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15 Jun 2010

Volume 107, Issue 12, Articles (12xxxx)

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J. Appl. Phys. 107, 121301 (2010); http://dx.doi.org/10.1063/1.3386412 (47 pages)

D. T. J. Hurle
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A thermodynamic analysis of native point defect and dopant solubilities in zinc-blende III–V semiconductors

D. T. J. Hurle

J. Appl. Phys. 107, 121301 (2010); http://dx.doi.org/10.1063/1.3386412 (47 pages) | Cited 2 times

Online Publication Date: 21 June 2010

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A thermodynamic model is used to analyze available experimental data relevant to point defects in the binary zinc-blende III–V compounds (Ga,In)-(P,As,Sb). The important point defects and their complexes in each of the materials are identified and included in the model. Essentially all of the available experimental data on dopant solubility, crystal density, and lattice parameter of melt and solution grown crystals and epilayers are reproduced by the model. It extends an earlier study [ Hurle, J. Appl. Phys. 85, 6957 (1999) ] devoted solely to GaAs. Values for the enthalpy and entropy of formation of both native and dopant related point defects are obtained by fitting to experimental data. In undoped material, vacancies, and interstitials on the Group V sublattice dominate in the vicinity of the melting point (MP) in both the phosphides and arsenides, whereas, in the antimonides, vacancies on both sublattices dominate. The calculated concentrations of the native point defects are used to construct the solidus curves of all the compounds. The charged native point defect concentrations at the MP in four of the six materials are significantly higher than their intrinsic carrier concentrations. Thus the usually assumed high temperature “intrinsic” electroneutrality condition for undoped material (n = p) is not valid for these materials. In GaSb, the GaSb antisite defect appears to be grown-in from the melt. This contrasts with the AsGa defect in GaAs for which the concentration grown-in at the MP is negligibly small. Compensation of donor-doped material by donor-Group III vacancy complexes is shown to exist in all the compounds except InP where Group VI doped crystals are uncompensated and in InSb where there is a lack of experimental data. The annealing effects in n+ GaAs, including lattice superdilation, which were shown in the earlier paper to be due to Group III vacancy undersaturation during cooling, are found to be present also in GaSb and InAs. Results for native point defects are compared with reported “first principles” calculations for GaAs. It is seen that, while there is some accord with experimental findings for low temperature molecular beam epitaxial (MBE) growth, they fail totally to predict the behavior under high temperature growth conditions. The analysis of data on liquid phase epitaxy (LPE) growth of GaAs from Bi solution in the earlier paper has been re-calculated in the light of experimental data that showed that the model used in that paper to represent the Ga–As–Bi phase equilibria was inadequate. An improved model reveals that Ga vacancies exert a greater effect in controlling the extent of the linear range of donor dopant solubility than previously predicted. It has also led to a re-evaluation of the equilibrium EL2 and Ga vacancy concentrations in GaAs during MBE growth under As-rich conditions at low temperatures ( ∼ 500 K). The amended model predicts that the very high concentrations of EL2 and of Ga vacancies observed experimentally are near equilibrium values. The predicted increase in the equilibrium concentrations of these defects at low temperatures results from coulombic attraction between the two defects. At temperatures somewhat lower than 500 K the rate of increase becomes catastrophic.
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81.05.Ea III-V semiconductors
68.55.ag Semiconductors
71.55.Eq III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.55.Gs II-VI semiconductors
61.72.jd Vacancies
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Conformable large-area position-sensitive photodetectors based on luminescence-collecting silicone waveguides

Petr Bartu, Robert Koeppe, Nikita Arnold, Anton Neulinger, Lisa Fallon, and Siegfried Bauer

J. Appl. Phys. 107, 123101 (2010); http://dx.doi.org/10.1063/1.3431394 (6 pages) | Cited 2 times

Online Publication Date: 16 June 2010

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Position sensitive detection schemes based on the lateral photoeffect rely on inorganic semiconductors. Such position sensitive devices (PSDs) are reliable and robust, but preparation with large active areas is expensive and use on curved substrates is impossible. Here we present a novel route for the fabrication of conformable PSDs which allows easy preparation on large areas, and use on curved surfaces. Our device is based on stretchable silicone waveguides with embedded fluorescent dyes, used in conjunction with small silicon photodiodes. Impinging laser light (e.g., from a laser pointer) is absorbed by the dye in the PSD and re-emitted as fluorescence light at a larger wavelength. Due to the isotropic emission from the fluorescent dye molecules, most of the re-emitted light is coupled into the planar silicone waveguide and directed to the edges of the device. Here the light signals are detected via embedded small silicon photodiodes arranged in a regular pattern. Using a mathematical algorithm derived by extensive using of models from global positioning system (GPS) systems and human activity monitoring, the position of light spots is easily calculated. Additionally, the device shows high durability against mechanical stress, when clamped in an uniaxial stretcher and mechanically loaded up to 15% strain. The ease of fabrication, conformability, and durability of the device suggests its use as interface devices and as sensor skin for future robots.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Polarization-tunable chiral nematic liquid crystal lasing

Chun-Ta Wang and Tsung-Hsien Lin

J. Appl. Phys. 107, 123102 (2010); http://dx.doi.org/10.1063/1.3428399 (3 pages) | Cited 1 time

Online Publication Date: 16 June 2010

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A chiral nematic liquid crystal laser with arbitrarily controllable polarization was demonstrated by combining polymeric cholesteric and nematic liquid crystal films. The lasing polarization states can be continuously varied by applying voltages from 1.25 to 2 V. Right-handed circular polarization is switched to left-handed circularly polarization through −45° linearly polarized states. The trajectories of the Stokes parameters on the Poincaré sphere are used to analyze the variation in lasing polarization. The change in polarization is simulated and the simulation agrees closely with the experimental data.
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42.55.-f Lasers
42.79.Kr Display devices, liquid-crystal devices
42.70.Hj Laser materials
42.70.Df Liquid crystals

A study on laser drilling of thin steel sheet in air and underwater

A. K. Nath, D. Hansdah, S. Roy, and A. Roy Choudhury

J. Appl. Phys. 107, 123103 (2010); http://dx.doi.org/10.1063/1.3447866 (9 pages) | Cited 1 time

Online Publication Date: 16 June 2010

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In laser drilling of a thin stainless steel sheet in air with Nd:YAG laser pulses of 0.5–1 ms durations it was observed that the 0.5 ms duration laser pulse was more effective in drilling a through-hole than the relatively longer laser pulses with proportionately more energy. Further, laser drilling could be readily done when the sheet was placed at the focal point of the lens and below it but not above the focal point. On the other hand, the underwater laser drilling could be done when the sheet was placed above the focal point. An attempt has been made to explain these experimental observations considering various processes involved in laser drilling in air and underwater. While the recoil pressure of the vapor and plasma played an important role in laser drilling in air; the radial gradient of recoil pressure of evaporation, the Marangoni force induced by the surface tension gradient in melt pool and the cavitation effect of bubble collapse were believed to be responsible for the material removal in underwater drilling process.
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89.20.Kk Engineering
89.20.Bb Industrial and technological research and development
81.20.Wk Machining, milling
42.62.Cf Industrial applications

Determination of polar anchoring energy of dye-doped liquid crystals by measuring capacitance

Chia-Yi Huang, Zuo-Zhong Cheng, Kuang-Yao Lo, and Chia-Rong Lee

J. Appl. Phys. 107, 123104 (2010); http://dx.doi.org/10.1063/1.3436587 (6 pages)

Online Publication Date: 16 June 2010

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Polar anchoring energy of a dye-doped liquid crystal (DDLC) cell is determined based on capacity measurements. Experimental results indicate that under the illumination of a pump beam, the polar anchoring energy (7.90×10−6 J/m2) includes the adsorption-induced anchoring energy (5.74×10−6 J/m2) and the preexisting-dye-induced anchoring energy (2.16×10−6 J/m2). The latter is attributed to the torque, which is induced by the dye molecules on the boundary surface even before illumination. After the illumination, the adsorption-induced anchoring energy remains and the preexisting-dye-induced anchoring energy disappears, with the former revealing that weak anchoring affects the decay time and threshold voltage of the DDLC cell. Moreover, plotting the polar angle distributions in the DDLC cell reveals its correlation with variations in the capacitance of the DDLC cell.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
68.43.Mn Adsorption kinetics

Valence band effective mass of non-c-plane nitride heterostructures

K. Kojima, M. Funato, Y. Kawakami, and S. Noda

J. Appl. Phys. 107, 123105 (2010); http://dx.doi.org/10.1063/1.3448578 (7 pages) | Cited 4 times

Online Publication Date: 16 June 2010

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Valence band (VB) effective masses of nonpolar and semipolar nitride heterostructures were studied using k⋅p perturbation theory, with a particular focus on band mixing. When the absolute value of the energy separation of the topmost two VBs (|ΔE|) is sufficiently larger than the spin-orbit interaction (Δso), the mixing between these two VBs was negligible. This enabled us to calculate an analytical expression for VB mass expression. Under this condition, the effective mass of the top VB was reduced less than 10% along a certain direction, and less than 25% for an in-plane (x′y′-plane) average, compared to the c-plane case. When ΔE was comparable with Δso, however, the VB structure became isotropic due to band mixing. Consequently, the VB band structure approached that of the c-plane and optical polarization was suppressed. On the other hand, VB mass along the growth direction (z′) was always heavy, similar to that of the c-plane. However, the topmost two VBs had slightly different mass values along z′, which affected radiative properties of non-c-plane nitride quantum wells (less than 2 nm wide) through the difference in quantum confinement strengths.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Nr Semiconductor compounds
73.21.Fg Quantum wells
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Microcavity effect on the nonlinear intersubband response of multiple-quantum-well structures: The strong-coupling-regime

M. Załużny and C. Nalewajko

J. Appl. Phys. 107, 123106 (2010); http://dx.doi.org/10.1063/1.3388344 (8 pages)

Online Publication Date: 16 June 2010

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We theoretically discuss the nonlinear intersubband response of multiple-quantum-well structures embedded in microcavities with plane-wave approximation. We employ a semiclassical approach based on the transfer matrix formalism and the so-called sheet model. The linear absorptive losses are taken into account. It is shown that in the strong-coupling-regime the saturation effect leads to the evolution of the absorption spectra from a pair of simple harmonic oscillators to highly anharmonic ones. The usefulness of the simplified analytical approach, based on a standard multibeam interference analysis and the “mean-field” approximation is also demonstrated.
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78.67.De Quantum wells
42.65.-k Nonlinear optics

Presentation and experimental validation of a model for the effect of thermal annealing on the photoluminescence of self-assembled InAs/GaAs quantum dots

M. Srujan, K. Ghosh, S. Sengupta, and S. Chakrabarti

J. Appl. Phys. 107, 123107 (2010); http://dx.doi.org/10.1063/1.3431388 (7 pages) | Cited 7 times

Online Publication Date: 18 June 2010

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We present a model for the effect of thermal annealing on a single-layer InAs/GaAs quantum dot (QD) heterostructure and study the corresponding variation in full photoluminescence (PL) spectrum. In/Ga interdiffusion due to annealing is modeled by Fickian diffusion and the Schrödinger equation is solved separately for electrons and holes to obtain ground state PL peaks of the heterostructure at different annealing temperatures. We theoretically examine the decrease in strain effects and carrier confinement potentials with annealing. PL spectra of the entire ensemble of QDs, annealed at different temperatures, are calculated from a lognormal distribution of QD heights derived from experimental atomic force microscopy (AFM) data. Results from our calculations, which illustrate the blueshift in emission wavelength and linewidth variation in PL with annealing, are in excellent agreement with experimental PL observations on the same samples. This highlights the potential of the model to assist in precisely engineering the optical properties of QD materials for specific device applications. Moreover, the simplicity of the model and its multiple useful features including computation of material interdiffusion, band profiles and full PL spectra make it a valuable tool to study annealing effects on QD heterostructures.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.37.Ps Atomic force microscopy (AFM)
66.30.Ny Chemical interdiffusion; diffusion barriers
78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)

Heat-driven and electric-field-driven bistable devices using dye-doped nematic liquid crystals

Jin Ki Kim, Khoa Van Le, Surajit Dhara, Fumito Araoka, Ken Ishikawa, and Hideo Takezoe

J. Appl. Phys. 107, 123108 (2010); http://dx.doi.org/10.1063/1.3446826 (4 pages) | Cited 3 times

Online Publication Date: 18 June 2010

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We have demonstrated memory and rewritable bistable devices based on an anchoring transition of a nematic liquid crystal on a perfluoropolymer surface. Spontaneous orientation changes between planar and homeotropic occur on cooling and heating with a large temperature hysteresis. Photo (heat) addressing is possible from homeotropic to planar using dye-doped samples. For a coumarin dye, photoaddressed images are preserved even after heating up the sample to the isotropic temperature, whereas, for a 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran dye the images can be erased by decreasing the temperature out of the thermal hysteresis. Orientation switching also occurs by applying an electric field with a response time of several milliseconds depending on the field strength.
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42.79.Kr Display devices, liquid-crystal devices

Sub-bandgap luminescence centers in silicon created by self-ion implantation and thermal annealing

Yu Yang, Jiming Bao, Chong Wang, and Michael J. Aziz

J. Appl. Phys. 107, 123109 (2010); http://dx.doi.org/10.1063/1.3436572 (5 pages) | Cited 3 times

Online Publication Date: 18 June 2010

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We investigated the conditions for the generation of silicon sub-bandgap luminescence centers (W, R, and D1 centers) in p-type silicon wafer by self-ion implantation and thermal annealing. Luminescence centers and their spatial distributions were probed by measuring their photoluminescence (PL) spectra before and after sequential removal of top surface layers. It was demonstrated that the optimal annealing temperature for W-line is ∼ 300 °C. The strongest R-line is observed in the sample with a dose of 1014 cm−2 and at an annealing temperature of 700 °C. The creation of D1-band requires a minimum dose of 3×1014 cm−2 and a minimum annealing temperature of 800 °C. PL versus etch depth measurements indicate that within the studied dose range, the W-line luminescence centers are distributed beyond twice the ion projected range (Rp ≈ 400 nm), R-line centers are located slightly deeper than the Rp, and D1 related defects are distributed at about the same depth as Rp. These results provide valuable information for fabricating the silicon-based infrared light sources.
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71.20.-b Electron density of states and band structure of crystalline solids
61.80.Jh Ion radiation effects
61.72.U- Doping and impurity implantation
85.40.Ry Impurity doping, diffusion and ion implantation technology
71.20.Mq Elemental semiconductors
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators

Quantum well infrared photodetectors hardiness to the nonideality of the energy band profile

Emmanuel Lhuillier, Nicolas Péré-Laperne, Isabelle Ribet-Mohamed, Emmanuel Rosencher, Gilles Patriarche, Amandine Buffaz, Vincent Berger, Alexandru Nedelcu, and Mathieu Carras

J. Appl. Phys. 107, 123110 (2010); http://dx.doi.org/10.1063/1.3446093 (7 pages) | Cited 1 time

Online Publication Date: 21 June 2010

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We report results on the effect of a nonsharp and disordered potential in quantum well infrared photodetectors (QWIP). Scanning electronic transmission microscopy is used to measure the alloy profile of the structure which is shown to present a gradient of composition along the growth axis. Those measurements are used as inputs to quantify the effect on the detector performance (peak wavelength, spectral broadening, and dark current). The influence of the random positioning of the doping is also studied. Finally we demonstrate that QWIP properties are quite robust with regard to the nonideality of the energy band profile.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Optical evaluation of multichannel radiative transitions originating from 4G5/2 level of Sm3+ in heavy-metal-gallate glasses

J. Zhang, D. L. Yang, E. Y. B. Pun, H. Gong, and H. Lin

J. Appl. Phys. 107, 123111 (2010); http://dx.doi.org/10.1063/1.3448238 (6 pages) | Cited 5 times

Online Publication Date: 21 June 2010

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Conventional visible and novel infrared (IR) emissions of Sm3+ in heavy-metal-gallate glasses (Li2O–K2O–BaO–PbO–Bi2O3–Ga2O3, LKBPBG for short) with low phonon energy have been observed. Judd–Ofelt parameters Ω2 (3.00×10−20 cm2), Ω4 (5.19×10−20 cm2), and Ω6 (1.69×10−20 cm2) indicate a higher asymmetry and stronger covalent environment in the optical glasses. For the visible fluorescence bands peaked at 564, 601, 648, and 710 nm, the maximum stimulated emission cross-sections (σe) were derived to be 1.35×10−22, 9.21×10−22, 9.58×10−22, and 3.91×10−22 cm2, respectively, the values are larger than those in phosphate, oxyfluoroborate, tellurite, and calibo glasses obviously. The observed 1185 nm IR emission lies in the low-loss window of telecommunication system, and the maximum value of σe for this band was obtained to be 6.09×10−23 cm2. The characterization of multichannel radiative transitions of Sm3+ in LKBPBG glasses is beneficial in exposing its potential applications in visible and IR optoelectronic devices.
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42.70.Ce Glasses, quartz
61.43.Fs Glasses
78.60.-b Other luminescence and radiative recombination
81.05.Kf Glasses (including metallic glasses)
78.45.+h Stimulated emission
63.50.Lm Glasses and amorphous solids
78.55.Qr Amorphous materials; glasses and other disordered solids

The effect of rare-earth clustering on charge trapping and electroluminescence in rare-earth implanted metal-oxide-semiconductor light-emitting devices

A. N. Nazarov, S. I. Tiagulskyi, I. P. Tyagulskyy, V. S. Lysenko, L. Rebohle, J. Lehmann, S. Prucnal, M. Voelskow, and W. Skorupa

J. Appl. Phys. 107, 123112 (2010); http://dx.doi.org/10.1063/1.3436591 (14 pages) | Cited 6 times

Online Publication Date: 21 June 2010

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The effect of rare-earth clustering in dielectric media on the electroluminescence (EL) intensity, the charge trapping and the EL quenching was investigated using the example of Tb and Eu-implanted SiO2 layers. It was shown that the increase in the REOX cluster size induced by an increase in the furnace annealing temperature resulted in an increase in the concentration of electron traps with capture cross sections from 2×10−15 to 2×10−18 cm2. This is probably associated with an increase in the concentration of oxygen deficiency centers as well as with strained and dangling bonds in the SiO2 matrix which leads to an enhanced scattering of hot electrons and a decrease in the excitation cross section of the main EL lines of RE3+ ions. For the main EL lines of Tb3+ and Eu3+ ions the relation of the EL quenching to negative and positive charge generation in the SiO2 was considered. It was demonstrated that in case of REOX nanoclusters with small sizes (up to 5 nm) the EL quenching process can mainly be explained by a defect shell model which suggests the formation of negatively charged defect shells around the nanoclusters leading to a Coulomb repulsion of hot electrons and a suppression of the RE3+ excitation. At high levels of the injected charge (more than 2×1020 e/cm2) a second stage of the EL quenching was observed which was contributed to a positive charge accumulation in the SiO2 at a distance beyond the tunneling distance from the SiO2Si interface. In case of Eu-implanted SiO2 the quenching of the main EL line of Eu3+ is mostly correlated with positive charge trapping in the bulk of the dielectric. A model of EL quenching of the main Eu3+ line is proposed.
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85.60.Jb Light-emitting devices
85.30.Tv Field effect devices

High brightness from unstable resonator mid-IR semiconductor lasers

A. P. Ongstad, G. C. Dente, M. L. Tilton, J. R. Chavez, R. Kaspi, and D. M. Gianardi

J. Appl. Phys. 107, 123113 (2010); http://dx.doi.org/10.1063/1.3435208 (4 pages)

Online Publication Date: 22 June 2010

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We compare the performance of several optically pumped unstable resonator semiconductor lasers with cavity lengths of 4, 5, and 6 mm and operating in the mid-IR at 4.7 μm. The unstable resonator lasers (URLs) were fabricated by polishing a diverging cylindrical mirror on one of the facets. In general, the URL beam quality (BQ) was 1–2 times diffraction limited when operated at pump powers below 30 W (URL power ≤ 6 W) As the pump power is increased, the BQ is observed to degrade; at 60 W the URL’s were ∼ 3.5 times diffraction limited (URL power ≈11 W). The highest brightness URL, a 4-mm long device, was compared with an equivalent 4-mm long Fabry–Perot (FP) laser operated at different cavity widths. The performance of the broad area URL (500 μm width), as assessed by power-in-the-bucket measurements, was superior to both wide stripe (500 μm) and narrow pump stripe (100 μm) FP lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Bh Lenses, prisms and mirrors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

A comprehensive analysis of the contributions to the nonlinear optical properties of thin Ag films

Daniel T. Owens, Canek Fuentes-Hernandez, Joel M. Hales, Joseph W. Perry, and Bernard Kippelen

J. Appl. Phys. 107, 123114 (2010); http://dx.doi.org/10.1063/1.3429118 (8 pages) | Cited 10 times

Online Publication Date: 22 June 2010

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The nonlinear optical properties of 20 nm thick Ag films are investigated by time-resolved white- light continuum pump-probe experiments in both transmission and reflection mode. The dynamics of changes in permittivity Δε are measured at wavelengths between 500 to 700 nm. The data is fitted to a modified Drude model in the frequency domain and to a two-temperature model in the time domain. Changes in the individual Drude parameters are calculated as a function of time. A single, coherent model is proposed based on these fittings that describes the dynamics of the nonlinear optical properties of Ag, which could be used to model the nonlinear responses of multilayer structures containing thin films of Ag. The physical origins of the observed responses are discussed.
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78.66.Bz Metals and metallic alloys
78.40.Kc Metals, semimetals, and alloys
77.22.Ch Permittivity (dielectric function)
78.47.jg Time resolved reflection spectroscopy

Magnetic field-induced excitation and optical detection of mechanical modes of microspheres

T. Ioppolo, M. V. Ötügen, and K. Marcis

J. Appl. Phys. 107, 123115 (2010); http://dx.doi.org/10.1063/1.3452363 (4 pages) | Cited 2 times

Online Publication Date: 24 June 2010

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We propose a method to excite and detect the mechanical modes of dielectric microspheres. The mechanical modes are excited by simultaneously imposing static and harmonic magnetic fields on the spheres. They are monitored by simultaneously exciting and tracking the whispering gallery optical modes of the spheres. An analysis is carried out to investigate the relationship between the applied magnetic field and the corresponding whispering gallery mode shifts. Experiments were carried out to demonstrate the proposed magnetic field-induced excitation and optical detection method.
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46.70.-p Application of continuum mechanics to structures

Time resolved studies of catastrophic optical mirror damage in red-emitting laser diodes

Stella N. Elliott, Peter M. Smowton, Mathias Ziegler, Jens W. Tomm, and Ute Zeimer

J. Appl. Phys. 107, 123116 (2010); http://dx.doi.org/10.1063/1.3437395 (7 pages) | Cited 2 times

Online Publication Date: 25 June 2010

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We have observed the changing light intensity during catastrophic optical mirror damage (COMD) on the timescale of tens of nanoseconds using red-emitting AlGaInP quantum well based laser diodes. Using as-cleaved facets and this material system, which is susceptible to COMD, we recorded the drop in light intensity and the area of damage to the facet, as a function of current, for single, high current pulses. We found that in the current range up to 40 A, the total COMD process up to the drop of light intensity to nonlasing levels takes place on a timescale of hundreds of nanoseconds, approaching a limiting value of 200 ns, and that the measured area of facet damage showed a clear increase with drive current. Using a straightforward thermal model, we propose an explanation for the limiting time at high currents and the relationship between the time to COMD and the area of damaged facet material.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Bh Lenses, prisms and mirrors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Left-handed and right-handed one-way edge modes in a gyromagnetic photonic crystal

Cheng He, Xiao-Lin Chen, Ming-Hui Lu, Xue-Feng Li, Wei-Wei Wan, Xiao-Shi Qian, Ruo-Cheng Yin, and Yan-Feng Chen

J. Appl. Phys. 107, 123117 (2010); http://dx.doi.org/10.1063/1.3374470 (5 pages) | Cited 2 times

Online Publication Date: 25 June 2010

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We theoretically reveal that a two-dimensional magneto-optical photonic crystal shows two pairs of one-way edge Dirac cones, whereby only clockwise and anticlockwise circle wave scattering (facing the direction of external applied magnetic field) are allowed in the second and third band-gaps, respectively. These two different chiral pathways originate from the different exchange of Chern numbers, which are attributed to the broken time-reversal symmetry. Moreover, below and above the edge Dirac point, the edge modes show the left-handed (counter propagation of group velocity and phase velocity) and right-handed characters, respectively.
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42.70.Qs Photonic bandgap materials
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.20.Ek Optical activity
78.20.Ls Magneto-optical effects

An exact solution to Maxwell’s equations including an evanescent field for a gapped three layered optical system

Naofumi Kitsunezaki, Jun-ichi Mizusawa, and Akio Kitsunezaki

J. Appl. Phys. 107, 123118 (2010); http://dx.doi.org/10.1063/1.3436613 (9 pages)

Online Publication Date: 28 June 2010

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We have investigated the electromagnetic characteristics of an optical configuration consisting of two dielectric regions of the same n>1 with a thin flat gap of air/vacuum of width d between them. Based on an analytical and exact solution to Maxwell’s equations including an evanescent field in the vacuum gap, we have obtained the transmission property of a four terminal optical circuit that consists of two input lights aimed toward the gap from both sides of the dielectric regions and two output lights from the gap, where all of the four terminals have the same angle to a plane that is vertical to the boundary plane between the dielectric and the vacuum. The results show several unique possible applications of the optical circuit elements such as a variable ratio power splitter, phase to amplitude field modulator, and optical mode selector.
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42.25.Bs Wave propagation, transmission and absorption
42.79.Fm Reflectors, beam splitters, and deflectors
42.79.Hp Optical processors, correlators, and modulators

Design of terahertz detector based on radiation-induced magnetoresistance oscillations

Q. S. Zhou, J. C. Cao, and M. Qi

J. Appl. Phys. 107, 123119 (2010); http://dx.doi.org/10.1063/1.3452387 (4 pages)

Online Publication Date: 28 June 2010

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We have investigated the longitudinal resistivity of two-dimensional (2D) electron gas driven by microwave and magnetic field by using the balance-equation theory. Radiation-induced magnetoresistance oscillations have been reproduced. The period-in-the-inverse-magnetic-field is determined by radiation frequency. This property can be used to design a terahertz detector. The detection is realized by applying a time-varying magnetic field on a 2D electron device and then measuring the difference of longitudinal resistivity with and without radiation. This kind of detector has high sensitivity and high immunity.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
back to top Plasmas and Electrical Discharges

Waves in expanding electronegative plasmas containing double layers

E. Kawamura, A. J. Lichtenberg, and M. A. Lieberman

J. Appl. Phys. 107, 123301 (2010); http://dx.doi.org/10.1063/1.3446291 (9 pages) | Cited 1 time

Online Publication Date: 16 June 2010

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Expanding electronegative (EN) plasmas have been previously observed, experimentally, to generate wave activity. Using a particle-in-cell (PIC) code we have investigated these waves in expanding EN plasmas containing a double layer (DL) between an upstream source region and an expanded downstream region. Oxygen reaction rates were used but modified to correspond more closely to experimental conditions. Under a subset of pressures, for which a DL existed, waves were observed traveling upstream in the expanded region, and growing in amplitude in the direction of travel. Both slow and fast waves were observed. The fast wave existed only over part of the slow wave pressure range. The PIC results were compared to both fluid and kinetic theory, both of which assumed axial uniformity. The results of a somewhat simplified fluid theory, ignoring fast wave coupling and collisions with the background gas, gave a remarkable result: if the theory predicted a slow wave instability for any axial parameters in the downstream region, the instability was observed in the simulation. Conversely, if no instability was predicted at any axial position, no instability was observed. More accurate kinetic calculations, including electron and ion Landau damping, and also collisional damping against the background gas, gave wavelengths and growth rates that were consistent with the PIC simulations, and with the fluid results. The kinetic theory also indicated that the fast waves were always stable but became weakly damped for conditions of unstable slow waves. We postulate that nonlinear and nonuniformity effects excite the fast waves.
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52.40.Kh Plasma sheaths
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.65.-y Plasma simulation

Refractive phenomena in the shock wave dispersion with variable gradients

A. Markhotok and S. Popovic

J. Appl. Phys. 107, 123302 (2010); http://dx.doi.org/10.1063/1.3432565 (4 pages) | Cited 1 time

Online Publication Date: 16 June 2010

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In this article the refraction effects in the weak shock wave (SW) dispersion on an interface with a temperature variation between two mediums are described. In the case of a finite-gradient boundary, the effect of the SW dispersion is remarkably stronger than in the case of a step change in parameters. In the former case the vertical component of velocity for the transmitted SW (the refraction effect) must be taken into account. Results of comparative calculations based on the two-dimensional model corrected for the refraction effect show significant differences in the shapes of the dispersed SW fronts.
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52.35.Tc Shock waves and discontinuities
52.30.-q Plasma dynamics and flow
52.25.Kn Thermodynamics of plasmas
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.40.Hf Plasma-material interactions; boundary layer effects

Measurements of electron energy distribution in tantalum laser-generated plasma

L. Torrisi, D. Mascali, R. Miracoli, S. Gammino, N. Gambino, L. Giuffrida, and D. Margarone

J. Appl. Phys. 107, 123303 (2010); http://dx.doi.org/10.1063/1.3429242 (8 pages) | Cited 4 times

Online Publication Date: 24 June 2010

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The time and space resolved characterization of laser-generated pulsed plasmas is useful not only for the comprehension of basic phenomena involved in the plasma generation and following supersonic expansion, but it also permits to control the nonequilibrium process that is useful for many applications (e.g., ion implantation). The “on-line” characterization can be performed by means of Langmuir probes, ion collectors, and ion energy analyzers, in order to measure the plasma temperatures and densities of atoms, ions, and electrons. The investigated plasmas were generated by means of laser pulses with intensity of the order of 109 W/cm2. The contemporary characterization of the electron (through the Langmuir probe) and ion energy distribution functions, EEDF and IEDF, respectively, permits to correlate the ion properties, like charge states and temperatures, with the electron properties, like the shape of the EEDF at different times and distances from the ablated target surface.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Ds Electric and magnetic measurements
52.25.-b Plasma properties

Properties and etching rates of negative ions in inductively coupled plasmas and dc discharges produced in Ar/SF6

M. Draghici and E. Stamate

J. Appl. Phys. 107, 123304 (2010); http://dx.doi.org/10.1063/1.3452357 (9 pages) | Cited 6 times

Online Publication Date: 24 June 2010

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Negative ion production is investigated in a chamber with transversal magnetic filter operated in dc or inductively coupled plasma (ICP) modes in Ar/SF6 gas mixtures. Plasma parameters are evaluated by mass spectrometry and Langmuir probe for different discharge conditions. The density ratio of negative ion to electron exceeded 300 in dc mode while it was below 100 in the ICP mode. The possibility to apply a large positive bias to an electrode without affecting the plasma potential and the transition from a negative sheath to anodic glow are also investigated. The etching rates by positive and negative ions are evaluated on silicon substrate for different Ar/SF6 gas ratios. The etching rate by negative ions was with less than 5% smaller than that by positive ions.
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52.70.Ds Electric and magnetic measurements
52.80.-s Electric discharges

Measuring D(d,p)T fusion reactant energy spectra with Doppler shifted fusion products

D. R. Boris, G. L. Kulcinski, J. F. Santarius, D. C. Donovan, and G. R. Piefer

J. Appl. Phys. 107, 123305 (2010); http://dx.doi.org/10.1063/1.3437629 (9 pages) | Cited 2 times

Online Publication Date: 25 June 2010

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Deuterium fusion reactant energy spectra have been measured using a diagnostic that records the Doppler shift imparted to charged particle fusion products of the D(d,p)T reaction by the center-of-mass velocity of the deuterium reactants. This diagnostic, known as the fusion ion Doppler shift diagnostic (FIDO) measures fast deuterium energy spectra in the inertial electrostatic confinement (IEC) experiment at the University of Wisconsin–Madison { Santarius et al. [Fusion Sci. Technol. 47, 1238 (2005)] }, a device to confine high energy light ions in a spherically symmetric, electrostatic potential well. This article details the first measurements of the fusion reactant energy spectra in an IEC device as well as the design and principles of operation of the FIDO diagnostic. Scaling of reactant energy spectra with a variety of experimental parameters have been explored.
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25.45.Hi Transfer reactions
27.10.+h A ≤ 5
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