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15 Apr 2012

Volume 111, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 084701 (2012); http://dx.doi.org/10.1063/1.3698319 (11 pages)

Xerxes Lopez-Yglesias, Jason M. Gamba, and Richard C. Flagan
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back to top Lasers, Optics, and Optoelectronics

Light scattering at textured back contacts for n-i-p thin-film silicon solar cells

K. Bittkau, W. Böttler, M. Ermes, V. Smirnov, and F. Finger

J. Appl. Phys. 111, 083101 (2012); http://dx.doi.org/10.1063/1.3703572 (5 pages) | Cited 2 times

Online Publication Date: 16 April 2012

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The angular resolved light scattering at textured back contacts for n-i-p thin-film silicon solar cells is investigated experimentally in air. These results are compared to simulations performed by a scalar model for reflection with excellent agreement. Furthermore, light scattering is modeled for the transmission and reflection inside the silicon solar cell. It is found that the reflection at the back contact dominates the light scattering in the absorber layer. From these simulations, a quantity is derived that successfully predicts the external quantum efficiencies of solar cells on different textures.
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88.40.jj Silicon solar cells

Optically optimal wavelength-scale patterned ITO/ZnO composite coatings for thin film solar cells

Antoine Moreau, Rafik Smaali, Emmanuel Centeno, and Christian Seassal

J. Appl. Phys. 111, 083102 (2012); http://dx.doi.org/10.1063/1.3703670 (6 pages)

Online Publication Date: 17 April 2012

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A methodology is proposed for finding structures that are, optically speaking, locally optimal: a physical analysis of much simpler structures is used to constrain the optimization process. The obtained designs are based on a flat amorphous silicon layer (to minimize recombination) with a patterned anti-reflective coating made of ITO or ZnO, or a composite ITO/ZnO coating. These latter structures are realistic and present good performances despite very thin active layers.
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81.65.-b Surface treatments

Modeling of current gain compression in common emitter mode of a transistor laser above threshold base current

Rikmantra Basu, Bratati Mukhopadhyay, and P. K. Basu

J. Appl. Phys. 111, 083103 (2012); http://dx.doi.org/10.1063/1.4703926 (7 pages)

Online Publication Date: 18 April 2012

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We have obtained the expressions for the terminal currents in a heterojunction bipolar transistor laser the base of which contains a quantum well (QW). The emitter-base junction is assumed to be abrupt, leading to abrupt discontinuity in quasi-Fermi level at the interface. The expressions for the terminal currents as a function of collector-emitter and base-emitter voltages are obtained from the solution of the continuity equation. The current density in the QW located at an arbitrary position in the base is related to the virtual state current density. The threshold current density in the QW is calculated by using the expression for gain obtained from Fermi golden rule. The plot of collector current (IC) versus collector-emitter voltage (VCE) for different values of base current shows the usual transistor characteristics, i.e., a rising portion after a cut-in VCE, and then a saturation behavior. The dc current gain remains constant. However, as the base current exceeds the threshold, a stimulated recombination rate is added to the spontaneous recombination rate and the plots of collector currents become closer for the same increase in base current. This current gain compression is in agreement with the experimental observation. Our calculated values qualitatively agree with other experimental findings; however some features like Early effect do not show up in the calculation.
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85.30.Pq Bipolar transistors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Molecular beam epitaxial growth and characterization of InSb1 − xNx on GaAs for long wavelength infrared applications

Nimai C. Patra, Sudhakar Bharatan, Jia Li, Michael Tilton, and Shanthi Iyer

J. Appl. Phys. 111, 083104 (2012); http://dx.doi.org/10.1063/1.3702453 (8 pages) | Cited 1 time

Online Publication Date: 19 April 2012

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Recent research progress and findings in InSbN have attracted great attention due to its use in long wavelength infrared applications. A large bandgap reduction in InSb resulting from high N incorporation with minimal crystal defects is challenging due to relatively small atomic size of N. Hence optimization of growth conditions plays an important role in the growth of high-quality InSbN epilayers for device purposes. In this paper, we report on the correlation of structural, vibrational, electrical, and optical properties of molecular beam epitaxially grown InSbN epilayers grown on GaAs substrates, as a function of varying growth temperatures. Two dimensional growths of InSb and InSbN were confirmed from dynamic reflection high energy electron diffraction patterns and growth parameters were optimized. High crystalline quality of the epilayers is attested to by a low full width at half maximum of 200 arcsec from high resolution x-ray diffraction (HRXRD) scans and by the high intensity and well-resolved InSb longitudinal optical (LO) and 2nd order InSb LO mode observed from micro-Raman spectroscopy. The N incorporation in these InSbN epilayers is estimated to be 1.4% based on HRXRD simulation. X-ray photoelectron spectroscopy (XPS) studies reveal that most of the N present in the layers are in the form of In-N bonding. Variation of the lattice disorder with growth temperature is correlated with the types of N bonding present, the carrier concentration and mobility, observed in the corresponding XPS spectra and Hall measurements, respectively. XPS analysis, HRXRD scans, and Raman spectral analysis indicate that lower growth temperature favors In-N bonding which dictates N incorporation in the substitutional sites and lattice disorder, whereas, high growth temperature promotes the formation of In-N-Sb bonding. The best room temperature and 77 K electrical transport parameters and maximum redshift in the absorption edge have been achieved in the InSbN epilayer grown in the 290 °C ∼ 330 °C temperature range.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.ag Semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects

Non-equilibrium Green’s function calculation for GaN-based terahertz-quantum cascade laser structures

H. Yasuda, T. Kubis, I. Hosako, and K. Hirakawa

J. Appl. Phys. 111, 083105 (2012); http://dx.doi.org/10.1063/1.4704389 (4 pages) | Cited 1 time

Online Publication Date: 19 April 2012

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We theoretically investigated GaN-based resonant phonon terahertz-quantum cascade laser (QCL) structures for possible high-temperature operation by using the non-equilibrium Green’s function method. It was found that the GaN-based THz-QCL structures do not necessarily have a gain sufficient for lasing, even though the thermal backfilling and the thermally activated phonon scattering are effectively suppressed. The main reason for this is the broadening of the subband levels caused by a very strong interaction between electrons and longitudinal optical (LO) phonons in GaN.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
84.40.-x Radiowave and microwave (including millimeter wave) technology

Cavity suppression in nitride based superluminescent diodes

A. Kafar, S. Stańczyk, S. Grzanka, R. Czernecki, M. Leszczyński, T. Suski, and P. Perlin

J. Appl. Phys. 111, 083106 (2012); http://dx.doi.org/10.1063/1.4704147 (6 pages)

Online Publication Date: 20 April 2012

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We have fabricated two types of InGaN superluminescent diodes applying two different concepts of cavity suppression: a tilted waveguide geometry and passive absorber solution. Both types of devices showed superluminescence behavior, but both eventually lased under the application of high enough current. The lasing threshold turned out to be higher for tilted waveguide devices. By using long (2 mm) waveguides, we managed to demonstrate the power in superluminescent mode exceeding 100 mW in blue/violet part of the spectrum.
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85.60.Jb Light-emitting devices

Homogeneous and elongation-free 3D microfabrication by a femtosecond laser pulse and hologram

M. Yamaji, H. Kawashima, J. Suzuki, S. Tanaka, M. Shimizu, K. Hirao, Y. Shimotsuma, and K. Miura

J. Appl. Phys. 111, 083107 (2012); http://dx.doi.org/10.1063/1.4705286 (7 pages)

Online Publication Date: 23 April 2012

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A new 3D microfabrication method has been developed, which uses only a single femtosecond laser pulse and a hologram. For the microfabrication inside transparent materials, the optical axial elongation of the fabricated structure is a major problem that has thus far limited design flexibility, especially for the direction along the optical axis. By controlling the light intensity distribution profile and using the adequate focal length of the hologram, this problem was solved and homogeneous and elongation-free 3D microfabrication was achieved.
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81.16.-c Methods of micro- and nanofabrication and processing
42.62.-b Laser applications
42.40.Kw Holographic interferometry; other holographic techniques
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

A scattering model for nano-textured interfaces and its application in opto-electrical simulations of thin-film silicon solar cells

K. Jäger, M. Fischer, R. A. C. M. M. van Swaaij, and M. Zeman

J. Appl. Phys. 111, 083108 (2012); http://dx.doi.org/10.1063/1.4704372 (9 pages) | Cited 4 times

Online Publication Date: 23 April 2012

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We present a scattering model based on the scalar scattering theory that allows estimating far field scattering properties in both transmission and reflection for nano-textured interfaces. We first discuss the theoretical formulation of the scattering model and validate it for nano-textures with different morphologies. Second, we combine the scattering model with the opto-electric asa simulation software and evaluate this combination by simulating and measuring the external parameters and the external quantum efficiency of solar cells with different interface morphologies. This validation shows that the scattering model is able to predict the influence of nano-textured interfaces on the solar cell performance. The scattering model presented in this manuscript can support designing nano-textured interfaces with optimized morphologies.
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68.35.Ct Interface structure and roughness
88.40.jj Silicon solar cells

Raman scattering and anti-Stokes luminescence in poly-paraphenylene vinylene/carbon nanotubes composites

M. Baibarac, F. Massuyeau, J. Wery, I. Baltog, and S. Lefrant

J. Appl. Phys. 111, 083109 (2012); http://dx.doi.org/10.1063/1.4705403 (5 pages)

Online Publication Date: 27 April 2012

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In this paper, we present Raman scattering and luminescence of poly-paraphenylene vinylene/single-walled carbon nanotubes composites, focused on data recorded in the anti-Stokes branch. We demonstrate that, when the excitation energy is in the long wavelength tail of the fundamental absorption edge, an anti-Stokes signal is generated, whose origin is a photon absorption accompanied by a phonon process from lower to upper vibronic states. The efficiency of this anti-Stokes photo-luminescence is increased when composites films are deposited onto an Au rough surface acting as a surface enhanced Raman scattering substrate. This mechanism is explained by a coherent anti-Stokes Raman scattering-like process, as observed in other nano-structured materials.
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78.66.Sq Composite materials
81.07.Pr Organic-inorganic hybrid nanostructures
81.16.-c Methods of micro- and nanofabrication and processing
78.30.-j Infrared and Raman spectra
78.55.-m Photoluminescence, properties and materials
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
back to top Plasmas and Electrical Discharges

Breakdown voltage reliability improvement in gas-discharge tube surge protectors employing graphite field emitters

Marko Žumer, Bojan Zajec, Robert Rozman, and Vincenc Nemanič

J. Appl. Phys. 111, 083301 (2012); http://dx.doi.org/10.1063/1.4704699 (6 pages)

Online Publication Date: 19 April 2012

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Gas-discharge tube (GDT) surge protectors are known for many decades as passive units used in low-voltage telecom networks for protection of electrical components from transient over-voltages (discharging) such as lightning. Unreliability of the mean turn-on DC breakdown voltage and the run-to-run variability has been overcome successfully in the past by adding, for example, a radioactive source inside the tube. Radioisotopes provide a constant low level of free electrons, which trigger the breakdown. In the last decades, any concept using environmentally harmful compounds is not acceptable anymore and new solutions were searched. In our application, a cold field electron emitter source is used as the trigger for the gas discharge but with no activating compound on the two main electrodes. The patent literature describes in details the implementation of the so-called trigger wires (auxiliary electrodes) made of graphite, placed in between the two main electrodes, but no physical explanation has been given yet. We present experimental results, which show that stable cold field electron emission current in the high vacuum range originating from the nano-structured edge of the graphite layer is well correlated to the stable breakdown voltage of the GDT surge protector filled with a mixture of clean gases.
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84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
79.70.+q Field emission, ionization, evaporation, and desorption
84.47.+w Vacuum tubes

Plasma potential mapping of high power impulse magnetron sputtering discharges

Albert Rauch, Rueben J. Mendelsberg, Jason M. Sanders, and André Anders

J. Appl. Phys. 111, 083302 (2012); http://dx.doi.org/10.1063/1.3700242 (12 pages) | Cited 4 times

Online Publication Date: 23 April 2012

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multimedia

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Pulsed emissive probe techniques have been used to determine the plasma potential distribution of high power impulse magnetron sputtering (HiPIMS) discharges. An unbalanced magnetron with a niobium target in argon was investigated for a pulse length of 100 μs at a pulse repetition rate of 100 Hz, giving a peak current of 170 A. The probe data were recorded with a time resolution of 20 ns and a spatial resolution of 1 mm. It is shown that the local plasma potential varies greatly in space and time. The lowest potential was found over the target’s racetrack, gradually reaching anode potential (ground) several centimeters away from the target. The magnetic presheath exhibits a funnel-shaped plasma potential resulting in an electric field which accelerates ions toward the racetrack. In certain regions and times, the potential exhibits weak local maxima which allow for ion acceleration to the substrate. Knowledge of the local E and static B fields lets us derive the electrons’ E×B drift velocity, which is about 105 m/s and shows structures in space and time.
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52.80.Pi High-frequency and RF discharges
52.40.Kh Plasma sheaths
52.70.Ds Electric and magnetic measurements

High electronegativity multi-dipolar electron cyclotron resonance plasma source for etching by negative ions

E. Stamate and M. Draghici

J. Appl. Phys. 111, 083303 (2012); http://dx.doi.org/10.1063/1.4704696 (6 pages) | Cited 1 time

Online Publication Date: 23 April 2012

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A large area plasma source based on 12 multi-dipolar ECR plasma cells arranged in a 3 × 4 matrix configuration was built and optimized for silicon etching by negative ions. The density ratio of negative ions to electrons has exceeded 300 in Ar/SF6 gas mixture when a magnetic filter was used to reduce the electron temperature to about 1.2 eV. Mass spectrometry and electrostatic probe were used for plasma diagnostics. The new source is free of density jumps and instabilities and shows a very good stability for plasma potential, and the dominant negative ion species is F−. The magnetic field in plasma volume is negligible and there is no contamination by filaments. The etching rate by negative ions measured in Ar/SF6/O2 mixtures was almost similar with that by positive ions reaching 700 nm/min.
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52.77.Bn Etching and cleaning
52.70.Nc Particle measurements
81.65.Cf Surface cleaning, etching, patterning
52.70.Ds Electric and magnetic measurements
52.50.Dg Plasma sources

rf-power and the ring-mode to red-mode transition in an inductively coupled plasma

J. G. Coffer and J. C. Camparo

J. Appl. Phys. 111, 083304 (2012); http://dx.doi.org/10.1063/1.4705469 (7 pages)

Online Publication Date: 25 April 2012

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The optical output of an alkali-metal inductively coupled plasma (alkali-ICP) plays an important role in both atomic magnetometers and atomic clocks, producing these devices’ atomic signals through optical pumping. Unfortunately, though the alkali-ICP’s optical pumping efficiency grows exponentially with temperature, at relatively high temperatures (∼140 °C) the discharge transitions from “ring mode” to “red mode,” which is a spectral change in the plasma’s output that corresponds broadly to a transition from “good emission” for optical pumping to “poor emission.” Recently, evidence has accumulated pointing to radiation trapping as the mechanism driving the ring-mode to red-mode transition, suggesting that the phenomenon is primarily linked to the alkali vapor’s temperature. However, observations of the transition made in the 1960 s, demonstrating that the ICP temperature associated with the transition depended on rf-power, would appear to cast doubt on this mechanism. Here, we carefully investigate the influence of rf-power on the ring-mode to red-mode transition, finding that rf-power only affects the transition through discharge heating. Thus, the present work shows that the primary effect of rf-power on the ring-mode to red-mode transition can be understood in terms of the radiation trapping mechanism.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.80.Pi High-frequency and RF discharges
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Resonant planar antenna as an inductive plasma source

Ph. Guittienne, S. Lecoultre, P. Fayet, J. Larrieu, A. A. Howling, and Ch. Hollenstein

J. Appl. Phys. 111, 083305 (2012); http://dx.doi.org/10.1063/1.4705978 (6 pages)

Online Publication Date: 27 April 2012

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A resonant planar antenna as an inductive plasma source operating at 13.56 MHz inside a low pressure vacuum vessel is presented for potential plasma processing applications. Its principle consists in interconnecting elementary resonant meshes composed of inductive and capacitive elements. Due to its structure, the antenna shows a set of resonant modes associated with peaks of the real input impedance. Each of these modes is defined by its own current and voltage distribution oscillating at the frequency of the mode. A rectangular antenna of 0.55m×0.20m has been built, and first results obtained with argon plasmas are presented. Plasma generation is shown to be efficient as densities up to 4·1017m-3 at 2000 W have been measured by microwave interferometry at a distance of 4 cm from the source plane. It is also demonstrated that the plasma couples inductively with the resonating currents flowing in the antenna above a threshold power of about 60 W. A non-uniformity of less than ±5% is obtained at 1000 W at a few centimeters above the antenna over 75% of its surface.
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52.50.Dg Plasma sources
52.25.-b Plasma properties
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
84.40.Ba Antennas: theory, components and accessories

Space charge effects on externally injected current in planar diodes: Existence of multiple stationary states

A. Rokhlenko and J. L. Lebowitz

J. Appl. Phys. 111, 083306 (2012); http://dx.doi.org/10.1063/1.4706567 (7 pages) | Cited 1 time

Online Publication Date: 27 April 2012

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We study the effects of space charge on the properties of a system with a specified steady current. The problem is solved exactly for a planar one dimensional geometry, but we expect similar results for more realistic systems. We find that in many cases, the stationary current density cannot exceed some fixed value Jmax and in other cases be lower than a fixed Jmin depending on the method of injection. There are also intervals of intermediate current densities, which cannot exist in the stationary conditions. In general, there are values of J in some range where there are two different stationary regimes, which correspond to two different electric fields at the emitter surface. Connection with results obtained from numerical simulations and possible applications are also considered.
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85.45.Bz Vacuum microelectronic device characterization, design, and modeling
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Surface charging, discharging and chemical modification at a sliding contact

S. V. Singh, Y. Kusano, P. Morgen, and P. K. Michelsen

J. Appl. Phys. 111, 083501 (2012); http://dx.doi.org/10.1063/1.3698311 (8 pages)

Online Publication Date: 16 April 2012

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Electrostatic charging, discharging, and consequent surface modification induced by sliding dissimilar surfaces have been studied. The surface-charge related phenomena were monitored by using a home-built capacitive, non-contact electrical probe, and the surface chemistry was studied by X-ray photoelectron spectroscopy (XPS). The experiments were performed on the disk surface of a ball-on-rotating-disk apparatus; using a glass disk and a Teflon (polytetrafluoroethylene) ball arrangement, and a polyester disks and a diamondlike carbon (DLC) coated steel ball arrangement. The capacitive probe is designed to perform highly resolved measurements, which is sensitive to relative change in charge density on the probed surface. For glass and Teflon arrangement, electrical measurements show that the ball track acquires non-uniform charging. Here not only the increase in charge density, but interestingly, increase in number of highly charged regions on the ball track was resolved. Threefold increase in the number of such highly charged regions per cycle was detected immediately before the gas breakdown-like incidences compared to that of other charge/discharge incidences at a fixed disk rotation speed. We are also able to comment on the behavior and the charge decay time in the ambient air-like condition, once the sliding contact is discontinued. XPS analysis showed a marginal deoxidation effect on the polyester disks due to the charging and discharging of the surfaces. Moreover, these XPS results clearly indicate that the wear and friction (sliding without charging) on the surface can be discarded from inducing such a deoxidation effect.
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73.40.-c Electronic transport in interface structures
79.60.-i Photoemission and photoelectron spectra
81.40.Pq Friction, lubrication, and wear
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
62.20.Qp Friction, tribology, and hardness

Photoionization absorption and zero-field spin splitting of acceptor-bound magnetic polaron in p-type Hg1-xMnxTe single crystals

Liangqing Zhu, Jun Shao, Tie Lin, Xiang Lü, Junyu Zhu, Xiaodong Tang, and Junhao Chu

J. Appl. Phys. 111, 083502 (2012); http://dx.doi.org/10.1063/1.3702845 (8 pages)

Online Publication Date: 16 April 2012

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Temperature-dependent magnetic (2–300 K), DC Hall (10–300 K), and infrared transmission (11.5–300 K) measurements are performed on a series of p-type Hg1-xMnxTe (0.12 ≤ x ≤ 0.26) single crystals in the spin-glass regime. Photoionization absorption (PIA) of acceptor-bound magnetic polarons (acceptor-BMPs) is observed to evolve with temperature, which is better accounted for by the classical oscillator model than by the quantum defect method. At low temperatures, p-type Hg1−xMnxTe manifests distinct phenomena of paramagnetic enhancement, negative magnetoresistance, and decrease of the effective binding energy and blueshift of the PIA of the acceptor-BMPs with nearly the same degree as temperature declines. A spin-splitting model is proposed, which can well reproduce the experimentally observed zero-field spin splitting of the acceptor-BMP level at low temperatures and the increase of the spin splitting as temperature drops. The results suggest that the acceptor-BMPs in Hg1−xMnxTe may have potential applications in light-driven polaronic memories, tunable far-infrared lasers, and detectors.
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71.38.-k Polarons and electron-phonon interactions
75.50.Pp Magnetic semiconductors
78.30.Hv Other nonmetallic inorganics
72.20.My Galvanomagnetic and other magnetotransport effects
75.20.Ck Nonmetals
73.43.Qt Magnetoresistance

Delayed mechanical failure of the under-bump interconnects by bump shearing

Han Li, Thomas M. Shaw, Xiao-Hu Liu, and Griselda Bonilla

J. Appl. Phys. 111, 083503 (2012); http://dx.doi.org/10.1063/1.3702875 (5 pages)

Online Publication Date: 16 April 2012

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Packaging-induced stresses can cause mechanical failures of various forms in the Cu/low-k interconnects. Here we report a time-dependent failure mode of the interconnects underneath the copper pillar bump. Delayed catastrophic fracture is observed in the interconnect dielectrics when a sustained shear load is applied on the bump using a single bump shear setup. The time to failure is found to be highly sensitive to the load level and temperature, but not to the environmental humidity. However, moisture diffusion through intentionally broken moisture seal can accelerate the failure process. Quantitative analysis suggests the delayed failure can be well captured over a wide range of testing conditions by a model based on subcritical crack growth in the interconnect dielectrics.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mt Cracks
62.20.mm Fracture
66.30.-h Diffusion in solids

Transformation and clustering of defects induced by electron irradiation in barium hollandite ceramics for radioactive cesium storage: Electron paramagnetic resonance study

V. Aubin-Chevaldonnet, D. Gourier, D. Caurant, and J.-M. Costantini

J. Appl. Phys. 111, 083504 (2012); http://dx.doi.org/10.1063/1.3702892 (14 pages)

Online Publication Date: 16 April 2012

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Barium hollandite-type ceramics have been envisaged for the immobilization of radioactive cesium. To evaluate their stability under irradiation, a hollandite ceramic of composition Ba1.16Al2.32Ti5.68O16 was irradiated with electrons at a temperature close to room temperature to simulate the effect of β- and γ-decays of cesium. Ti3+ and O2- paramagnetic defects induced by electron irradiation [V. Aubin-Chevaldonnet et al., J. Phys.: Condens. Matter 18, 4007 (2006)] were detected by electron paramagnetic resonance. As the temperature in the bulk of the hollandite waste form could reach 300 °C at the beginning of the storage, the thermal stability of these paramagnetic defects was also studied. Isothermal annealing treatments at 300 °C and isochronal annealing treatments between 50 °C and 800 °C show that the irradiation induced Ti3+ (E1 and E2 centers) and O2− (H centers) do not recombine. Instead, they partially transform during annealing, respectively, into titanyl TiO+ centers (E3 centers) at the grain surface and into paramagnetic clusters of O2− of less than 10 nm size (G2 centers), trapped in the bulk of the grains. These oxygen-rich aggregates could prefigure the formation of molecular oxygen observed in electron irradiated glasses.
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76.30.Lh Other ions and impurities
61.72.-y Defects and impurities in crystals; microstructure
81.40.Gh Other heat and thermomechanical treatments
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism

First-principles study of shear behavior of Al, TiN, and coherent Al/TiN interfaces

S. K. Yadav, R. Ramprasad, A. Misra, and X.-Y. Liu

J. Appl. Phys. 111, 083505 (2012); http://dx.doi.org/10.1063/1.3703663 (5 pages) | Cited 1 time

Online Publication Date: 16 April 2012

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In this ab initio work, density functional theory was used to calculate the ideal shear strengths of pure Al, pure TiN, the Al/TiN interfacial region, and Al/TiN multilayers. The ideal shear strength of the Al/TiN interface was found to vary from very low (on the order of the ideal shear strength of Al) to very high (on the order of the ideal shear strength of TiN), depending on whether the TiN at the interface was Ti- or N-terminated, respectively. The results suggest that the shear properties of Al/TiN depend strongly on the chemistry of the interface, Al:N versus Al:Ti terminations. Nevertheless, for the Al/TiN multilayers, the ideal shear strength was limited by shear in the Al layer away from the interface, even when the individual layer thickness is less than a nanometer.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.35.Gy Mechanical properties; surface strains
FREE

Surface elasticity effect on the size-dependent elastic property of nanowires

Haiyan Yao (姚海燕), Guohong Yun (云国宏), Narsu Bai (白那日苏), and Jiangang Li (李建刚)

J. Appl. Phys. 111, 083506 (2012); http://dx.doi.org/10.1063/1.3703671 (6 pages) | Cited 1 time

Online Publication Date: 16 April 2012

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A modified core-shell (MC-S) model is proposed to investigate the effect of surface elasticity on the elastic properties of nanowires under bending and tension loading modes. The continuous exponential function based on bulk elasticity is applied to the surface region of nanowires to better describe the elasticity in the surface layer. Two parameters related to the surface, namely, the inhomogeneous degree constant math, and the transition region of this inhomogeneous state rs (i.e., surface layer thickness), are introduced for examining the size effects of the elastic modulus of the overall nanowires. A strong size dependence of elasticity is revealed under both bending and tension loads. Furthermore, the theoretical solution for an effective Young’s modulus with relevant experiments, as well as the results of a molecular statistical thermodynamics (MST) method for zinc oxide (ZnO) nanowires, and a molecular dynamics (MD) simulation for silicon (Si) nanowires, are compared. It is shown that the theoretical curves not only agree well with the experimental data, but also fit the computational results (MST or MD) approximately below 20 nm. As a result, our model can predict the behavior of surface elasticity, with respect to the lateral size of nanostructures at a relatively small scale, no matter how stiff or soft the surface of the nanomaterials.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.20.de Elastic moduli
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
05.20.-y Classical statistical mechanics

Ab initio study of vacancy and self-interstitial properties near single crystal silicon surfaces

Eiji Kamiyama, Koji Sueoka, and Jan Vanhellemont

J. Appl. Phys. 111, 083507 (2012); http://dx.doi.org/10.1063/1.4703911 (9 pages) | Cited 4 times

Online Publication Date: 16 April 2012

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The microscopic model of the Si(001) crystal surface was investigated by first principles calculations to clarify the behavior of intrinsic point defects during crystal growth and thermal annealing. A c(4 × 2) structure model was used to describe the crystal surface in contact with vacuum. The calculations show that a vacancy in the first or second atomic layer has about a 2.0 eV lower formation energy than deeper inside the bulk and that there is a diffusion barrier to penetrate into the deeper crystal region. Furthermore, a vacancy in the first or second atomic layer is stabilized by the fact that Si atoms with dangling bonds attract each other due to ionic and/or covalent bonding. There is, however, no barrier for the diffusion of a vacancy from the first layer to the second one. The tetrahedral (T)-site and dumbbell (DB)-site, in which a Si atom is captured from the surface and forms a self-interstitial, are found as stable sites near the third atomic layer. The T-site has a barrier of 0.48 eV, whereas the DB-site has no barrier for the interstitial to penetrate into the crystal from the vacuum. Self-interstitials in both the T- and DB-sites in the third atomic layer have a 1.7 to 2.8 eV lower formation energy than deeper in the bulk and there is a diffusion barrier to penetrate into the deeper crystal region; 32 sites were found as stable sub-surface vacancy positions, whereas only 8 sites were found as stable self-interstitial positions. Using these results, a mechanism for the elimination of crystal-originated pits by thermal annealing is proposed. It is shown that the microscopic model is consistent with and allows to fine-tune existing macroscopic models that are used to calculate the intrinsic point defects behavior during crystal growth from a melt.
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61.72.jj Interstitials
81.10.Fq Growth from melts; zone melting and refining
81.05.Cy Elemental semiconductors
71.55.Cn Elemental semiconductors
61.72.jd Vacancies
61.72.Cc Kinetics of defect formation and annealing

First-principles study of temperature-dependent optical properties of semiconductors from ultraviolet to infrared regions

J. Liu and L. H. Liu

J. Appl. Phys. 111, 083508 (2012); http://dx.doi.org/10.1063/1.4703922 (6 pages)

Online Publication Date: 16 April 2012

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We present a first-principles approach to take into account lattice vibration in calculating the ultraviolet-to-infrared optical response of semiconductors, without using any empirical parameters. Electron−phonon interactions are shown to be the main contributions to thermal corrections in the electronic band structure, whereas phonon−phonon interactions affect the infrared absorption spectra of polar semiconductors. Ranging from room temperature on up, the temperature-dependent dielectric functions of silicon for the ultraviolet-visible regions are calculated through combining the Allen-Heine-Cardona method with the Bethe-Salpeter equation. Temperature effects of the infrared optical spectra of gallium arsenide are also discussed; we use first-principles method to take into account anharmonic contributions. By introducing electron−phonon and phonon−phonon interactions, the calculated optical spectra show clear temperature dependence that is in good agreement with experimental data. Thermal expansion contributions are verified to be negligible compared to contribution from lattice vibration.
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78.20.N- Thermo-optic effects
71.15.-m Methods of electronic structure calculations
78.40.Fy Semiconductors
71.20.Nr Semiconductor compounds
78.30.Am Elemental semiconductors and insulators
78.30.Fs III-V and II-VI semiconductors

Complete parameterization of the dielectric function of microcrystalline silicon fabricated by plasma-enhanced chemical vapor deposition

Tetsuya Yuguchi, Yosuke Kanie, Nobuyuki Matsuki, and Hiroyuki Fujiwara

J. Appl. Phys. 111, 083509 (2012); http://dx.doi.org/10.1063/1.4704158 (8 pages) | Cited 1 time

Online Publication Date: 16 April 2012

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The dielectric functions of microcrystalline silicon (μc-Si:H) layers deposited by plasma-enhanced chemical vapor deposition have been determined by applying real-time spectroscopic ellipsometry (SE) in an attempt to construct an optical database for μc-Si:H. The μc-Si:H dielectric functions have been parameterized completely by a dielectric function model that employs two Tauc-Lorentz peaks combined with one Harmonic oscillator peak. This parameterization scheme has been applied successfully to describe the structural variation from hydrogenated amorphous silicon (a-Si:H) to highly crystallized μc-Si:H. Moreover, to express the microstructure of μc-Si:H, the μc-Si:H structural factor κ has been defined based on the amplitude of the E2 optical transition with a critical point energy of 4.3 eV. From the value of κ, a variety of Si microstructures, including complete a-Si:H phase (κ = 0), μc-Si:H with a-Si:H-rich grain boundaries (κ ∼ 0.5), and μc-Si:H with void-rich grain boundaries (κ = 1), can be distinguished. The μc-Si:H structures estimated from the above SE analyses show excellent correlation with those deduced from the Raman spectroscopy. From the SE analysis procedure developed in this study, the layer thickness as well as the microstructure of μc-Si:H can be characterized rather easily.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.05.Cy Elemental semiconductors
61.72.Mm Grain and twin boundaries
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Thermal boundary resistance for gold and CoFe alloy on silicon nitride films

Taehee Jeong, Jian-Gang Zhu, Suk Chung, and Matthew R. Gibbons

J. Appl. Phys. 111, 083510 (2012); http://dx.doi.org/10.1063/1.3703571 (7 pages) | Cited 1 time

Online Publication Date: 17 April 2012

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Advances in microelectronics technology strongly depend on the thermal optimization of metal/dielectric interfaces, which requires precise modeling and thermal characterization of metal/dielectric structures. This work experimentally investigated the influence of metallic layers on the thermal boundary resistance of silicon nitride dielectric material. The results reveal that the thermal boundary resistance of silicon nitride thin films depends on the metallic layers. The thermal boundary resistance at the interface between Au and SiNx is larger than that between Co0.9Fe0.1 and SiNx. The reasons to cause this difference are discussed with phonon transmission probability and the ratio of the Debye temperature between metals and dielectrics.
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68.35.Ct Interface structure and roughness
44.20.+b Boundary layer heat flow
77.55.-g Dielectric thin films
02.50.-r Probability theory, stochastic processes, and statistics
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