De Quantum wells
78.55.Et II-VI semiconductors
78.20.Jq Electro-optical effects
73.21.Fg Quantum wells
61.72.Cc Kinetics of defect formation and annealing

Raman study of the random ZnTe–BeTe mixed crystal: Percolation model plus multimode decomposition

O. Pagès, T. Tite, A. Chafi, D. Bormann, O. Maksimov, and M. C. Tamargo

J. Appl. Phys. 99, 063507 (2006); http://dx.doi.org/10.1063/1.2183349 (8 pages) | Cited 3 times

Online Publication Date: 22 March 2006

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The Verleur and Barker-like multiphonon description proposed for the refined understanding of the two-mode transverse optical (TO) and longitudinal optical (LO) Raman responses from the stiff∕short Be–Se bond in the percolation range (0.19 ⩽ Be ⩽ 0.81) of the random BeSe–ZnSe mixed crystal [ O. Pagès et al., Phys. Rev. B 70, 155319 (2004) ] is extended to the similar Be–Te bond in the percolation range of the random BeTe–ZnTe mixed crystal. Moreover this description is shown to remain valid just outside the percolation range, in spite of appearances. We deduce that it is not activated by the close intermixing of the stiff and soft continua at the mesoscopic scale but relies directly on the contrast in the bond properties at the microscopic scale. The whole study is supported by extensive ZnBeTe Raman data, and full contour modeling of the TO and LO Raman line shapes by using our phenomenological 1‐bond→2‐mode percolation model. Care is taken that our ZnBe(Se,Te) epitaxial layers undergo large substrate-induced residual biaxial strains at the two edges of the percolation range. This generates significant phonon shifts, which have to be taken into account.
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78.66.Hf II-VI semiconductors
68.60.Bs Mechanical and acoustical properties
78.30.Fs III-V and II-VI semiconductors
63.20.K- Phonon interactions

Photoluminescence study of potential fluctuations in thin layers of Cu(In0.75Ga0.25)(SySe1−y)2

S. A. Schumacher, J. R. Botha, and V. Alberts

J. Appl. Phys. 99, 063508 (2006); http://dx.doi.org/10.1063/1.2180429 (8 pages) | Cited 4 times

Online Publication Date: 22 March 2006

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Thin layers of the pentenary material Cu(In,Ga)(S,Se)2 (CIGSSe) are studied using photoluminescence (PL) spectroscopy. The layers were produced by a two-stage deposition process, which produces thin chalcopyrite films with a high degree of compositional uniformity throughout the thickness of the layer. It is shown that potential fluctuations, caused by compensation and high concentrations of defects, dominate the PL behavior of the investigated layers. This is inferred from a number of PL studies such as variable temperature and excitation power measurements. It is deduced that the average amplitude of fluctuations increases with increasing sulfur mole fraction S/(Se+S). Thus, sulfur incorporation increases the degree of compensation (and hence the charged defect concentration). From the strong asymmetry and the observed weak shift of the low energy tails in the PL spectra with increasing sulfur content, it is also concluded that a significant fraction of defect states associated with the quaternary CIGSSe is still present in the pentenary layers.
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78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Ht Other nonmetals
61.72.-y Defects and impurities in crystals; microstructure

On the origin of the Staebler-Wronski effect

Thomas Krüger

J. Appl. Phys. 99, 063509 (2006); http://dx.doi.org/10.1063/1.2181671 (4 pages) | Cited 1 time

Online Publication Date: 22 March 2006

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The parametrization of our recently proposed model of the Staebler-Wronski effect (SWE) is improved, which leads to an even better agreement with the experimental photoconductivity of light-soaked a‐Si:H. The numerical solution of the essential equation exhibits well the typical SWE behavior, and it will be shown that previously raised arguments against our model are unfounded.
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72.40.+w Photoconduction and photovoltaic effects

Strain and composition of ultrasmall Ge quantum dots studied by x-ray scattering and in situ surface x-ray absorption spectroscopy

R. Dujardin, V. Poydenot, T. U. Schülli, G. Renaud, O. Ulrich, A. Barski, M. Derivaz, S. Colonna, and T. Metzger

J. Appl. Phys. 99, 063510 (2006); http://dx.doi.org/10.1063/1.2181277 (7 pages) | Cited 4 times

Online Publication Date: 22 March 2006

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Investigations of the structural properties of ultrasmall Ge dots, grown through a thin silicon oxide layer on Si(001), have been performed by combining (i) grazing incidence x-ray diffraction, (ii) grazing incidence small angle x-ray scattering (GISAXS), and (iii) surface extended x-ray absorption fine structure (SEXAFS). Grazing incidence x-ray diffraction observations show that the dots are highly strained to the Si(001) substrate. The dot shape and composition, as determined by GISAXS experiments and in situ SEXAFS, strongly depend on the thickness and the composition of the silicon oxide layer covering the surface of the silicon substrate. Ge dots grown through 1.2 nm thick SiO2 are round shaped with a Ge content of about 60% whereas dots grown through 0.3 nm thick SiOx are facetted and composed of almost pure Ge.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.05.Cy Elemental semiconductors
78.70.Ck X-ray scattering
78.70.Dm X-ray absorption spectra

Dielectric function and electric properties of germanium thin films prepared by gold mediated crystallization

Maria M. Giangregorio, Maria Losurdo, Marianna Ambrico, Pio Capezzuto, Giovanni Bruno, and Leander Tapfer

J. Appl. Phys. 99, 063511 (2006); http://dx.doi.org/10.1063/1.2180407 (6 pages) | Cited 3 times

Online Publication Date: 24 March 2006

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Crystallization of hydrogenated amorphous germanium (a‐Ge:H) thin films deposited by plasma enhanced chemical vapor deposition using the GeH4 and H2 precursors has been investigated. A comparative analysis of the kinetics of the thermal crystallization by annealing to 650 °C and of the gold-mediated crystallization (Au-MMC) is carried out. The impact of the Au-MMC on the microcrystalline Ge film microstructure and electrical properties is discussed. The Au thin layer results in a more dense and ordered structure with lower roughness of the microcrystalline Ge films. In order to describe the Ge crystallization kinetics, the dielectric functions of a‐Ge:H and microcrystalline germanium μc‐Ge have also been determined by spectroscopic ellipsometry in the range of 0.75−6.0 eV and parametrized using the Tauc-Lorentz dispersion equation.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.61.Cw Elemental semiconductors
68.55.A- Nucleation and growth
64.70.D- Solid-liquid transitions

Probing residual strain in InGaAs/GaAs micro-origami tubes by micro-Raman spectroscopy

A. Bernardi, A. R. Goñi, M. I. Alonso, F. Alsina, H. Scheel, P. O. Vaccaro, and N. Saito

J. Appl. Phys. 99, 063512 (2006); http://dx.doi.org/10.1063/1.2183353 (6 pages) | Cited 7 times

Online Publication Date: 24 March 2006

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We have experimentally investigated nanostructures consisting of free-standing microtubes with diameters in the micrometer range fabricated by rolling-up InGaAs/GaAs bilayers grown by molecular-beam epitaxy on a GaAs substrate. The formation of the microtubes is powered by the built-in strain in the InGaAs layer and they develop after releasing the bilayer structure from the substrate by selective etching. Through micro-Raman spectroscopy we were able to detect the residual strain of the microtube, which results in a frequency shift of phonon modes measured on the tube as compared with reference unstrained material. We developed a simple elastic model to describe the measured phonon frequency shifts, from which we estimate the strain status of the microtube. Results demonstrate the power of Raman spectroscopy as a diagnostic tool for engineering of strain-driven self-positioning microelectromechanical systems.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.30.Fs III-V and II-VI semiconductors
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
61.46.-w Structure of nanoscale materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Superscrew dislocations in silicon carbide: Dissociation, aggregation, and formation

Xianyun Ma

J. Appl. Phys. 99, 063513 (2006); http://dx.doi.org/10.1063/1.2187011 (6 pages) | Cited 9 times

Online Publication Date: 27 March 2006

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An approach to precisely determine the magnitude and the sign of Burgers vectors of superscrew dislocations (including elementary screw dislocations and micropipes) in silicon carbide (SiC) single crystals has been developed. The histogram of Burgers vector values associated with micropipes follows Gaussian distribution with most possible absolute Burgers vector value of about 100 Å for both 4H and 6H SiC. Superscrew dislocations are quasistable. Their transformations, such as dissociation, coalescence, and aggregation, follow the principle of Burgers vector conservation and energetically favored behavior. The coalescence of dislocations with same-sign Burgers vectors is less likely to occur during the growth. Finally, a possible mechanism of mismatched coalescence between multiple nucleation sites is proposed to understand the formation of micropipes with large Burgers vectors at the early stage of SiC bulk growth.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Ion-irradiation-induced phase transformation in rare earth sesquioxides (Dy2O3,Er2O3,Lu2O3)

M. Tang, P. Lu, J. A. Valdez, and K. E. Sickafus

J. Appl. Phys. 99, 063514 (2006); http://dx.doi.org/10.1063/1.2184433 (7 pages) | Cited 14 times

Online Publication Date: 27 March 2006

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Polycrystalline pellets of cubic C-type rare earth structure (Iamath) Dy2O3, Er2O3, and Lu2O3 were irradiated at cryogenic temperature (120 K) with 300 keV Kr++ ions to a maximum fluence of 1×1020 Kr/m2. Irradiated specimens were examined using grazing incidence x-ray diffraction and transmission electron microscopy. Ion irradiation leads to different radiation effects in these three materials. First, Dy2O3 begins to transform to a monoclinic B-type rare earth structure (C2/m) at a peak dose of ∼ 5 displacements per atom (dpa), (corresponding to a fluence of 2×1019 Kr/m2). This transformation is nearly complete at a peak dose of 25 dpa (a fluence of 1×1020 Kr/m2). Er2O3 also transforms to the B-type structure, but the transformation starts at a higher irradiation dose of about 15–20 dpa [a fluence of about (6–8)×1019 Kr/m2]. Lu2O3 was found to maintain the C-type structure even at the highest irradiation dose of 25 dpa (a fluence of 1×1020 Kr/m2). No C-to-B transformation was observed in Lu2O3. The irradiation dose dependence of the C-to-B phase transformation observed in Dy2O3, Er2O3, and Lu2O3 is closely related to the temperature dependence of the C-to-B phase transformation found in phase diagrams for these three materials.
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64.70.K- Solid-solid transitions
61.80.Jh Ion radiation effects
61.82.Ms Insulators
81.30.Dz Phase diagrams of other materials

The impact of the density and type of reactive sites on the characteristics of the atomic layer deposited WNxCy films

A. Martin Hoyas, Y. Travaly, J. Schuhmacher, T. Sajavaara, C. M. Whelan, B. Eyckens, O. Richard, S. Giangrandi, B. Brijs, W. Vandervorst, K. Maex, J. P. Celis, A. M. Jonas, and A. Vantomme

J. Appl. Phys. 99, 063515 (2006); http://dx.doi.org/10.1063/1.2182074 (8 pages) | Cited 3 times

Online Publication Date: 28 March 2006

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The growth of tungsten nitride carbide (WNxCy) films obtained by atomic layer deposition using triethylboron, tungsten hexafluoride, and ammonia precursors is determined by the density and type of reactive sites. The film properties change as a function of thickness. On silicon dioxide and silicon carbide, growth is initially nonlinear such that the transient regimes are characterized by island formation, as evidenced by a parabolic tungsten growth curve extending to film thicknesses of up to 5 nm. Such films have low densities of ∼ 4–6 g cm−3 corresponding to only ∼ 30%–45% of the bulk density of ∼ 13.1 g cm−3 determined for a WN0.45C0.55 composition. X-ray reflectivity, thermal desorption, and elastic recoil detection spectroscopies reveal surface roughening and compositional and density differences close to the substrate surface. The offset from linear growth in the case of WNxCy films deposited on silicon dioxide is induced by the initial reaction of silanol and siloxane groups with triethylborane resulting in passivating ethylsilyl groups on the surface. A transient regime is not observed for WNxCy growth on hydrogen-terminated silicon with the initial growth being dominated by the reduction of tungsten hexafluoride to tungsten. On silicon nitride a short transient regime is observed relative to the carbide and oxide surfaces attributed to the enhanced binding of the triethylboron precursor.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
66.30.Ny Chemical interdiffusion; diffusion barriers
68.43.Mn Adsorption kinetics

Temperature dependent refractive index of amorphous silicon determined by time-resolved reflectivity during low fluence excimer laser heating

J. D. Hoyland and D. Sands

J. Appl. Phys. 99, 063516 (2006); http://dx.doi.org/10.1063/1.2186378 (4 pages) | Cited 1 time

Online Publication Date: 28 March 2006

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The temperature dependent refractive index of amorphous silicon has been measured at a wavelength of 820 nm from room temperature up to nearly the melting point close to 1200 °C. The method employed is to use a single pulse from a XeCl excimer laser to heat the silicon without crystallizing it and to measure the transient reflectivity. This is then modeled by converting a calculated temperature profile into an effective multilayer structure and calculating the reflectivity using a transfer matrix formulation. The refractive index is optimized using simulated annealing. The real part of the refractive index is found to vary linearly with a temperature coefficient of 3.85×10−4 while the extinction coefficient is found to vary as exp(3.82×10−3T), with T = 0 at room temperature.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Gh Other heat and thermomechanical treatments
42.79.Wc Optical coatings
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