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1 Sep 2005

Volume 98, Issue 5, Articles (05xxxx)

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Measurements of low-level prepulse on Nike KrF laser

Max Karasik, A. N. Mostovych, R. H. Lehmberg, Y. Chan, J. L. Weaver, and S. P. Obenschain

J. Appl. Phys. 98, 053101 (2005); http://dx.doi.org/10.1063/1.2032619 (8 pages) | Cited 1 time

Online Publication Date: 6 September 2005

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The krypton fluoride (KrF) laser is a leading candidate driver for inertial fusion energy. Some of the current fusion target designs call for targets with thin metallic coatings. These targets could be particularly susceptible to preheat by a low-level laser prepulse. Knowledge of the prepulse can be important in understanding and modeling the behavior of such targets. This paper presents measurements of low-level prepulse on target with the Nike KrF laser. Sources of prepulse are discussed and measurements are performed under several specific laser conditions in order to evaluate the relative contribution of these sources to the overall prepulse. Prepulse is found to be ∼ 2×10−7 from peak intensity for approximately 120 ns prior to the main laser pulse. Prepulse energy density on target is ∼ 2 J/cm2. The first laser amplifier in the time- and angle-multiplexed section of the laser is found to be the dominant source of prepulse.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
28.52.Av Theory, design, and computerized simulation

A study of transparent contact to vertical GaN-based light-emitting diodes

D. W. Kim, H. Y. Lee, G. Y. Yeom, and Y. J. Sung

J. Appl. Phys. 98, 053102 (2005); http://dx.doi.org/10.1063/1.2007850 (4 pages) | Cited 8 times

Online Publication Date: 7 September 2005

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In this study, transparent indium tin oxide (ITO) deposited by sputtering was applied to laser lift-off (LLO) GaN-based vertical light-emitting diodes (VLEDs) and the electrical and optical properties of ITO films were measured as a function of annealing conditions. The measured minimum resistivity of ITO film was about 3.78×10−4 Ω cm and the measured optical transmittance at 460 nm was 96.8% after the annealing process. In this condition, about 1×10−5 Ω cm2 of ITO contact resistance to LLO n-GaN could be obtained. By applying the transparent ITO layer to the LLO GaN-based VLEDs, a significant decrease of the forward operating voltage from 3.3 to 3.8 V at 20 mA could be obtained.
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85.60.Jb Light-emitting devices
78.66.Fd III-V semiconductors
73.40.Cg Contact resistance, contact potential
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Aluminum nitride emission from a laser-induced plasma in a dispersed aerosol

Nick Glumac

J. Appl. Phys. 98, 053301 (2005); http://dx.doi.org/10.1063/1.2034086 (6 pages) | Cited 1 time

Online Publication Date: 2 September 2005

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Emission from gas-phase AlN has been observed from a laser spark in a dilute suspension of AlN and Al nanoparticles in gaseous nitrogen. AlN emits most strongly in the 10–100-μs time period after laser excitation, and the emission is strong enough to be analyzed at moderately high dispersions. Under these high-temperature conditions, the population of high rotational levels results in there being a greater number of transitions than was observed by previous investigators, suggesting that the upper-state predissociation is fairly weak, and transitions over a much wider range of wavelengths are accessible for absorption-based diagnostics. The AlN emission is found to result primarily from the reaction of gas-phase nitrogen with vaporized aluminum.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
82.70.Kj Emulsions and suspensions
82.70.Rr Aerosols and foams
52.77.-j Plasma applications

Numerical study on microdischarges in plasma display panels with arbitrary cell geometry

Satoyuki Kawano and Takashi Misaka

J. Appl. Phys. 98, 053302 (2005); http://dx.doi.org/10.1063/1.2001145 (14 pages) | Cited 5 times

Online Publication Date: 7 September 2005

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In this study, a plasma display panel (PDP) cell is modeled in a two-dimensional cross-sectional region and plasma discharge characteristics are analyzed by numerical simulations based on the finite difference method developed here. An orthogonal curvilinear coordinate system is introduced to apply to the arbitrary PDP cell geometry for systematic computations. Wall voltage transfer curves derived through experiments and computation are compared in detail. They show good agreement. The effect of PDP cell geometry on the voltage margin and on ultraviolet (UV) photon production efficiency are also studied. Results show that the thickness of front dielectric layer has a marked effect on the voltage margin and UV photon production efficiency. Furthermore, the dielectric ribs prevent the crosstalk of discharge in two ways: they decrease a number of excited species leaking to adjacent PDP cells and decrease charge distribution on the dielectric surface near the cell boundaries.
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52.75.-d Plasma devices
52.80.-s Electric discharges
85.60.Pg Display systems

Modeling of microwave discharges of H2 admixed with CH4 for diamond deposition

G. Lombardi, K. Hassouni, G.-D. Stancu, L. Mechold, J. Röpcke, and A. Gicquel

J. Appl. Phys. 98, 053303 (2005); http://dx.doi.org/10.1063/1.2034646 (12 pages) | Cited 31 times

Online Publication Date: 12 September 2005

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Microwave discharges of H2 admixed with CH4 in a moderate-pressure quartz bell jar reactor used for diamond deposition are studied numerically. Special attention was devoted to high-power densities which provide the most effective way for producing high-quality diamond films. First, a one-dimensional radial model describing the coupled phenomena of chemistry, energy transfer, as well as species and energy transport along the reactor’s radial coordinate was developed. Species densities predicted with the model were compared with measurements with infrared tunable diode laser spectroscopy, resulting in validation of the model. Second, a one-dimensional axial model was used to describe the plasma flow along the reactor axis in a region between the reactor end wall and the substrate surface. This model was particularly useful for studying the plasma behavior in the vicinity of the substrate surface, where thermal and composition gradients are large. Both the radial and axial transport models are based on the same discharge model in which the plasma is described as a thermochemically nonequilibrium flow with different energy distributions for heavy species and electrons. The chemistry was described with a model containing 28 species and 131 reactions. The electron temperature, the gas temperature, and the species concentration were determined by solving a coupled set of equations. A wide range of experimental conditions used for diamond deposition was simulated, from low microwave power density (9 W cm−3, i.e., 600 W, 2500 Pa, and Tg ∼ 2200 K) to high-power density (30 W cm−3, i.e., 2 kW, 12 000 Pa, and Tg ∼ 3200 K). The main chemical paths were identified, and the major species, transport effects, and reaction pathways that govern diamond deposition plasmas are discussed.
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52.80.Pi High-frequency and RF discharges
52.77.Dq Plasma-based ion implantation and deposition
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.25.Fi Transport properties
52.30.-q Plasma dynamics and flow
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Kn Thermodynamics of plasmas
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Experimental and theoretical study of bulk light scattering in CaF2 monocrystals

Stephan Logunov and Sergey Kuchinsky

J. Appl. Phys. 98, 053501 (2005); http://dx.doi.org/10.1063/1.2034085 (7 pages) | Cited 4 times

Online Publication Date: 2 September 2005

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A variety of different types of light scattering (Rayleigh, Brillouin, Raman, and Mie scatterings), which may contribute to the transmission losses in the bulk of high-quality CaF2 monocrystals, have been investigated experimentally and theoretically. The angular distribution of Rayleigh and Mie scatterings in the visible spectral range has been measured using an imaging technique. An effective technique for scattering measurements in the uv spectral range has also been implemented. Measurement of Raman scattering has shown that its contribution to the total scattering loss is negligible. In order to estimate the scattering from thermal fluctuations versus that from crystalline defects, a measurement of the temperature dependence of the scattering at the scattering angle of 90° has been performed. It has been shown that scatterings from thermal fluctuations and defects are of the same order of magnitude. Taking into account the dependence of the Brillouin scattering on the direction of the incident beam relative to crystalline axes, an upper limit of scattering loss due to thermal fluctuation in the perfect crystal has been evaluated theoretically. At 193 nm this limit appeared to be 2.6×10−5 cm−1, which is about two orders of magnitude less than the scattering loss in fused silica. Measured values of Rayleigh and Mie scatterings are in reasonable agreement with theoretical evaluation. Scattering measured in high-quality samples are comparable with the scattering calculated from thermodynamic fluctuations, indicating that the transmission of these samples is approaching the theoretical limit.
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78.30.Hv Other nonmetallic inorganics
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.40.Ha Other nonmetallic inorganics
61.72.-y Defects and impurities in crystals; microstructure

Thermal stability of diamondlike carbon buried layer fabricated by plasma immersion ion implantation and deposition in silicon on insulator

Zengfeng Di, Anping Huang, Ricky K. Y. Fu, Paul K. Chu, Lin Shao, T. Höchbauer, M. Nastasi, Miao Zhang, Weili Liu, Qinwo Shen, Suhua Luo, Zhitang Song, and Chenglu Lin

J. Appl. Phys. 98, 053502 (2005); http://dx.doi.org/10.1063/1.2034651 (5 pages) | Cited 8 times

Online Publication Date: 2 September 2005

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Diamondlike carbon (DLC) as a potential low-cost substitute for diamond has been extended to microelectronics and we have demonstrated the fabrication of silicon on diamond (SOD) as a silicon-on-insulator structure using plasma immersion ion implantation and deposition in conjunction with layer transfer and wafer bonding. The thermal stability of our SOD structure was found to be better than that expected for conventional DLC films. In the work reported here, we investigate the mechanism of the enhanced thermal stability. We compare the thermal stability of exposed and buried DLC films using Raman spectroscopy and x-ray photoelectron spectroscopy (XPS). Our Raman analysis indicates that the obvious separation of the D and G peaks indicative of nanocrystalline graphite emerges at 500 °C in the exposed DLC film. In contrast, the separation appears in the buried DLC film only at annealing temperatures above 800 °C. Analysis of the XPS C1s core-level spectra shows that the (sp3+C–H) carbon content of the unprotected DLC film decreases rapidly between 300–700 °C indicating the rapid transformation of sp3-bonded carbon to sp2-bonded carbon combined with hydrogen evolution. In comparison, the decrease in the (sp3+C–H) carbon content of the buried DLC film is slower below 800 °C. Elastic recoil detection results show that this superior thermal stability is due to the slower hydrogen out diffusion from the buried DLC film thereby impeding the graphitization process. We propose that the SiO2 overlayer retards the graphitization process during annealing by shifting the chemical equilibrium.
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81.05.U- Carbon/carbon-based materials
68.60.Dv Thermal stability; thermal effects
52.77.Dq Plasma-based ion implantation and deposition
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.A- Nucleation and growth
61.72.up Other materials
78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
81.40.Gh Other heat and thermomechanical treatments

Role of S/Se ratio in chemical bonding of As–S–Se glasses investigated by Raman, x-ray photoelectron, and extended x-ray absorption fine structure spectroscopies

Wenyan Li, Sudipta Seal, Clara Rivero, Cedric Lopez, Kathleen Richardson, April Pope, Alfons Schulte, Satish Myneni, Himanshu Jain, Keisha Antoine, and Alfred C. Miller

J. Appl. Phys. 98, 053503 (2005); http://dx.doi.org/10.1063/1.2009815 (11 pages) | Cited 29 times

Online Publication Date: 2 September 2005

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Chalcogenide glasses have attracted considerable attention and found various applications due to their infrared transparency and other optical properties. The As–S–Se chalcogenide glass, with its large glass-formation domain and favorable nonlinear property, is a promising candidate system for tailoring important optical properties through modification of glass composition. In this context, a systematic study on ternary As–S–Se glass, chalcogen-rich versus well-studied stochiometric compositions, has been carried out using three different techniques: Raman spectroscopy, x-ray photoelectron spectroscopy, and extended x-ray absorption fine structure spectroscopy. These complementary techniques lead to a consistent understanding of the role of S/Se ratio in chalcogen-rich As–S–Se glasses, as compared to stochiometric composition, and to provide insight into the structural units (such as the mixed pyramidal units) and evidence for the existence of homopolar bonds (such as Se–Se, S–S, and Se–S), which are the possible structural origin of the high nonlinearity in these glasses.
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61.43.Fs Glasses
78.35.+c Brillouin and Rayleigh scattering; other light scattering
79.60.Ht Disordered structures
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
78.70.Dm X-ray absorption spectra

Relaxation of a strained quantum well at a cleaved surface. Part II: Effect of cubic symmetry

John H. Davies, Peter Offermans, and Paul M. Koenraad

J. Appl. Phys. 98, 053504 (2005); http://dx.doi.org/10.1063/1.2030415 (10 pages)

Online Publication Date: 2 September 2005

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In a previous paper [ J. H. Davies, D. M. Bruls, J. W. A. M. Vugs, and P. M. Koenraad, J. Appl. Phys. 91, 4171 (2002). Part I. ] we compared theory and experiment for the relaxation at a cleaved surface of a strained quantum well of InGaAs in GaAs. The measurements were taken with a scanning tunneling microscope and the analytic calculation used classical elastic theory for a linear, isotropic, homogeneous medium. Qualitative agreement was good but the theory gave only about 80% of the observed displacement. We have therefore extended the calculation to explore the effect of cubic symmetry and the orientation of the cleaved surface. The “strain suppression” method reduces the problem to the response of a half space to traction on its surface. We have calculated this for orthotropic symmetry, which includes the common orientations of orthorhombic, tetragonal, hexagonal, and cubic crystals. Anisotropy has no effect on the shape of the relaxed surface but the magnitude of relaxation changes. For cubic material there is no effect on the strain along the direction of growth if the cleaved surface is a {001} plane and a reduction of a few percent for a {011} plane, which is the case of experimental interest. The outward relaxation is reduced by about 20% due to cubic symmetry for a {001} plane because the shear stiffness of GaAs is higher than in the isotropic model, and is a further 10% smaller for a {011} plane. Thus the results for cubic symmetry lie further from the measurements than those calculated for isotropic material. Interfacial forces may contribute to this discrepancy but we suggest that nonlinear elasticity is probably responsible.
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81.07.St Quantum wells
68.65.Fg Quantum wells
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.D- Elasticity
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Molecular-beam epitaxy and characteristics of GaNyAs1−x−yBix

Wei Huang, Kunishige Oe, Gan Feng, and Masahiro Yoshimoto

J. Appl. Phys. 98, 053505 (2005); http://dx.doi.org/10.1063/1.2032618 (6 pages) | Cited 21 times

Online Publication Date: 2 September 2005

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GaNyAs1−x−yBix alloys were grown by molecular-beam epitaxy using solid Ga, Bi, and As sources and nitrogen radicals generated from nitrogen gas in rf plasma. Changing the growth temperature is found to be a convenient method for controlling the GaBi molar fraction in the alloy reproducibly. The photoluminescence (PL) spectra show that the PL peak energy of GaNyAs1−x−yBix alloy decreased with increasing GaBi and GaN molar fractions. The redshift coefficients of ∼ 62 meV/%Bi and ∼ 130 meV/%N at the PL peak energy of GaNyAs1−x−yBix were observed at room temperature. The temperature dependence of the PL peak energy in the temperature range of 150–300 K is much smaller than the temperature dependence of the band gap of InGaAsP. The temperature coefficients of GaAs1−xBix and GaNyAs1−x−yBix band gaps are governed by the GaBi molar fraction and they decrease with increasing GaBi molar fraction. GaNyAs1−x−yBix alloys with different PL peak energies and lattice matched to GaAs substrates were obtained. The photoluminescence peak energy was located at a predicted wavelength for the sample lattice matched to GaAs which was found to have the structure of Ga(N0.33Bi0.67)zAs1−z.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.20.Nr Semiconductor compounds
78.55.Cr III-V semiconductors

Optical and structural investigation of In1−xGaxP free-standing microrods

M. K. K. Nakaema, M. P. F. Godoy, M. J. S. P. Brasil, F. Iikawa, D. Silva, M. Sacilotti, J. Decobert, and G. Patriarche

J. Appl. Phys. 98, 053506 (2005); http://dx.doi.org/10.1063/1.2033150 (6 pages) | Cited 3 times

Online Publication Date: 2 September 2005

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We present a structural and optical characterization of scepterlike micrometer-sized free-standing structures, composed of a long InGaP rod with a metallic sphere on its top, grown on polycrystalline InP substrates. In contrast to the conventional vapor-liquid-solid growth method, no catalyst was deposited on the substrate. Instead, metallic In liberated from the InP substrate by phosphor evaporation works as the catalyst metal. We performed Raman scattering, photoluminescence spectroscopy, scanning electron microscopy, and energy dispersive x-ray spectroscopy measurements on individual structures. The alloy composition measured by microscopic techniques is in agreement with the values obtained by the optical measurements considering that the rod is strain free. The InGaP rods present essentially constant Ga composition within a fluctuation of ∼ 10% and efficient optical emission. We also observed a marked increase in the Raman-scattering signal at rod positions near the metallic sphere (the “neck”), which was attributed to a surface-enhanced Raman-scattering effect. Our results demonstrate the possibility of using InGaP rods for optical device applications.
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78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
61.46.-w Structure of nanoscale materials

Influence of germanium on the formation of NiSi1−xGex on (111)-oriented Si1−xGex

T. Jarmar, F. Ericson, U. Smith, J. Seger, and S.-L. Zhang

J. Appl. Phys. 98, 053507 (2005); http://dx.doi.org/10.1063/1.2034081 (9 pages) | Cited 1 time

Online Publication Date: 6 September 2005

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The formation of NiSi1−xGex on Si1−xGex(111) substrates with x = 0, 0.05, and 0.20 at an annealing temperature of 500 °C has been studied by x-ray diffraction, transmission electron microscopy, and pole-figure measurements. NiSi formed preferentially oriented on Si, with (100), (001), and (102) parallel to Si(111) and NiSi[010]‖Si〈211〉. In NiSi0.95Ge0.05, (001) and (102) maintained their preferential orientations, whereas NiSi0.95Ge0.05(100) was rotated by 30°, so that NiSi0.95Ge0.05[010]‖Si0.95Ge0.05〈011〉. An epitaxial alignment in the form of a double axiotaxy, with NiSi0.95Ge0.05(2±11) as well as (20−2)‖Si0.95Ge0.05{220}, simultaneously with NiSi0.95Ge0.05(0±13) as well as (020)‖Si0.95Ge0.05{022}, caused NiSi0.95Ge0.05(100) to tilt over the range of 0°–7.5°. The Ge addition also enhanced the preferentially oriented structure by reinforcing NiSi0.95Ge0.05(123)‖Si0.95Ge0.05(111) through the axiotaxial alignments, NiSi0.95Ge0.05(211) and (−112)‖Si0.95Ge0.05{220}. Observed was also the presence of NiSi0.95Ge0.05(011)‖Si0.95Ge0.05(111), with NiSi0.95Ge0.05[100]‖Si0.95Ge0.05〈011〉. In the case of NiSi0.80Ge0.20, the preferential orientations were sharply reduced in favor of NiSi0.80Ge0.20(100)‖Si0.80Ge0.20(111), with NiSi0.80Ge0.20[010]‖Si0.80Ge0.20〈011〉 and the 30° rotation thus preserved. The observed Ge influence is shown to be consistent with a model suggested earlier for Si1−xGex(001) substrates, which is based on the nonexistence of Ni(Si1−xGex)2 for all except the smallest values of x. High-resolution transmission electron microscopy was used to show that the surface steps typical of molecular-beam-deposited epitaxial Si1−xGex substrate films do not influence the growth of the NiSi1−xGex.
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81.05.Bx Metals, semimetals, and alloys
68.55.A- Nucleation and growth
81.40.Gh Other heat and thermomechanical treatments
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.37.Lp Transmission electron microscopy (TEM)

Brillouin scattering study on the single-crystal elastic properties of natrolite and analcime zeolites

Carmen Sanchez-Valle, Stanislav V. Sinogeikin, Zoe A. D. Lethbridge, Richard I. Walton, Christopher W. Smith, Kenneth E. Evans, and Jay D. Bass

J. Appl. Phys. 98, 053508 (2005); http://dx.doi.org/10.1063/1.2014932 (6 pages) | Cited 22 times

Online Publication Date: 6 September 2005

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The Brillouin light-scattering technique was used to investigate the single-crystal elastic properties of two aluminosilicate zeolites, natrolite (NAT) and analcime (ANA), at ambient conditions. An inversion of the acoustic velocity data results in the full set of elastic stiffness moduli (Cij’s) for both materials. From the single-crystal moduli the aggregate adiabatic bulk moduli (Ks), shear moduli (G), and Poisson’s ratios (ν) were found to be Ks = 48.5(1.0) GPa, G = 31.6(1.0) GPa, and ν = 0.232(5) for NAT, and Ks = 59.8(1.2) GPa, G = 32.1(1.0) GPa, and ν = 0.272(5) for ANA (Voigt-Reuss-Hill averages). The bulk and shear moduli of both zeolites are relatively low compared with those of densely packed aluminosilicates, reflecting an open framework structure of (Al,SiO4) tetrahedra which is easily deformed by bending the Si–O–Al angles. As expected for a less dense crystal, NAT is softer and more compressible than ANA. An evaluation of the directional Young’s moduli shows that the compressibility of NAT is nearly uniform along the [100] and [010] axes, while [001] is stiffer, in agreement with previous compression studies. We do not find experimental evidence of negative Poisson’s ratios for NAT zeolites as predicted by recent theoretical calculations.
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82.75.-z Molecular sieves, zeolites, clathrates, and other complex solids
78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.F- Deformation and plasticity
62.65.+k Acoustical properties of solids

Determination of relative internal quantum efficiency in InGaN/GaN quantum wells

C. E. Martinez, N. M. Stanton, A. J. Kent, D. M. Graham, P. Dawson, M. J. Kappers, and C. J. Humphreys

J. Appl. Phys. 98, 053509 (2005); http://dx.doi.org/10.1063/1.2033144 (5 pages) | Cited 9 times

Online Publication Date: 6 September 2005

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We have investigated the relative quantum efficiency in a series of InGaN/GaN single quantum wells with differing indium concentration. The results of measurements involving direct detection of phonons emitted as a result of nonradiative recombination and carrier energy relaxation are compared with time-resolved photoluminescence studies. Using these complementary techniques we have extracted the low-temperature internal quantum efficiency of the recombination and observed the effect of free-carrier screening on the radiative and nonradiative processes in the quantum well samples. All the samples exhibit high quantum efficiency, with the maximum being observed in the 10% indium sample. In addition, we observe the appearance of a delayed phonon signal, which we correlate to the measured quantum efficiency of the samples.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Size-dependent change in interband absorption and broadening of optical plasma-resonance absorption of indium particles

E. Anno and M. Tanimoto

J. Appl. Phys. 98, 053510 (2005); http://dx.doi.org/10.1063/1.2033151 (7 pages) | Cited 4 times

Online Publication Date: 6 September 2005

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Optical absorption of indium-island films, consisting of indium particles smaller than about 500 Å in diameter, has been investigated experimentally. The interband absorption, the position of which is almost constant (at about 234 nm) irrespective of particle size, was found to disappear in particle sizes below about 200 Å in diameter. This disappearance is pointed out to be similar to that in lead particles, where the disappearance is due to the effect of surface atoms. Optical plasma-resonance absorption appeared at 276–335 nm. By simulating this absorption with a Maxwell-Garnett-type effective-medium theory, we investigated the relaxation time τ and the mean free path l of conduction electrons. τ and l for particle sizes of about 120 and 160 Å in diameter are estimated to be (3.33–3.36)×10−16 s and 5.79–5.85 Å, respectively, which is smaller than the bulk values (0.38×10−14 s and 66.1 Å). The small τ and l are attributed to the scattering of the conduction electrons at lattice defects internal to the particles.
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78.66.Bz Metals and metallic alloys
72.15.Lh Relaxation times and mean free paths
73.61.At Metal and metallic alloys
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.40.Kc Metals, semimetals, and alloys
61.72.-y Defects and impurities in crystals; microstructure

Diffusion in interstitial compounds with thermal and stoichiometric defects

Mats Hillert, Lars Höglund, and John Ågren

J. Appl. Phys. 98, 053511 (2005); http://dx.doi.org/10.1063/1.1999833 (6 pages) | Cited 10 times

Online Publication Date: 7 September 2005

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The ordinary flux equation for diffusion, which considers the composition gradient as the driving force, is seldom of much use in studying closely stoichiometric phases. Depending on the defect structure it would instead be profitable to use an appropriate function of the activity. Such functions will now be derived and it will be shown how the operating defect mechanism of diffusion can be identified from information on the variation of the activity inside a phase during diffusion. However, it is usually very difficult to measure the activity profile inside a phase. It will be shown how it can be obtained by combining results from several experiments. The method will be used to analyze experimental information on the formation of surface layers of Fe4N and Fe3C.
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66.30.Dn Theory of diffusion and ionic conduction in solids
66.30.H- Self-diffusion and ionic conduction in nonmetals
61.72.J- Point defects and defect clusters
61.66.Bi Elemental solids
61.66.Dk Alloys

Room-temperature defect tolerance of band-engineered InAs quantum dot heterostructures

S. Oktyabrsky, M. Lamberti, V. Tokranov, G. Agnello, and M. Yakimov

J. Appl. Phys. 98, 053512 (2005); http://dx.doi.org/10.1063/1.2037872 (8 pages) | Cited 5 times

Online Publication Date: 7 September 2005

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Using photoluminescence (PL) at 77–420 K and high-energy proton implantation (1.5 MeV, dose up to 3×1014 cm−2) we have studied the thermal quenching of PL and defect tolerance of self-assembled shape-engineered InAs quantum dots (QDs) embedded into GaAs quantum wells (QWs). At room temperature, QDs appeared to withstand two orders of magnitude higher proton doses than QWs without PL degradation. A simple dynamic model was used to account for both dose and temperature dependence of PL efficiency. At low temperatures, the defect-related quenching is mainly controlled by a reduction in the density of defect-free QDs. At and above room temperature, both thermal and defect-related quenching of PL are due to the escape of carriers from dots to wells that act as barriers with low damage constants. A relatively large barrier for escape (450 meV) as well as low nonradiative recombination rate in QDs is shown to account for unsurpassed room-temperature defect tolerance and high PL efficiency at room and elevated temperatures.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
81.07.St Quantum wells
78.67.Hc Quantum dots
78.67.De Quantum wells
78.55.Cr III-V semiconductors
73.21.La Quantum dots
71.20.Nr Semiconductor compounds
61.72.J- Point defects and defect clusters
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
81.40.Gh Other heat and thermomechanical treatments

Defect dynamics in annealed ZnO by positron annihilation spectroscopy

Sreetama Dutta, Mahuya Chakrabarti, S. Chattopadhyay, Debnarayan Jana, D. Sanyal, and A. Sarkar

J. Appl. Phys. 98, 053513 (2005); http://dx.doi.org/10.1063/1.2035308 (5 pages) | Cited 21 times

Online Publication Date: 13 September 2005

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As-supplied polycrystalline ZnO samples (purity 99.9% from Sigma-Aldrich, Germany) have been annealed at different temperatures and subsequently characterized by positron annihilation spectroscopy, x-ray-diffraction (XRD) analysis, thermogravimetric analysis (TGA), and resistivity measurements. Positron annihilation lifetime analysis and coincidence Doppler-broadened electron-positron annihilation γ-radiation (CDBEPAR) line-shape measurements have been employed at a time to identify the nature of defects in differently annealed ZnO materials. Annealing up to 300 °C, an increase of defect lifetime (τ2) as well as shape parameter (S parameter) has been observed. Further annealing causes a large decrease of τ2 and S parameter. TGA study shows considerable mass loss from ZnO as the annealing temperature is increased above 300 °C. This is possibly due to oxygen evaporation from the sample. The c-axis lattice parameter, extracted from the XRD spectra, shows an increase due to annealing above 600 °C, which is a signature of the presence of a huge number of oxygen vacancies. Resistivity variations of the annealed samples are also consistent with the TG and XRD analyses. The ratio curve analysis of the CDBEPAR spectra successfully probes the change in zinc-related vacancy defects in annealed ZnO.
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61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
78.70.Bj Positron annihilation

Equation of state and reaction rate for condensed-phase explosives

B. L. Wescott, D. Scott Stewart, and W. C. Davis

J. Appl. Phys. 98, 053514 (2005); http://dx.doi.org/10.1063/1.2035310 (10 pages) | Cited 3 times

Online Publication Date: 8 September 2005

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The wide-ranging equation of state is a nonideal equation of state based on empirical fitting forms argued from thermodynamic considerations that yield the proper physical features of detonation. The complete equation of state forms are presented and the equation of state and a reaction rate are calibrated for the condensed-phase explosive PBX-9502. Experimental overdriven Hugoniot data are used to calibrate the products equation of state off the principal isentrope passing through the Chapman-Jouguet state. Shock Hugoniot data are used to calibrate the reactants equation of state. The normal detonation shock speed-shock curvature data (Dn−κ) from rate-stick measurements and shock initiation data from wedge tests are used to calibrate the reaction rate. Simulations are carried out that predict detailed particle velocity transients that are measured experimentally with embedded electromagnetic gauge measurements from gas-gun experiments. Multidimensional simulations of steady detonation in a right circular cylinder rate stick are carried out and compared with experiment.
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82.33.Vx Reactions in flames, combustion, and explosions
64.10.+h General theory of equations of state and phase equilibria
47.40.-x Compressible flows; shock waves
64.30.-t Equations of state of specific substances

Tailoring of high-temperature photoluminescence in InAs/GaAs bilayer quantum dot structures

Yu. I. Mazur, Zh. M. Wang, G. G. Tarasov, Vas. P. Kunets, G. J. Salamo, Z. Ya. Zhuchenko, and H. Kissel

J. Appl. Phys. 98, 053515 (2005); http://dx.doi.org/10.1063/1.2039271 (6 pages) | Cited 7 times

Online Publication Date: 8 September 2005

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Temperature-dependent photoluminescence is investigated in bilayer InAs/GaAs quantum dot structures with constant InAs deposition θ1 in the seed layer, but variable deposition θ2 in both the second layer and the GaAs spacer layer. It is shown that interlayer coupling, leading to the formation of asymmetric quantum dot pairs, strengthens the high-temperature photoluminescence and strongly influences carrier relaxation channels. We report that radiative recombination and carrier capture efficiency by the quantum dots in the second layer can be tailored using the deposition θ2 and the GaAs spacer thickness.
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78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.63.Kv Quantum dots

Error analyses on some typically approximate solutions of residual stress within a thin film on a substrate

X. C. Zhang, B. S. Xu, H. D. Wang, and Y. X. WU

J. Appl. Phys. 98, 053516 (2005); http://dx.doi.org/10.1063/1.2039277 (5 pages) | Cited 9 times

Online Publication Date: 9 September 2005

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Stoney's equation and subsequent modifications and some approximations are widely used to evaluate the macrostress within a film on a substrate, though some of these solutions are only applicable for thin films. The purpose of this paper is to review the considerable efforts devoted to the analysis of residual stresses in a single-layer film in the last century and recent years and to estimate the errors involved in using these formulas. The following are some of the important results that can be obtained. (1) The exact solution for the residual stress can be expressed in terms of Stoney's equation [Proc. R. Soc. London A82, 172 (1909)] and a correction factor, (1+Ση3)/(1+η), where Σ,η are the ratios of the elastic modulus and the thickness of the film to those of the substrate, respectively. (2) When the thickness ratio of the film and the substrate is less than 0.1, Stoney's equation and Röll's approximation [J. Appl. Phys. 47, 3224 (1976)] do not cause serious errors. (3) The approximation proposed by Vilms and Kerps [J. Appl. Phys. 53, 1536 (1982)] is an improved modification for Stoney's equation and can be applicable when η ≤ 0.3. (4) The approximations proposed by Brenner and Senderoff [J. Res. Natl. Bur. Stand. 42, 105 (1949)] and Teixeira [Thin Solid Films 392, 276 (2001)] can lead to serious errors and should be avoided. (5) The approximation based on the assumption of constant elastic modulus is only applicable for a ratio of η ≤ 0.01 and can be very misleading.
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68.60.Bs Mechanical and acoustical properties
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
06.20.Dk Measurement and error theory

Simple theory of the interband optical absorption in an external electric field for optoelectronic materials

P. K. Chakraborty, S. Bhattacharya, and K. P. Ghatak

J. Appl. Phys. 98, 053517 (2005); http://dx.doi.org/10.1063/1.2040003 (10 pages) | Cited 4 times

Online Publication Date: 12 September 2005

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We study theoretically the interband optical-absorption coefficient (OAC) of optoelectronic materials within the framework of the three-band model of Kane [J. Phys. Chem. Solids 12, 181 (1959) ] in the presence of an external electric field for modified photon energy (ℏω1) below and above the band gap (Eg), respectively. The optical matrix element depends on the electron wave vector k and this practical aspect has been incorporated in the present analysis. It has been found, taking InAs, InSb, Hg1−xCdxTe, and In1−xGaxAsyP1−y lattice matched to InP as examples of optoelectronic compounds for numerical computations, that for modified photon energies below the band gap, the OAC exhibits an exponential fall off with the electric field and the photon energy, respectively. For the opposite inequality, the OAC oscillates with the modified photon energy without the consideration of the Wannier-Stark levels, which generally exist in a band due to the presence of an external electric field. In both cases, the OAC exhibits the singularity when the incident photon energy (ℏω0) tends to Eg and the magnitude of the OAC depends to a large extent on the numerical values of the energy-band constants of the said compounds. In addition, the simplified results of the OAC for materials having parabolic energy bands have also been obtained from the present generalized analysis under certain limiting conditions.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds

Metal-organic molecular-beam epitaxy of GaN with trimethylgallium and ammonia: Experiment and modeling

I. Gherasoiu, S. Nikishin, and H. Temkin

J. Appl. Phys. 98, 053518 (2005); http://dx.doi.org/10.1063/1.2039276 (5 pages)

Online Publication Date: 13 September 2005

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Metal-organic molecular-beam epitaxy with trimethylgallium and ammonia is used to grow GaN on Si(111). Our analysis of the growth data shows an increase in the apparent formation energy Eapp of epitaxial GaN, from 0.168 to 0.56 eV, with an increasing flux of ammonia. A rate-equation-based growth model is proposed and used to fit the growth data. Regarding the interaction potential, the model assumes the presence of an activated state, intermediate between physisorption and chemisorption, and includes second-order recombination-desorption processes important in the modeling of high-temperature growth. It is shown that the formation energy of epitaxial GaN, Ef, depends on the growth conditions as the activation energy and surface diffusion energy barriers increase or decrease with the change in the impinging fluxes and surface density of precursors. For such a particular set of growth conditions, the model allows us to determine the formation energy of epitaxial GaN as Ef = 0.11 eV, ∼ 35% smaller than the apparent activation energy obtained directly from the growth data. Eapp = 0.168 eV.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
68.35.Fx Diffusion; interface formation
68.35.Md Surface thermodynamics, surface energies
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation

Nonlinear dynamics in Tomlinson’s model for atomic-scale friction and friction force microscopy

W. G. Conley, A. Raman, and C. M. Krousgrill

J. Appl. Phys. 98, 053519 (2005); http://dx.doi.org/10.1063/1.2037207 (10 pages) | Cited 5 times

Online Publication Date: 15 September 2005

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Tomlinson’s model is often used to describe the friction of a single asperity or of a scanning force probe sliding over an atomic lattice. We present results on the complex dynamic behavior found in this model using a combination of continuation methods, perturbation techniques, and numerical simulations. Specifically, periodic stick-slip motions and their bifurcations and stability are investigated in the slow-sliding speed range and in higher speed ranges at which fundamental and parametric resonances set in. The results predict a complex range of bifurcations, superharmonic and subharmonic motions, and possibly chaotic dynamics which bear significant implications for understanding single-asperity friction or the dynamic response in friction force microscopy.
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07.79.Sp Friction force microscopes
05.45.-a Nonlinear dynamics and chaos
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Comprehensive study of Ohmic electrical characteristics and optimization of Ti/Al/Mo/Au multilayer Ohmics on undoped AlGaN/GaN heterostructure

Yunju Sun, Xiaodong Chen, and L. F. Eastman

J. Appl. Phys. 98, 053701 (2005); http://dx.doi.org/10.1063/1.2035314 (5 pages) | Cited 5 times

Online Publication Date: 6 September 2005

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The performance of Ohmic contacts is highly dependent on the metal stack contents and layer thicknesses evaporated, annealing temperature, and annealing time. A four-layer-based metal stack was used to form Ohmic contacts on an undoped AlGaN/GaN material structure, grown by molecular-beam epitaxy technique on a sapphire substrate. The thicknesses of the overlayers Ti/Au, or Mo/Au, investigated were fixed. The rapid thermal annealing time and temperature in a N2 ambient are optimized for Ti/Al/Mo/Au (from bottom to top) metal stack system, with bottom Ti/Al metal at thickness ratios of 1:5 and 1:6. The lowest contact transfer resistance rt of 0.4 Ω mm was obtained for Ti/Al metal at thickness ratio of 1:5. The sheet resistance Rsh associated with it was 600 Ω/sq. The edge acuity of Ti/Al/Mo/Au Ohmic contacts after annealing has been discussed and examined under scanning electron microscopy for the optimized Ohmic contact transfer resistance associated with the bottom Ti/Al metal at thickness ratios of 1:5 and 1:6. The straightness of the edge of the metal contact has also been compared with the one using Ti/Al/Ti/Au as the Ohmic metal stack under the condition of same annealing environment and metal thickness.
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73.40.Ns Metal-nonmetal contacts
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Cg Contact resistance, contact potential
61.72.Cc Kinetics of defect formation and annealing
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