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1 Aug 2010

Volume 108, Issue 3, Articles (03xxxx)

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back to top Lasers, Optics, and Optoelectronics

Axial polarizers based on dichroic liquid crystals

Sarik Nersisyan, Nelson Tabiryan, Diane M. Steeves, and Brian R. Kimball

J. Appl. Phys. 108, 033101 (2010); http://dx.doi.org/10.1063/1.3460810 (5 pages) | Cited 2 times

Online Publication Date: 4 August 2010

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Polarizers capable of producing linearly polarized beams with axial (radial and azimuthal) symmetry have been fabricated with the aid of a dichroic liquid crystal. Photoalignment was achieved using a printing technique to reduce the UV exposure time required for production of axially aligning substrates from 1 h, typical for direct writing techniques, to 10 min. The polarizing features of axial polarizers and their pairs are characterized and their differences outlined. We demonstrate that the transmission switching contrast of an axial polarizer/analyzer pair, comprised of an electrically controlled liquid crystal cell, is comparable to conventional systems with linear polarizers. The opportunities for using axial polarizers for polarization imaging, sensor protection, and nonlinear optics are discussed. Particularly, we show that the technology could reduce the fluence of a laser beam on an optical sensor without affecting imaging.
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42.79.Ci Filters, zone plates, and polarizers
78.20.Fm Birefringence
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Side-polished fiber Bragg grating refractive index sensor with TbFeCo magnetoptic thin film

Minghong Yang, Jixiang Dai, Xiaobin Li, and Junjie Wang

J. Appl. Phys. 108, 033102 (2010); http://dx.doi.org/10.1063/1.3466981 (4 pages) | Cited 1 time

Online Publication Date: 4 August 2010

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Fiber Bragg grating (FBG) is side-polished to enable interaction with sensitive materials around FBG fiber core. Using TbFeCo magneto-optic thin film deposited onto FBG fiber core as transducer, a FBG refractive index senor for magnetic field/current characterization is first proposed and demonstrated in this paper. Magnetic field sensing experiments show 19 pm of wavelength shift at a magnetic field intensity of 50 mT, the average linearity of magnetic field response is 0.9877.
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42.81.Pa Sensors, gyros
42.79.Dj Gratings

Laser-induced damage threshold of silicon in millisecond, nanosecond, and picosecond regimes

X. Wang (王茜), Z. H. Shen (沈中华), J. Lu (陆廴), and X. W. Ni (倪晓武)

J. Appl. Phys. 108, 033103 (2010); http://dx.doi.org/10.1063/1.3466996 (7 pages) | Cited 7 times

Online Publication Date: 4 August 2010

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Millisecond, nanosecond, and picosecond laser pulse induced damage thresholds on single-crystal are investigated in this study. The thresholds of laser-induced damage on silicon are calculated theoretically for three pulse widths based on the thermal damage model. An axisymmetric mathematical model is established for the transient temperature field of the silicon. Experiments are performed to test the damage thresholds of silicon at various pulse widths. The results indicate that the damage thresholds obviously increase with the increasing of laser pulse width. Additionally, the experimental results agree well with theoretical calculations and numerical simulation results.
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81.05.Cy Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Eb Laser ablation

External efficiency and carrier loss mechanisms in InAs/GaInNAs quantum dot light-emitting diodes

M. Montes, A. Hierro, J. M. Ulloa, A. Guzmán, M. Al Khalfioui, M. Hugues, B. Damilano, and J. Massies

J. Appl. Phys. 108, 033104 (2010); http://dx.doi.org/10.1063/1.3467004 (8 pages)

Online Publication Date: 4 August 2010

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The electroluminescence (EL) characteristics of a set of InAs/GaInNAs quantum dot (QD) light-emitting diodes with varying In and N contents are analyzed. Room-temperature EL around 1.5 μm is obtained with 15% In and 2% N in the QD capping layer. It is shown that the addition of N results in a degradation of the external efficiency, ηext, probably due to an increase in the nonradiative recombination in the QD heterostructure and an increase in the carrier escape from the QD to the capping layer, which yield a degradation of the current injection efficiency into the QD. Nevertheless, ηext can be partially recovered if a postgrowth rapid thermal annealing is performed, although this also results in a blueshift in the EL peak wavelength. The different contributions to the EL spectra are also analyzed and identified by looking at their dependence on injected current and temperature. It is found that N-containing devices show two radiative transitions. The lowest energy transition has been ascribed to the QD ground state recombination, whereas the higher energy transition has been attributed to recombination of carriers confined in the capping layer. Moreover, the carrier loss mechanisms responsible for the quenching of the EL in the dilute nitride-based devices are studied. It is found that the EL thermal quenching has an activation energy which can be ascribed to carrier escape from the QD to the capping layer.
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85.60.Jb Light-emitting devices

Theoretical modeling of refractive index in ion implanted LiNbO3 waveguides

Jiao-Jian Yin, Fei Lu, Xian-Bing Ming, Yu-Jie Ma, and Meng-bing Huang

J. Appl. Phys. 108, 033105 (2010); http://dx.doi.org/10.1063/1.3467529 (5 pages) | Cited 1 time

Online Publication Date: 4 August 2010

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A theoretical model is developed to evaluate the roles of various mechanisms, including the molar polarization and molar volume, the spontaneous polarization and the photoelastic effect, for the modifications of refractive indices in ion-implanted LiNbO3 waveguides. Based on the model, numerical calculations of refractive indices as a function of the lattice damage level in LiNbO3 crystals of different crystalline orientations (X, Y, and Z), are performed, with results in a good agreement with experimental data. The analysis indicates that the spontaneous polarization, the molar polarization, and molar volume play important roles in determining the index profiles in ion implanted LiNbO3. In addition, the contribution of the strain-induced photoelastic effect has been identified for different damage levels.
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42.79.Gn Optical waveguides and couplers
42.70.-a Optical materials
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.up Other materials
81.40.Tv Optical and dielectric properties related to treatment conditions

Energy transfer between Eu–Mn and photoluminescence properties of Ba0.75Al11O17.25–BaMgAl10O17:Eu2+,Mn2+ solid solution

Jun Zhou, Yuhua Wang, Bitao Liu, and Feng Li

J. Appl. Phys. 108, 033106 (2010); http://dx.doi.org/10.1063/1.3460280 (6 pages) | Cited 5 times

Online Publication Date: 5 August 2010

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In order to evaluate the energy transfer between Eu–Mn in Ba0.75Al11O17.25–BaMgAl10O17 solid solution, Ba0.75Al11O17.25–BaMgAl10O17:Eu2+,Mn2+ phosphors were prepared by flux method. The crystal structure and the morphology of the solid solution were demonstrated by x-ray dirrfactometer and scanning electron microscopy. The photoluminescence mechanisms were explained by the energy transfer of Eu2+ to Mn2+ and the Dexter theory. A redshift of green emission peak and a decrease in decay time with the increase in Mn2+ concentration were observed. These phenomena are attributed to the formation of Mn2+ paired centers after analysis by a method of Pade approximations.
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78.55.Hx Other solid inorganic materials
61.50.-f Structure of bulk crystals

Design of an electrically pumped SiGeSn/GeSn/SiGeSn double-heterostructure midinfrared laser

G. Sun, R. A. Soref, and H. H. Cheng

J. Appl. Phys. 108, 033107 (2010); http://dx.doi.org/10.1063/1.3467766 (6 pages) | Cited 10 times

Online Publication Date: 5 August 2010

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This paper presents the conception, modeling, and simulation of a silicon-based group-IV semiconductor injection laser diode in which the GeSn-alloy active region has a direct band gap wavelength in the 1.8 to 3.0 μm midwave infrared for 6%–12% α-Sn. The strain-free monolithic P-type semiconductor/Intrinsic semiconductor/N-type semiconductor (PIN) bulk heterostructure, grown lattice matched upon a relaxed GeSn-buffer on silicon-on-insulator, is believed to be manufacturable in a complementary metal-oxide semiconductor fab. Detailed modeling is given for the type-I band offsets, carrier lifetimes, infrared gain profile and laser threshold current density Jth in a Fabry–Perot cavity having 20–100 cm−1 loss. The laser’s temperature of operation is determined by a combination of the radiative lifetime and the nonradiative lifetime due to unwanted Auger electron-hole recombination. If we keep Jth below 10 kA/cm2, then we find that this laser requires cooling in the 100–200 K range, whereas Jth at 300 K appears to be too high for a practical device. However, the GeSn quantum-well laser diode does offer a pathway to room-temperature operation.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Highly doped layers as efficient electron–hole recombination contacts for tandem organic solar cells

Ronny Timmreck, Selina Olthof, Karl Leo, and Moritz K. Riede

J. Appl. Phys. 108, 033108 (2010); http://dx.doi.org/10.1063/1.3467786 (6 pages) | Cited 18 times

Online Publication Date: 5 August 2010

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A key feature of stacked organic solar cells is an efficient recombination contact at the interface between the solar cells in the stack. Here, an electron current has to be converted into a hole current without loss of energy. Furthermore, the recombination contact has to be highly transparent. We present a new approach for small molecule organic solar cells using highly doped organic layers. Our approach adapts the use of tunnel diodes known from inorganic tandem solar cells. We compare a metal cluster based recombination contact reported in literature to the new approach using different organic tandem solar cell structures. For this purpose, current-voltage characteristics of adequate solar cells are measured. The experiments show that highly doped layers as recombination contacts in tandem organic solar cells are superior to the metal cluster based approach. The proposed concept allows an addition of the open circuit voltages of the subcells of a tandem solar cell, without absorption or reflection at the recombination contact. The results further show that our concept does not depend on the specific choice of materials as it is seen for metal cluster based recombination contacts. It therefore represents a general approach which is compatible to mass manufacturing.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
68.65.Ac Multilayers
85.40.Ry Impurity doping, diffusion and ion implantation technology
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
88.40.jr Organic photovoltaics
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Thickness evaluation of InGaAs/InAlAs quantum wells

N. Kotera, K. Tanaka, H. Nakamura, and M. Washima

J. Appl. Phys. 108, 033109 (2010); http://dx.doi.org/10.1063/1.3457787 (12 pages)

Online Publication Date: 6 August 2010

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This work proposes a new optoelectronic measurement of quantum well (QW) thickness and applies it to doped and undoped In0.53Ga0.47As/In0.52Al0.48As multiple-QW structures. Near-infrared spectroscopic identification of the interband optical transition at 100–300 K gave the eigenenergies of the conduction band in the QW. Evaluation of the QW thickness involved analysis of the effective mass at the corresponding eigenenergy. QW thicknesses in the range of 5.45–20.8 nm were determined in six different wafers. These thicknesses agreed well with the QW thicknesses estimated by double-crystal x-ray diffraction within almost two monolayers. This measurement was used to determine the distance of potential boundaries confining the electron wave functions.
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78.67.De Quantum wells
81.07.St Quantum wells
71.20.Nr Semiconductor compounds
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
78.30.Fs III-V and II-VI semiconductors

Mechanism of femtosecond-laser induced refractive index change in phosphate glass under a low repetition-rate regime

Douglas J. Little, Martin Ams, Peter Dekker, Graham D. Marshall, and Michael J. Withford

J. Appl. Phys. 108, 033110 (2010); http://dx.doi.org/10.1063/1.3468490 (5 pages) | Cited 6 times

Online Publication Date: 9 August 2010

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Raman microscopy and refractive near-field profilometry were used to analyze waveguides written in Yb-doped Kigre QX glass under the low repetition-rate (noncumulative-heating) regime. It was found that femtosecond-laser induced refractive index change was due to an increase in the proportion of Q1 P-tetrahedra and the associated increase in the polarizability of the glass. The role of color center formation and removal in this process is clearly defined, phosphorous–oxygen hole centers (POHCs) and PO3− ions form as a result of P–O bonds being broken during the modification process, and the subsequent removal of POHCs give rise to the increased proportion of Q1 P-tetrahedra. This result, when compared to other studies undertaken in the cumulative-heating regime, show conclusively that the mechanism of refractive index change in a particular type of glass can be very different, depending on the irradiation conditions.
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42.70.Ce Glasses, quartz
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Gn Optical waveguides and couplers

Microfabrication of polystyrene microbead arrays by laser induced forward transfer

Alexandra Palla-Papavlu, Valentina Dinca, Iurie Paraico, Antoniu Moldovan, James Shaw-Stewart, Christof W. Schneider, Eugenia Kovacs, Thomas Lippert, and Maria Dinescu

J. Appl. Phys. 108, 033111 (2010); http://dx.doi.org/10.1063/1.3466746 (6 pages) | Cited 8 times

Online Publication Date: 10 August 2010

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In this study we describe a simple method to fabricate microarrays of polystyrene microbeads (PS-μbeads) on Thermanox coverslip surfaces using laser induced forward transfer (LIFT). A triazene polymer layer which acts as a dynamic release layer and propels the closely packed microspheres on the receiving substrate was used for this approach. The deposited features were characterized by optical microscopy, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. Ultrasonication was used to test the adherence of the transferred beads. In addition, the laser ejection of the PS-μbead pixels was investigated by time resolved shadowgraphy. It was found that stable PS-μbeads micropatterns without any specific immobilization process could be realized by LIFT. These results highlight the increasing role of LIFT in the development of biomaterials, drug delivery, and tissue engineering.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.16.Mk Laser-assisted deposition
42.62.-b Laser applications

Hot electron effects on efficiency degradation in InGaN light emitting diodes and designs to mitigate them

X. Ni, X. Li, J. Lee, S. Liu, V. Avrutin, Ü. Özgür, H. Morkoç, and A. Matulionis

J. Appl. Phys. 108, 033112 (2010); http://dx.doi.org/10.1063/1.3460271 (13 pages) | Cited 8 times

Online Publication Date: 10 August 2010

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Hot electrons and the associated ballistic and quasiballistic transport, heretofore neglected endemically, across the active regions of InGaN light emitting diodes (LEDs) have been incorporated into a first order simple model which explains the experimental observations of electron spillover and the efficiency degradation at high injection levels. The model is in good agreement with experiments wherein an adjustable barrier hot electron stopper, commonly called the electron blocking layer (EBL), is incorporated. The model is also in agreement with experiments wherein the electrons are cooled, eliminating hot electrons, inside a staircase electron injector (SEI) prior to their injection into the active region. Thermionic emission from the active region, even if one uses an uncharacteristically high junction temperature of 1000 K, fails to account for the carrier spillover and the experimental observations in our laboratory in samples with varying EBL barrier heights. The model has been successfully applied to both m-plane (lacking polarization induced electric field) and c-plane (with polarization induced field) InGaN double heterostructure (DH) LEDs with a 6 nm active region featuring a variable barrier hot electron stopper, and a SEI, and the various combinations thereof. The choice of DH LEDs stems from our desire to keep the sample structure simple as well as the model calculations. In this paper, the theoretical and experimental data along with their comparison followed by an insightful discussion are given. The model and the approaches to eliminate carrier spillover proposed here for InGaN LEDs are also applicable to GaN-based laser diodes.
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72.20.Ht High-field and nonlinear effects
72.30.+q High-frequency effects; plasma effects
79.40.+z Thermionic emission
85.60.Jb Light-emitting devices

Long-lived laser-induced microwave plasma guides in the atmosphere: Self-consistent plasma-dynamic analysis and numerical simulations

M. N. Shneider, A. M. Zheltikov, and R. B. Miles

J. Appl. Phys. 108, 033113 (2010); http://dx.doi.org/10.1063/1.3457150 (8 pages) | Cited 11 times

Online Publication Date: 11 August 2010

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A detailed model of plasma dynamics, which self-consistently integrates plasma-kinetic, Navier–Stokes, electron heat conduction, and electron-vibration energy transfer equations, is used to quantify the limitations on the lifetime of microwave plasma waveguides induced in the atmosphere through filamentation with high-intensity ultrashort laser pulses further sustained by long laser pulses. We demonstrate that a near-infrared or midinfrared laser pulse can tailor plasma decay in the wake of a filament, efficiently suppressing, through electron temperature increase, the attachment of electrons to neutral species and dissociative recombination, thus substantially increasing the plasma-guide lifetime and facilitating long-distance transmission of microwaves.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
47.10.ad Navier-Stokes equations

The effects of nanopillar surface texturing on the photoluminescence of polymer films

Taehyung Kim, Dharmalingam Kurunthu, Jonathan J. Burdett, and Christopher J. Bardeen

J. Appl. Phys. 108, 033114 (2010); http://dx.doi.org/10.1063/1.3457147 (6 pages) | Cited 2 times

Online Publication Date: 13 August 2010

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We report on the enhancement of photoluminescence (PL) from polymer thin films by nanotexturing their surfaces using nanoporous anodic alumina oxide templates. Chromophore-embedded polystyrene films with nanostructured surfaces are prepared by imprinting 200 nm diameter nanopillars with various heights, and their PL output and angular emission are observed. The PL output increases and the angular distributions broaden as the height of the nanopillars increases. For 5 μm tall nanopillars, the PL output is enhanced by a factor of 2.5 relative to the smooth surface. An effective refractive index model provides a qualitative description of the angular emission and PL output of nanotextured surface but underestimates the degree of PL enhancement. Comparison of the nanopillared films with surfaces randomly roughened using sandpaper shows that the details of the texturing have a significant impact on the PL output characteristics. These results show that imprinted nanopillars provide a simple and controlled way to increase the PL output of luminescent polymer films.
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68.55.am Polymers and organics
78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds
68.55.jm Texture
68.35.bm Polymers, organics
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
back to top Plasmas and Electrical Discharges

Electrical and kinetic model of an atmospheric rf device for plasma aerodynamics applications

Mario J. Pinheiro and Alexandre A. Martins

J. Appl. Phys. 108, 033301 (2010); http://dx.doi.org/10.1063/1.3383056 (9 pages) | Cited 5 times

Online Publication Date: 4 August 2010

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The asymmetrically mounted flat plasma actuator is investigated using a self-consistent two-dimensional fluid model at atmospheric pressure. The computational model assumes the drift-diffusion approximation and uses a simple plasma kinetic model. It investigated the electrical and kinetic properties of the plasma, calculated the charged species concentrations, surface charge density, electrohydrodynamic forces, and gas speed. The present computational model contributes to understand the main physical mechanisms, and suggests ways to improve its performance.
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52.25.-b Plasma properties
47.85.L- Flow control
52.25.Fi Transport properties
47.65.-d Magnetohydrodynamics and electrohydrodynamics
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.80.Pi High-frequency and RF discharges
07.05.Tp Computer modeling and simulation

Atmospheric pressure plasma jets beyond ground electrode as charge overflow in a dielectric barrier discharge setup

Nan Jiang, Ailing Ji, and Zexian Cao

J. Appl. Phys. 108, 033302 (2010); http://dx.doi.org/10.1063/1.3466993 (5 pages) | Cited 4 times

Online Publication Date: 4 August 2010

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With a proper combination of applied voltage and the width of ground electrode, atmospheric pressure plasma jets extending beyond the ground electrode, whether it sits on the downstream or the upstream side, can be equally obtained with a dielectric barrier discharge setup, which can be ascribed to the overflow of deposited charges [ J. Appl. Phys. 106, 013308 (2009) ]. Here, we show that, by using narrower ground electrodes, such an overflow jet can be successfully launched at a much reduced voltage (down to below 10 kV). Moreover, by using transparent and triadic ground electrodes, development of charge overflow beneath the ground electrode was temporally and spatially resolved. Temporal evolution of discharge currents measured on the severed ground electrode helps establish the propagation dynamics of discharges along the dielectric surface beneath ground electrode, and also reinforces the conception that the streamer’s head is in connection to the active electrode via a conducting channel. A small propagation velocity of 3.3×103 m/s was measured for the “overflow” jet inside the dielectric tube. The availability of such overflow jets is enormously advantageous concerning their application to living bodies, to which the high voltage at active electrode is lethally dangerous.
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52.75.-d Plasma devices
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.-s Electric discharges
52.25.Fi Transport properties

Investigation of the roles of gas-phase CF2 molecules and F atoms during fluorocarbon plasma processing of Si and ZrO2 substrates

Michael F. Cuddy and Ellen R. Fisher

J. Appl. Phys. 108, 033303 (2010); http://dx.doi.org/10.1063/1.3467776 (9 pages) | Cited 3 times

Online Publication Date: 5 August 2010

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The molecular-level chemistry involved in the processing of silicon and zirconia substrates by inductively coupled fluorocarbon (FC) plasmas produced from CF4 and C2F6 precursors has been explored. The roles of gas-phase excited, neutral, and ionic species, especially CF2 and F, were examined as they contribute to FC film formation and substrate etching. The surface reactivity of CF2 radicals in C2F6 plasmas has a dependence on substrate material and plasma system, as measured by our imaging of radicals interacting with surfaces (IRIS) technique. Relative concentrations of excited state species are also dependent upon substrate type. Moreover, differences in the nature and concentrations of gas-phase species in CF4 and C2F6 plasmas contribute to markedly different surface compositions for FC films deposited on substrates as revealed from x-ray photoelectron spectroscopic analysis. These data have led to the development of a scheme that illustrates the mechanisms of film formation and destruction in these FC/substrate systems with respect to CF2 and F gas-phase species and also Si and ZrO2 substrates.
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52.77.-j Plasma applications
52.50.-b Plasma production and heating

Ion focusing in enhanced glow discharge plasma immersion ion implantation of hydrogen and nitrogen into silicon

Qiu Yuan Lu, Zhuo Wang, Liu He Li, Ricky K. Y. Fu, and Paul. K. Chu

J. Appl. Phys. 108, 033304 (2010); http://dx.doi.org/10.1063/1.3467967 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2010

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Ion focusing in enhanced glow discharge plasma immersion ion implantation (EGD-PIII) of hydrogen into silicon affects the lateral ion fluence uniformity. The phenomenon and its effects are investigated experimentally and theoretically under different conditions and compared to those in nitrogen EGD-PIII. Consistent results are obtained from experiments and numerical simulation disclosing that the lower the plasma density, the more severe is the ion focusing effect. The influence of the negative high voltage on the ion focusing effect is small compared to that of the plasma density.
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52.77.Dq Plasma-based ion implantation and deposition
52.80.Hc Glow; corona
52.25.-b Plasma properties
81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
52.65.Rr Particle-in-cell method

Experiments and global model of inductively coupled rf Ar/N2 discharges

Takashi Kimura and Hiroki Kasugai

J. Appl. Phys. 108, 033305 (2010); http://dx.doi.org/10.1063/1.3468603 (9 pages) | Cited 12 times

Online Publication Date: 9 August 2010

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Experiments with a Langmuir probe and optical emission spectroscopy are carried out in inductively coupled rf (13.56 MHz) Ar/N2 discharges at three total pressures of 30, 60, and 110 mTorr, varying the Ar fractions from 50% to 95%. The electron energy probability functions (EEPFs) measured at all Ar fractions can be approximated using different exponentials in the bulk and high-energy regions, resulting in two temperature approximation of the measured EEPFs. The electron density slightly increases with increasing the Ar fraction at the Ar fractions below 70%, beyond which it relatively abruptly increases. On the other hand, the electron temperatures gradually decrease with the increase in the Ar fraction. The vibrational temperature does not strongly depend on the Ar fraction, whereas the rotational temperature gradually increases with the increase in the Ar fraction. The density of nitrogen atoms remains constant at the Ar fractions below 80%, beyond which it monotonically decreases with increasing the Ar fraction. A global model for electropositive plasma is used in order to investigate the plasma chemistry in Ar/N2 discharges assuming the Maxwellian electron energy distribution. The model results are compared with the experimental results, obtaining reasonably good agreement.
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52.70.Ds Electric and magnetic measurements
52.25.-b Plasma properties
52.80.-s Electric discharges
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Atomic-scale boron redistribution during reactive diffusion in Ni–Si

O. Cojocaru-Mirédin, D. Mangelinck, and D. Blavette

J. Appl. Phys. 108, 033501 (2010); http://dx.doi.org/10.1063/1.3456005 (6 pages) | Cited 1 time

Online Publication Date: 3 August 2010

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The redistribution of boron during the formation of the Ni silicides was investigated using atom probe tomography and transmission electron microscopy. A 7 nm amorphous intermixed region was found after deposition of a 30 nm thick Ni film at room temperature. The formation of this Ni–Si layer was found to have almost no influence on the boron implantation profile. After heating at 290 °C for 1 h, three types of silicides (Ni2Si, NiSi, and NiSi2) were identified below a thin remaining film of Ni (8 nm). The unexpected presence of the silicon-rich NiSi2 phase at this temperature may be caused by the presence of a thin silicon oxide (SiO2) observed at the Ni/Ni2Si interface that may act as a diffusion barrier. The average boron profile in NiSi2 and NiSi silicides is similar to the profile in the silicon substrate before reaction. A segregation of boron at several interfaces was detected. Small boron clusters (1.5 at. %) were found in NiSi, NiSi2, and Si phases but not in Ni2Si. After a 1 min heat treatment at 450 °C, the NiSi phase is the only silicide present. Boron clusters with a platelet shape and a concentration of 3 to 5 at. % of boron were found in both NiSi and Si. The presence of boron in the Ni silicide and its precipitation in the form of tiny clusters is likely to affect the electrical properties of the contacts.
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68.35.Fx Diffusion; interface formation
81.40.Gh Other heat and thermomechanical treatments
81.30.Mh Solid-phase precipitation
61.72.sh Impurity distribution

Thermal stability of SrTiO3/SiO2/Si Interfaces at Intermediate Oxygen Pressures

G. J. Yong, Rajeswari M. Kolagani, S. Adhikari, W. Vanderlinde, Y. Liang, K. Muramatsu, and S. Friedrich

J. Appl. Phys. 108, 033502 (2010); http://dx.doi.org/10.1063/1.3460098 (8 pages) | Cited 3 times

Online Publication Date: 3 August 2010

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The thermal stability of epitaxial SrTiO3 thin films grown by molecular-beam epitaxy on Si (001) has been studied using x-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and thermodynamic calculations. Our studies focus on the stability of the SrTiO3/Si structures under the conditions typically employed in the pulse laser deposition (PLD) growth of complex metal oxide heteroepitaxy on Si. We observe additional Bragg peaks in thermally treated SrTiO3 buffered Si structures, corresponding to possibly TiSi2 and/or SrSiO3, reaction products which are consistent with the reaction schemes we propose. In addition, OM and SEM reveal microstructures that are not readily accounted for solely by the solid state reactions as put forth by previous workers but can be reasonably explained by our proposed reaction schemes. Using our observations and thermodynamic analysis, we argue that reactions involving the gaseous species SiO(g), the reactivity of which has not been previously considered in this system, are important. We attribute the onset of degradation of the SrTiO3 film at high temperatures, to the circular void forming reaction Si(s)+SiO2(s)→2SiO(g) at the interface and suggest that the reactions considered by previous workers involving all solid state reactants occurs only at the conclusion of degradation. Our results points to the need for keeping the PLD temperature as low as possible to minimize the production of reactive SiO(g) in avoiding the deleterious reactions.
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68.60.Dv Thermal stability; thermal effects
68.55.A- Nucleation and growth
77.84.Cg PZT ceramics and other titanates
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Molecular-beam epitaxy of AlInN: An effect of source flux and temperature on indium atom incorporation in alloys

Z. Y. Wang, B. M. Shi, Y. Cai, N. Wang, and M. H. Xie

J. Appl. Phys. 108, 033503 (2010); http://dx.doi.org/10.1063/1.3456009 (6 pages) | Cited 3 times

Online Publication Date: 3 August 2010

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Growth of AlInN alloys by molecular-beam epitaxy is studied by reflection high-energy electron diffraction, where in-plane lattice constant and specular beam intensity oscillations are recorded for information of lattice misfit and growth rate as a function of source flux and temperature. An unexpected dependence of alloy growth rate on indium flux is observed, which reflects the specific incorporation kinetics of indium in the alloy.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Polarization Raman spectroscopy of GaN nanorod bundles

T. Tite, C. J. Lee, and Y.-M. Chang

J. Appl. Phys. 108, 033504 (2010); http://dx.doi.org/10.1063/1.3460811 (6 pages) | Cited 1 time

Online Publication Date: 4 August 2010

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We performed polarization Raman spectroscopy on single wurtzite GaN nanorod bundles grown by plasma-assisted molecular beam epitaxy. The obtained Raman spectra were compared with those of GaN epilayer. The spectral difference between the GaN nanorod bundles and epilayer reveals the relaxation of Raman selection rules in these GaN nanorod bundles. The deviation of polarization-dependent Raman spectroscopy from the prediction of Raman selection rules is attributed to both the orientation of the crystal axis with respect to the polarization vectors of incident and scattered light and the structural defects in the merging boundary of GaN nanorods. The presence of high defect density induced by local strain at the merging boundary was further confirmed by transmission electron microscopy. The averaged defect interspacing was estimated to be around 3 nm based on the spatial correlation model.
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81.07.Bc Nanocrystalline materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.-j Plasma applications

Effect of pre-existing disorder on surface amorphization in GaN

A. Yu. Azarov, A. I. Titov, and S. O. Kucheyev

J. Appl. Phys. 108, 033505 (2010); http://dx.doi.org/10.1063/1.3462380 (5 pages) | Cited 2 times

Online Publication Date: 4 August 2010

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Single crystal GaN epilayers with pre-existing surface disordered layers are bombarded at room temperature with 40 and 100 keV P ions. Stable lattice defects are studied by Rutherford backscattering/channeling spectrometry. Results show that the rate of planar surface amorphization is independent of the concentration of pre-existing defects near the amorphous/crystalline (a/c) interface. In contrast, the formation of stable defects in the crystal bulk in the vicinity of an a/c interface is influenced by the presence of the interface. These experimental observations suggest that the a/c interface, as compared to stable bulk damage, is a more efficient sink for mobile point defects with respect to both processes of point defect recombination and trapping.
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81.65.-b Surface treatments
71.55.Eq III-V semiconductors
61.72.J- Point defects and defect clusters
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Remarkable enhancement in crystalline perfection, second harmonic generation efficiency, optical transparency, and laser damage threshold in potassium dihydrogen phosphate crystals by L-threonine doping

S. K. Kushwaha, Mohd. Shakir, K. K. Maurya, A. L. Shah, M. A. Wahab, and G. Bhagavannarayana

J. Appl. Phys. 108, 033506 (2010); http://dx.doi.org/10.1063/1.3456995 (7 pages) | Cited 6 times

Online Publication Date: 4 August 2010

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Effect of L-threonine (LT) doping on crystalline perfection, second harmonic generation (SHG) efficiency, optical transparency, and laser damage threshold (LDT) in potassium dihydrogen phosphate (KDP) crystals grown by slow evaporation solution technique (SEST) has been investigated. The influence of doping on growth rate and morphology of the grown crystals has also been studied. Powder x-ray diffraction data confirms the crystal structure of KDP and shows a systematic variation in intensity of diffraction peaks in correlation with morphology due to varying LT concentration. No extra phase formation was observed which is further confirmed by Fourier transform Raman (FT-Raman) studies. High-resolution x-ray diffraction curves indicate that crystalline perfection has been improved to a great extent at low concentrations with a maximum perfection at 1 mol % doping. At higher concentrations (5 to 10 mol %), it is slightly reduced due to excess incorporation of dopants at the interstitial sites of the crystalline matrix. LDT has been increased considerably with increase in doping concentration, whereas SHG efficiency was found to be maximum at 1 mol % in correlation with crystalline. The optical transparency for doped crystals has been increased as compared to that of pure KDP with a maximum value at 1 mol % doping.
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81.10.Dn Growth from solutions
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.66.Fn Inorganic compounds
61.72.up Other materials
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