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15 Apr 2001

Volume 89, Issue 8, pp. 4209-4678

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Resonant and nonresonant hyper–Rayleigh scattering of charge-transfer chromophores

C. H. Wang, J. N. Woodford, C. Zhang, and L. R. Dalton

J. Appl. Phys. 89, 4209 (2001); http://dx.doi.org/10.1063/1.1354636 (9 pages) | Cited 13 times

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The first molecular hyperpolarizabilities (β) of a series of charge-transfer nonlinear optical (NLO) chromophores are measured with the hyper-Rayleigh scattering (HRS) technique using two excitation wavelengths at 1064 and 1907 nm. The 1907 nm wavelength is the longest excitation wavelength used for the HRS experiment. For some of these chromophores, β values in excess of 1000×10−30 esu at 1907 nm are obtained, and due to two-photon enhancement, even greater β values are found with the 1064 nm excitation. Chromophores with such large hyperpolarizability are expected to have potential applications in practical electro-optical devices. The dispersion of β is analyzed using a two-vibronic-state model developed previously in our laboratory. The study shows that it is necessary to consider the vibronic structure of the chromophore in the excited state in order to account for the behavior of the first molecular hyperpolarizability of the charge-transfer NLO chromophores. © 2001 American Institute of Physics.
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42.65.Es Stimulated Brillouin and Rayleigh scattering
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.20.Jq Electro-optical effects
42.65.-k Nonlinear optics
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Electrostatic probe diagnostics of a planar-type radio-frequency inductively coupled oxygen plasma

D. C. Seo, T. H. Chung, H. J. Yoon, and G. H. Kim

J. Appl. Phys. 89, 4218 (2001); http://dx.doi.org/10.1063/1.1354633 (6 pages) | Cited 15 times

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An inductively coupled oxygen radio-frequency (13.56 MHz) discharge is investigated based on modeling and experiment. Experimental measurement is done at a range of gas pressure of 1–30 mTorr, and rf power of 100–1000 W. We measure most of the important plasma parameters such as the densities of charged species, electron temperature, plasma potential, and electron energy distribution function. The measured values are compared with the results of the spatially averaged global model. We observe a generally good agreement between the modeling and the experiment. The scaling features, the transition of the operating region, and the radial distributions of charged species are also discussed. © 2001 American Institute of Physics.
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52.70.Ds Electric and magnetic measurements
52.25.Kn Thermodynamics of plasmas
52.80.Pi High-frequency and RF discharges

Influence of beam head effects on high-power klystron amplifier

Han S. Uhm, Hyoung S. Kim, and Gun S. Park

J. Appl. Phys. 89, 4224 (2001); http://dx.doi.org/10.1063/1.1355695 (7 pages) | Cited 1 time

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Transient behavior of the cavity excitation caused by beam head effects in high-power klystrons is investigated. Recognizing that the input cavity in a klystron can be excited by the input microwave signal and the head of the electron beam, it is shown that the frequency of the induced cavity voltage Vs driven by the signal is the same as the signal frequency ωs. On the other hand, the frequency of the induced cavity voltage Vh driven by the beam head is the cavity resonance frequency ω0. An expression of the induced voltage Vh is obtained by making use of the Laplace transformation. The induced voltage Vh caused by the beam head is expressed in terms of the current-change profile in time. The magnitude of the induced voltage caused by the beam head is inversely proportional to the beam rise time, thereby decreasing drastically for a large value of the beam rise time. It is also shown that the beam head effects are completely negligible whenever the beam rise time τr satisfies ω0τr=2nπ where n is an integer. The amplitude of the whole cavity voltage oscillates with the beat wave frequency Δω=ω0−ωs. This amplitude oscillation may play an important role in pulsed high-power klystrons. © 2001 American Institute of Physics.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
84.30.Le Amplifiers
02.30.Uu Integral transforms

Global breakdown in an alternating current plasma display panel

Y. Ikeda, K. Suzuki, H. Fukumoto, M. Shibata, M. Ishigaki, J. P. Verboncoeur, P. J. Christenson, and C. K. Birdsall

J. Appl. Phys. 89, 4231 (2001); http://dx.doi.org/10.1063/1.1351058 (9 pages) | Cited 4 times

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In the alternating current plasma display panel, a widespread discharge can take place accidentally in a large number of cells in the upper or lower panel ends. The undesirable discharge is referred to as global breakdown. This is a serious problem, with consequences not only for display quality, but also for product reliability. The mechanism of the global breakdown was examined experimentally using a surface electrometer and theoretically using plasma simulation. From these examinations, the global breakdown mechanism was clarified as follows. Global breakdown was accompanied by charge separation in the horizontal direction of the panel. This charge separation was caused by electron transport downward in the panel during the address discharge. The electron transport formed a negative wall charge on the phosphor surface. When the wall voltage exceeded the insulation voltage of the protective layer, global breakdown occurred. Furthermore, it was clarified that increasing the front dielectric thickness or reducing the back dielectric thickness could suppress the electron transport during the address discharge. These optimizations of cell geometry could eliminate the global breakdown. © 2001 American Institute of Physics.
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52.80.Tn Other gas discharges
52.75.-d Plasma devices
85.60.Pg Display systems
52.25.Fi Transport properties
52.65.Rr Particle-in-cell method
52.65.Pp Monte Carlo methods
52.70.Ds Electric and magnetic measurements

Global model of inductively coupled Ar plasmas using two-temperature approximation

T. Kimura and K. Ohe

J. Appl. Phys. 89, 4240 (2001); http://dx.doi.org/10.1063/1.1354652 (7 pages) | Cited 14 times

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The electron energy distribution function (EEDF) is measured with a Langmuir probe in an inductively coupled rf (13.56 MHz) Ar discharge in the pressure range from 5 to 70 mTorr, by changing the power injected into the plasma up to 100 W. The EEDFs measured at a pressure of 5 mTorr formed a bi-Maxwellian structure, which is not prominent due to high electron density, in the energy region lower than the lowest excitation threshold energy. The EEDF structure in the energy region higher than the threshold has a significant depletion of high energy electrons. The EEDF measured at a pressure higher than 10 mTorr can be approximated using a two-temperature distribution, which consists of the higher temperature in a low-energy region below the lowest excitation threshold and the lower temperature in a high-energy region. A global model using the two-temperature distribution is proposed and compared with the experimental results. The model consists of the rate equations for neutrals and charged particles and an energy-balance equation for electrons together with the balance equation for high-energy electrons. Pressure dependences of the electron density and temperatures predicted in this global model agree well with the experimental results except in the pressure range lower than 10 mTorr. © 2001 American Institute of Physics.
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52.80.Pi High-frequency and RF discharges
52.70.Ds Electric and magnetic measurements
52.25.-b Plasma properties

Characteristic dynamic behavior of dc arc near graphite bar electrodes with short gap

Shin-ichi Tanaka and Toshiro Matsumura

J. Appl. Phys. 89, 4247 (2001); http://dx.doi.org/10.1063/1.1355720 (8 pages) | Cited 3 times

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Periodic sawtooth patterns were observed for arc voltages of dc free burning air arcs between 16 mm diameter graphite bar electrodes with a gap length of 15 mm. Observation with a high-speed video camera showed that the sawtooth wave forms of the arc voltages were brought about by the dynamic motions of the arc spots on the electrodes. The anode spot showed a periodic movement on the electrode edge a few hundreds milliseconds after arc ignition, while no movement of the cathode spot was observed. The deflection of the arc column near the anode spot also showed a characteristic pattern during the periodic movement of the anode spot. In order to investigate the factors influencing the dynamic behavior of the arc column near the anode spot, the Lorentz force applied to the arc column near the anode spot was calculated by taking into account the flux induced by the current distributed inside the anode. It was pointed out that the dynamic behavior of the arc column near the anode spot was interpreted as caused by the Lorentz force. © 2001 American Institute of Physics.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity

Wire vibration, bowing, and breakage in wire electrical discharge machining

C. Arunachalam, M. Aulia, B. Bozkurt, and P. T. Eubank

J. Appl. Phys. 89, 4255 (2001); http://dx.doi.org/10.1063/1.1355281 (8 pages) | Cited 2 times

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This article provides an analysis of the wire electrical discharge machining (EDM) process. The causes of wire vibration, bowing, and breakage are identified. The cross sectional configuration of an eroded wire is derived from basic physics under the assumption that the erosion rate is constant. This configuration is verified experimentally with further explanation as to why numerous experimental studies have yielded different configurations. A computational model has been developed that can evaluate the systematic effects that lead to wire breakage by determining the stress induced by wire erosion and the stress induced by the sparks during the operation of a wire-cutting EDM machine. This model is also capable of determining the extent of wire bowing and vibrations in these machines but only in the frontal direction. The model is supported by data from experiments performed on an AGIECUT 612 wire machine cutting a 10 mm high copper bar with a 0.15 mm brass wire to acquire wire breakage data. The nearly parabolic shape of the bowed wire agrees with the results of other authors making more restrictive assumptions. © 2001 American Institute of Physics.
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81.20.Wk Machining, milling
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
81.05.Bx Metals, semimetals, and alloys
06.60.Vz Workshop procedures (welding, machining, lubrication, bearings, etc.)
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
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Recombination enhanced defect reactions in 1 MeV electron irradiated p InGaP

Aurangzeb Khan, Masafumi Yamaguchi, Jacques C. Bourgoin, Koshi Ando, and Tatsuya Takamoto

J. Appl. Phys. 89, 4263 (2001); http://dx.doi.org/10.1063/1.1353806 (6 pages) | Cited 11 times

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Direct recombination enhanced annealing of the radiation-induced defect H2 in p InGaP has been observed by deep level transient spectroscopy (DLTS). Detailed analysis of the annealing data at zero and reverse bias shows that annealing rates are independent of the defect charge state or this defect interacts with the two bands, i.e., is a recombination center trapping alternatively an electron, then a hole. An experiment based on minority carrier capture on a majority trap by the double carrier pulse DLTS technique further supports the evidence that H2 has a large minority carrier capture cross section and is an efficient nonradiative recombination center. Recombination-enhanced defect annealing rates obeys a simple Arrhenius law with an activation enthalpy of 0.51±0.09 eV, in contrast to athermal processes observed in GaP. Detailed analysis of results reveals that the mechanism involved in the minority carrier injection annealing of the H2 defect is energy release mechanism in which enhancement is induced by the energy which is released when a minority carrier is trapped on the defect site. Finally, analysis of the depth profiles data relates that H2 acts as a donor, which partially compensates the acceptors. © 2001 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.82.Fk Semiconductors
61.80.Fe Electron and positron radiation effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Cc Kinetics of defect formation and annealing

Copper gettering by aluminum precipitates in aluminum-implanted silicon

G. A. Petersen and S. M. Myers

J. Appl. Phys. 89, 4269 (2001); http://dx.doi.org/10.1063/1.1353557 (6 pages) | Cited 3 times

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Copper in Si is shown to be strongly gettered by Al-rich precipitates formed by implanting Al to supersaturation and then annealing. At temperatures ranging from 600 to 800 °C a layer containing Al precipitates is found to getter Cu from Cu silicide located on the opposite side of a 0.25 mm Si wafer, indicating a substantially lower chemical potential for the Cu in the molten-Al phase. Cu gettering proceeds rapidly until an atomic ratio of approximately 2 Cu atoms to 1 Al atom is reached in the precipitated Al region, after which the gettering process slows down. Redistribution of Cu from one Al-rich layer to another at low Cu concentrations demonstrates that a segregation-type gettering mechanism is operating. Cu gettering occurs primarily in the region containing the precipitated Al rather than in the region where the Al is entirely substitutional. © 2001 American Institute of Physics.
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61.72.Yx Interaction between different crystal defects; gettering effect
81.05.Cy Elemental semiconductors
81.65.Tx Gettering
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation

Computer simulation of disordering and amorphization by Si and Au recoils in 3C–SiC

F. Gao and W. J. Weber

J. Appl. Phys. 89, 4275 (2001); http://dx.doi.org/10.1063/1.1355717 (7 pages) | Cited 32 times

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Molecular dynamics has been employed to study the disordering and amorphization processes in SiC irradiated with Si and Au ions. The large disordered domains, consisting of interstitials and antisite defects, are created in the cascades produced by Au primary knock-on atoms (PKAs); whereas Si PKAs generate only small interstitial clusters, with most defects being single interstitials and vacancies distributed over a large region. No evidence of amorphization is found at the end of the cascades created by Si recoils. However, the structure analysis indicates that the large disordered domains generated by Au recoils can be defined as an amorphous cluster lacking long-range order. The driving force for amorphization in this material is due to the local accumulation of Frenkel pairs and antisite defects. These results are in good agreement with experimental evidence, i.e., the observed higher disordering rate and the residual disorder after annealing for irradiation with Au2+ are associated with a higher probability for the in-cascade amorphization or formation of a large disordered cluster. © 2001 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
81.05.Gc Amorphous semiconductors
02.70.Ns Molecular dynamics and particle methods
61.43.Bn Structural modeling: serial-addition models, computer simulation
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing

Nanometer-scale metal precipitates in multicrystalline silicon solar cells

Scott A. McHugo, A. C. Thompson, A. Mohammed, G. Lamble, I. Périchaud, S. Martinuzzi, M. Werner, M. Rinio, W. Koch, H.-U. Hoefs, and C. Haessler

J. Appl. Phys. 89, 4282 (2001); http://dx.doi.org/10.1063/1.1330552 (7 pages) | Cited 31 times

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In this study, we have utilized characterization methods to identify the nature of metal impurity precipitates in low performance regions of multicrystalline silicon solar cells. Specifically, we have utilized synchrotron-based x-ray fluorescence and x-ray absorption spectromicroscopy to study the elemental and chemical nature of these impurity precipitates, respectively. We have detected nanometer-scale precipitates of Fe, Cr, Ni, Cu, and Au in multicrystalline silicon materials from a variety of solar cell manufacturers. Additionally, we have obtained a direct correlation between the impurity precipitates and regions of low light-induced current, providing direct proof that metal impurities play a significant role in the performance of multicrystalline silicon solar cells. Furthermore, we have identified the chemical state of iron precipitates in the low-performance regions. These results indicate that the iron precipitates are in the form of oxide or silicate compound. These compounds are highly stable and cannot be removed with standard silicon processing, indicating remediation efforts via impurity removal need to be improved. Future improvements to multicrystalline silicon solar cell performance can be best obtained by inhibiting oxygen and metal impurity introduction as well as modifying thermal treatments during crystal growth to avoid oxide or silicate formation © 2001 American Institute of Physics.
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84.60.Jt Photoelectric conversion
81.05.Cy Elemental semiconductors
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
78.70.Dm X-ray absorption spectra
61.72.S- Impurities in crystals
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation

Shallow thermal donors in nitrogen-doped silicon

V. V. Voronkov, M. Porrini, P. Collareta, M. G. Pretto, R. Scala, R. Falster, G. I. Voronkova, A. V. Batunina, V. N. Golovina, L. V. Arapkina, A. S. Guliaeva, and M. G. Milvidski

J. Appl. Phys. 89, 4289 (2001); http://dx.doi.org/10.1063/1.1356436 (5 pages) | Cited 19 times

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Silicon crystals doped with nitrogen from the melt contain shallow thermal donors (STDs) detected both optically and electrically. Annealing samples at 600 and 650 °C results in a saturated STD concentration that depends on the nitrogen concentration approximately by a square-root law. This indicates the involvement of only one nitrogen atom in every STD species. The model of STDs consistent with the present data is the NOm complex of a nitrogen interstitial and m oxygen atoms; the concentration of every STD species reaches the equilibrium value during annealing. The temperature dependence of the equilibrium reaction constant allows us to estimate the average number of oxygen atoms m of the STD complexes as 3. © 2001 American Institute of Physics.
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71.55.Cn Elemental semiconductors
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
61.72.J- Point defects and defect clusters

Elastic properties, intrinsic and photoinduced stress in hydrogenated amorphous-silicon thin films with different hydrogen content

E. Spanakis, E. Stratakis, P. Tzanetakis, and Qi Wang

J. Appl. Phys. 89, 4294 (2001); http://dx.doi.org/10.1063/1.1353807 (7 pages) | Cited 13 times

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All device-quality hydrogenated amorphous-silicon (a-Si:H) thin films on a substrate exhibit intrinsic compressive stress, induced primarily during growth. Furthermore, it has been established by several previous studies that exposure to intense light at room temperature leads to increase of the compressive stress in addition to the creation of dangling-bond defects, well known as the Staebler–Wronski effect [D. L. Staebler and C. R. Wronski, Appl. Phys. Lett. 31, 292 (1977)]. We present here the results of our investigation of the intrinsic and photoinduced stress as well as the Young’s modulus of a series of samples with different hydrogen content prepared by hot-wire (HW) chemical-vapor deposition. These film properties have been measured with high sensitivity through the bending and flexural oscillation of crystalline silicon microcantilevers upon which we deposited the a-Si:H films. The intrinsic stress decreases with H content in the series. This result complements other investigations linking the saturated defect density to H content in HW samples and validates the generally observed correlation between stress and device performance. The photoinduced stress shows almost an identical initial increase with illumination time in all samples but tends to saturate to a lower value for the lower H concentration. We discuss our results on the variation of the Young’s modulus with H content together with those of a previous study by a different measurement technique and sample growth method and compare both to theoretical calculations. A unified picture emerges clearly suggesting that the microstructure of device quality material is not homogeneous. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
81.05.Gc Amorphous semiconductors
62.20.D- Elasticity
72.40.+w Photoconduction and photovoltaic effects
73.61.Jc Amorphous semiconductors; glasses

Oxygen precipitation in nitrogen-doped Czochralski-grown silicon crystals

Katsuhiko Nakai, Yoshiharu Inoue, Hideki Yokota, Atsushi Ikari, Jun Takahashi, Akiyoshi Tachikawa, Kouichi Kitahara, Yasumitsu Ohta, and Wataru Ohashi

J. Appl. Phys. 89, 4301 (2001); http://dx.doi.org/10.1063/1.1356425 (9 pages) | Cited 51 times

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Oxygen precipitate behavior of nitrogen-doped Czochralski-grown silicon (CZ-Si) crystals is investigated. It is found that nitrogen doping enhances oxygen precipitation after heat treatment. The oxygen precipitate volume density in nitrogen-doped crystals after heat treatment does not change regardless of the heat treatment temperature, while the oxygen precipitate volume density of crystals which are not nitrogen doped decreases as the heat-treatment temperature increases. The characteristics of precipitation behavior in nitrogen-doped CZ-Si crystals are due to the “grown-in” oxygen precipitates, which already exist in an as-grown state with a high volume density. The oxygen precipitation growth of nitrogen-doped crystals is found to be an oxygen diffusion limited process, the same as in the case of the oxygen precipitation growth of crystals which are not nitrogen doped. The formation mechanism of grown-in oxygen precipitates will also be discussed in this article. © 2001 American Institute of Physics.
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81.10.Fq Growth from melts; zone melting and refining
64.75.-g Phase equilibria
61.72.uf Ge and Si
81.05.Cy Elemental semiconductors
81.30.Mh Solid-phase precipitation
81.40.Gh Other heat and thermomechanical treatments
66.30.J- Diffusion of impurities

Photoluminescence and structural studies on extended defect evolution during high-temperature processing of ion-implanted epitaxial silicon

P. K. Giri, S. Coffa, V. Raineri, V. Privitera, G. Galvagno, A. La Ferla, and E. Rimini

J. Appl. Phys. 89, 4310 (2001); http://dx.doi.org/10.1063/1.1357464 (8 pages) | Cited 4 times

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Low-temperature photoluminescence (PL) spectroscopy, in conjunction with transmission electron microscopy (TEM) and optical microscopy (OM) have been carried out to investigate the origin of radiative recombination from various extended defects that evolve during high-temperature processing of ion-implanted epitaxial silicon. From PL studies on N2-annealed samples, we provide spectroscopic evidence of precipitation of the implanted impurities well below the solid-solubility limit. This result is being supported by observations from secondary ion mass spectrometry and spreading resistance profiling of the implanted ions. Cross sectional TEM analyses on these samples reveal 〈111〉-oriented precipitates located in a region containing a high dislocation density. Postimplantation annealing in oxygen ambient results in the formation of dislocations and oxidation-induced stacking faults (OISF). A systematic analysis of PL spectra on different-implanted and preannealed samples, in conjunction with TEM and OM analyses, reveals that the conventionally observed dislocation-related D1 and D2 lines in the PL spectrum is not a characteristic of the OISF, but of the dislocations only. It is shown that the OISF acts as a nonradiative channel for luminescence in silicon. Various other sources of nonradiative channels in silicon are also presented and the efficacy of photoluminescence technique in the characterization of process-induced defects in silicon is discussed. © 2001 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.uf Ge and Si
61.72.Nn Stacking faults and other planar or extended defects
68.37.Lp Transmission electron microscopy (TEM)
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Optical alignment of liquid crystals

D. Dantsker, J. Kumar, and S. K. Tripathy

J. Appl. Phys. 89, 4318 (2001); http://dx.doi.org/10.1063/1.1353811 (8 pages) | Cited 16 times

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An optical method is described for the preparation of a liquid crystal cell. In one, single exposure step a surface relief grating is generated in a photopolymer layer deposited on a glass substrate. Such substrates then orient liquid crystals in contact with them and homogeneous alignment results. An analysis of the nematic liquid crystal orientation in terms of nematic liquid crystal cell parameters as encountered in applications has been made. Consideration of the different mechanisms proposed to explain the origin of liquid crystal alignment and of the conditions required for the generation of surface relief grating in a photopolymer layer has led to the conclusion that both the photoinduced chromophore theory and the surface oriented polymer chains theory are unable to explain the alignment mechanism. On the other hand, the elastic strain energy theory, which is based on geometrical factors, agrees with the observed spatial molecular orientation of the liquid crystals. © 2001 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
78.20.Jq Electro-optical effects

Threading dislocation evolution in mega-electron-volt phosphorus implanted silicon

Craig Jasper, Suman K. Banerjee, Allen Hoover, and Kevin S. Jones

J. Appl. Phys. 89, 4326 (2001); http://dx.doi.org/10.1063/1.1351865 (6 pages) | Cited 1 time

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The effect of dose and energy on postannealing defect formation for high energy (mega-electron-volt) phosphorus implanted silicon has been studied using etch pit studies and transmission electron microscopy (TEM). Previous work has shown that after annealing there is a strong dependence of dislocation density threading to the surface on the implanted phosphorus dose and energy. A superlinear increase in threading dislocation density (TDD) with implant energy between 180 and 1500 keV is observed for a dose of 1×1014 cm−2. In addition as a function of ion fluence, there is a maximum in the threading dislocation density at a dose of 1×1014 cm−2 followed by a rapid decrease in TDD. Both the superlinear increase in TDD with increasing energy and the rapid decrease with increasing dose have been further investigated by TEM. A TEM study of these higher doses revealed formation of a strong bimodal loop distribution with small loops averaging <1000 Å and large loops averaging around 1 μm in size. Over the dose range of 1×1014 cm−2 to 5×1014 cm−2, the superlinear decrease in TDD from 1×106 cm−2 to <1×104 cm−2 coincides with the superlinear increase in small dislocation loops from below 1×106 cm−2 to above 1×1010 cm−2. It is suggested that the homogeneous nucleation theory can explain many of the results. However, the chemical presence of phosphorus appears to also play an important role in the formation of the small dislocation loops and possibly threading dislocations. © 2001 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Lk Linear defects: dislocations, disclinations
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments

Electromigration in eutectic SnPb solder lines

Q. T. Huynh, C. Y. Liu, Chih Chen, and K. N. Tu

J. Appl. Phys. 89, 4332 (2001); http://dx.doi.org/10.1063/1.1357459 (4 pages) | Cited 42 times

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We have prepared eutectic SnPb solder lines for electromigration study by a process of solder reflow into V-grooves etched on (001) Si wafer surfaces. They are thick lines and are highly reproducible. We report here results of lines of 100 μm in width and 150 to 800 μm in length, stressed by a current density of 2.8×104 A/cm2 at 150 °C in ambient. The accumulation of a large lump of solder, rather than hillocks of Sn and Pb, was observed at the anode, and depletions and voids were observed at the cathode. By measuring the volume of the lump, we have calculated the average effective charge number of electromigration in the eutectic solder to be 33, which is close to the reported value of 47 for self-electromigration in bulk Pb. Using x-ray dispersive analysis, we found that Pb is the dominant diffusing species. © 2001 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration
61.72.Qq Microscopic defects (voids, inclusions, etc.)
68.35.Fx Diffusion; interface formation

Growth and characterization of a novel In2Se3 structure

C. H. de Groot and J. S. Moodera

J. Appl. Phys. 89, 4336 (2001); http://dx.doi.org/10.1063/1.1355287 (5 pages) | Cited 27 times

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Thin films of In2Se3 deposited by thermal co-evaporation crystallize upon vacuum annealing almost single phase into an, up to now, unknown structure. Only when the films are capped with a thin oxide layer before annealing, the reportedly stable γ-In2Se3 structure, single phase and aligned along the c axis forms. Rutherford backscattering confirms an In to Se ratio of 2 to 3 for both structures. Nevertheless, the new structure has distinct x-ray diffraction peaks and Raman spectra. The new structure has a much lower resistivity than the γ-In2Se3 structure, consistent with its smaller electrical and optical energy gap. Both structures show large photoconductivity. © 2001 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
72.80.Jc Other crystalline inorganic semiconductors
68.55.A- Nucleation and growth
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
61.72.Cc Kinetics of defect formation and annealing
78.30.Hv Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
78.66.Li Other semiconductors

Structural study of InGaAs/GaAs quantum dots grown by metalorganic chemical vapor deposition for optoelectronic applications at 1.3 μm

A. Passaseo, R. Rinaldi, M. Longo, S. Antonaci, A. L. Convertino, R. Cingolani, A. Taurino, and M. Catalano

J. Appl. Phys. 89, 4341 (2001); http://dx.doi.org/10.1063/1.1351861 (8 pages) | Cited 21 times

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We have studied the influence of difference growth conditions on the two-dimensional to three-dimensional growth mode transition for a specific class of InGaAs/GaAs quantum dots (QDs) optimized for applications to optical devices operating around 1.3 μm (In content x≈0.5). The dots are grown by low-pressure metalorganic chemical vapor deposition on GaAs substrates. We demonstrate that the critical layer thickness corresponding to optimized single-QD layer structures (i.e., with reduced wetting layer thickness and high uniformity) can be controlled by kinetic effects. The optimized growth conditions allow us to grow six-layers stacked QD structures as active material for the fabrication of a light emitting devices operating around 1.3 μm at room temperature. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.15.Kk Vapor phase epitaxy; growth from vapor phase
85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Elastic properties of nanocrystalline zirconium–silicon–boron thin films

M. Chirita, H. Xia, R. Sooryakumar, J. B. Tolle, V. M. Torres, B. J. Wilkens, D. J. Smith, J. Kouvetakis, and I. S. T. Tsong

J. Appl. Phys. 89, 4349 (2001); http://dx.doi.org/10.1063/1.1354632 (5 pages) | Cited 3 times

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Thin amorphous films of ZrB3 grown on Si(111) substrates by chemical-vapor deposition are, upon annealing at 960 °C, transformed to films composed of nanocrystallites (6–10 nm extent) with a nominal composition of Zr0.9Si0.3B3. The independent elastic constants of the layers are determined from the dispersion of the surface and pseudo-Sezawa acoustic excitations and reveal large enhancements in the C11 and C44 constants accompanying the conversion of ZrB3 to the nanocrystalline phase. Since the transverse sound velocities of the binary and Zr0.9Si0.3B3 are in near resonance with the sound velocity of Si (VTSi=4.8 km/s), only the Rayleigh surface wave is localized to the film while all higher-order acoustic modes are evanescent. Despite the strong decay channels, high-lying excitations with velocities as large as 25 km/s (≫VTSi) are observed in Brillouin light scattering. Insight into these acoustic properties is provided by evaluating the elastodynamic Green’s functions and associated acoustic-mode densities. © 2001 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
62.20.D- Elasticity
62.65.+k Acoustical properties of solids
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Bz Metals and metallic alloys

Dynamic behavior of thermionic dispenser cathodes under ion bombardment

R. Cortenraad, A. W. Denier van der Gon, H. H. Brongersma, G. Gärtner, D. Raasch, and A. Manenschijn

J. Appl. Phys. 89, 4354 (2001); http://dx.doi.org/10.1063/1.1356433 (11 pages) | Cited 2 times

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We have investigated the surface coverage and electron emission of thermionic dispenser cathodes during 3 keV Ar+ ion bombardment, thereby simulating the bombardment of the cathodes by residual gases that takes place in cathode-ray tubes as used in television sets. During the ion bombardment at the operating temperature of 1030 °C, a dynamic equilibrium is established between the sputter removal and resupply mechanisms of the Ba and O atoms that form the dipole layer on the cathode substrate. We demonstrated that the performance of the cathodes under ion bombardment is governed by the O removal and resupply rates. It was found that the Ba resupply rate is almost an order of magnitude higher than the O resupply rate, but that the Ba can only be present on the surface bound to O atoms. Therefore, the Ba/O ratio is approximately equal to unity during the ion bombardment. Based on the investigations of the removal and resupply processes, we proposed a model that accurately describes the surface coverage and electron emission during the ion bombardment, including the dependence of the ion flux and cathode temperature. © 2001 American Institute of Physics.
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84.47.+w Vacuum tubes

Optoelectronic device performance on reduced threading dislocation density GaAs/Si

P. J. Taylor, W. A. Jesser, J. D. Benson, M. Martinka, J. H. Dinan, J. Bradshaw, M. Lara-Taysing, R. P. Leavitt, G. Simonis, W. Chang, W. W. Clark, and K. A. Bertness

J. Appl. Phys. 89, 4365 (2001); http://dx.doi.org/10.1063/1.1347000 (11 pages) | Cited 13 times

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A technique for the heteroepitaxy of GaAs/Si films having reduced threading dislocation density is presented. The important attribute of this technique is the suppression of three-dimensional Volmer–Weber island formation during initial deposition. This suppression is achieved by deposition of a stoichiometric GaAs buffer layer by a migration-enhanced epitaxy technique on silicon at 348 K to a thickness greater than the “monolithic thickness,” hm. Subsequent GaAs films deposited by conventional molecular beam epitaxy on buffer layers of thickness greater than hm possess structural and optical characteristics that exceed those for state-of-the-art GaAs/Si layers: an x-ray full width at half maximum (FWHM) of 110 arcsec with a dislocation density at the film surface of 3×106 cm−2 and a concomitant 4 K photoluminescence FWHM of 2.1 meV. The p-i-n structures suitable for use as light-emitting diodes (LEDs) that were grown on the reduced threading dislocation density GaAs/Si and by means of forward- and reverse-bias measurements, demonstrated an ideality factor of n=1.5, an increased reverse-bias breakdown electric field of 2.1×107 V/m, and an intrinsic region resistivity of 4×107 Ω cm for LEDs of increasingly smaller mesa size. © 2001 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
81.05.Cy Elemental semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
85.60.Jb Light-emitting devices
85.60.Dw Photodiodes; phototransistors; photoresistors

Energy dependence of electronic energy relaxation in poly(p-phenylenevinylene)

M. W. McCutcheon, Jeff F. Young, A. G. Pattantyus-Abraham, and M. O. Wolf

J. Appl. Phys. 89, 4376 (2001); http://dx.doi.org/10.1063/1.1353555 (4 pages) | Cited 2 times

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Femtosecond time-resolved photoluminescence spectroscopy is used to study the dynamics of optical emission from poly(p-phenylenevinylene) at 77 K over an energy range of 2.19–2.37 eV. All of the decay curves in this energy range can be described by the summation of two exponential functions. Analysis of the spectral dependence of the time constants extracted from these fits indicates that the transient photoluminescence at any given wavelength is due in general to the superposition of three transitions emanating from a single set of inhomogeneously broadened excitons. The three distinct transitions correspond to processes in which two, one, or zero phonons are excited in the host polymer during the emission event. By separating out these three contributions, it is determined that the effective lifetime of the inhomogeneously broadened excitons increases monotonically from 980 fs at 280 meV above the peak in the density of states (DOS), to 114 ps near the peak in the DOS. © 2001 American Institute of Physics.
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78.55.Kz Solid organic materials
42.70.Jk Polymers and organics
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.47.-p Spectroscopy of solid state dynamics

Giant Faraday rotation of blue light in epitaxial CexY3−xFe5O12 films grown by pulsed laser deposition

Hyonju Kim, Alex Grishin, and K. V. Rao

J. Appl. Phys. 89, 4380 (2001); http://dx.doi.org/10.1063/1.1357463 (4 pages) | Cited 5 times

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We report crystalline, magnetic, and magneto-optic (MO) properties of Ce-substituted yttrium iron garnet (CexY3−xFe5O12) thin films epitaxially grown onto single crystal Gd3Ga5O12 (111) substrates using Nd:YAG pulsed laser deposition technique. Oxygen ambient pressure used for the growth is found to be the critical parameter to prepare CexY3−xFe5O12 films with good crystalline and magnetic properties as well as large MO effect. The film fabricated at 50 m Torr oxygen pressure exhibits a maximum Faraday rotation (FR) θF=1.78 and 4°/μm at λ=633 and 430 nm, respectively, a minimum in-plane coercivity Hc=35 Oe, and the narrowest full width at half maximum = 0.06° for the (444) x-ray Bragg reflection rocking curve. The analog of the Verdet constant V=θF/4πMs also found to be dependent on the oxygen ambient pressure reaches a value as high as 1.41°/μm kG at 633 nm, suggesting that this material is useful for MO applications. The energy dispersion FR spectra, measured over visible region 400 to 840 nm, clearly demonstrate that Ce substitution prominently enhances Faraday effect at 690 and at 430 nm blue-wavelength region. © 2001 American Institute of Physics.
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78.20.Ls Magneto-optical effects
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.40.Ha Other nonmetallic inorganics
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