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Journal of Applied Physics

Issue 3 • Date Aug 2004

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Displaying Results 1 - 25 of 81
  • Issue Cover

    Page(s): c1
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  • Issue Table of Contents

    Page(s): toc1
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  • Effect of constituent phases of reactively sputtered AgOx film on recording and readout mechanisms of super-resolution near-field structure disk

    Page(s): 1283 - 1288
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    We have studied the dependence of the constituent phases of reactively sputtered AgOx mask layer on the recording and readout mechanisms of super-resolution near-field disk. At low oxygen flow ratios, the AgOx mask layer was found to be composed of an appreciable amount of Ag particles with sizes of tens of nanometers and Ag2O phase. After recording by a high power laser pulse, a hollow Ag cylinder that had its center filled with O2 was formed in the AgOx mask layer. The hollow Ag cylinder would serve as an aperture and could effectively reduce the laser spot size during readout, leading to the super-resolution effect only. At high oxygen flow ratios, the AgOx mask layer was found to be mostly composed of Ag2O and/or AgO phases. After recording by a high power laser pulse, a hollow Ag cylinder that had its center filled with nanosized Ag particles was formed in the AgOx mask layer. The nanosized Ag precipitates would serve as light-scattering centers and could yield strong near-field interaction with the subwavelength marks, resulting in both the super-resolution and near-field effects during readout. View full abstract»

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  • Ultralow-threshold cryogenic vertical-cavity surface-emitting laser with AlAs oxideGaAs distributed Bragg reflectors

    Page(s): 1289 - 1292
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    Data are presented on vertical-cavity surface-emitting lasers designed for cryogenic operation. Low-loss cavity design and high quality factor of the cavity provide the superior lasing characteristics at T=80 K. Ultralow lasing threshold current of 15 μA with external differential quantum efficiency 26% is achieved for a 5 μm aperture device, and a 31% efficiency is achieved for a 8 μm aperture device with a 30 μA threshold and 47 A/cm2 threshold current density. View full abstract»

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  • Near-field enhancement and imaging in double planar polariton-resonant structures

    Page(s): 1293 - 1300
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    It is shown that a system of two coupled planar material sheets possessing surface mode (polariton) resonances can be used for the purpose of evanescent field restoration and, thus, for sub-wavelength near-field imaging. The sheets are placed in free space so that they are parallel and separated by a certain distance. Due to interaction of the resonating surface modes (polaritons) of the sheets an exponential growth in the amplitude of an evanescent plane wave in the system can be achieved. This effect was predicted earlier for backward-wave (double-negative or Veselago) slab lenses. The alternative system considered here is proved to be realizable at microwaves by grids or arrays of resonant particles. The necessary electromagnetic properties of the resonating grids and the particles are investigated and established. Theoretical results are supported by microwave experiments that demonstrate amplification of evanescent modes. View full abstract»

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  • Hydrogen emission by Nd-YAG laser-induced shock wave plasma and its application to the quantitative analysis of zircalloy

    Page(s): 1301 - 1309
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    An experiment was carried out to demonstrate the detection of a hydrogen emission line, H I 656.2 nm (Hα), in a plasma induced by a Q-switched Nd-YAG (YAG, yttrium aluminium garnet) laser in a low pressure gas on various types of samples, such as zinc, a glass slide, and a zircalloy tube. Contribution by surface water could be suppressed by a laser cleaning treatment and the resulting calibration curve obtained for zircalloy tube samples doped with various concentrations of hydrogen (0, 200, 540, and 960 ) suggest potential applications to the quantitative analysis of hydrogen. A study of the dynamic process represented by the time profiles of the hydrogen emission, in comparison with those for zinc atomic emission, revealed a specific feature that is related to the small mass of hydrogen. This specific feature can be explained by the shock wave excitation mechanism in terms of new hypothetical process, namely, a mismatch between the movement of ablated hydrogen atoms and the formation of the shock wave. View full abstract»

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  • Electron transport in the downstream region of planar unbalanced magnetron discharge

    Page(s): 1310 - 1317
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    In this study, we will investigate the electron transport in the downstream region of a planar and unbalanced (type II) magnetron discharge. The effects of the anode sheath boundary and diverging magnetic field on the electron kinetics such as the electron loss mechanism at plasma-sheath boundary and the electron distribution function will be examined through the probe measurements. The spatially resolved probe measurements reveal the existence of an electron drift from the cathode fall region to the downstream region. It is found that this drift is caused by the axial gradient of magnetic field (the magnetic mirror force) and then derives an electron current to the grounded substrate on which the potential of the sheath is very low; so the current balance between the cathode and anode currents is kept. The experimental results show that the electron transport in the downstream region is not governed by the classical diffusion (mobility and diffusion dominated) but is dominated by the modified diffusion including the electron drift caused by the magnetic mirror force. Additionally, the mechanism and the experimental evidence on the presence of a non-Maxwellian electron energy distribution function (in particular, bi-Maxwellian distribution) in magnetron discharge will be presented showing that the non-Maxwellian electron energy distribution function is due to the combined effects of the electron drift toward the substrate and the sheath boundary condition. View full abstract»

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  • Statistical geometry of random fibrous networks, revisited: Waviness, dimensionality, and percolation

    Page(s): 1318 - 1327
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    Waviness alters both geometric and mechanical properties of stochastic fibrous networks and significantly affects overall mechanical response, but few results are available in the literature on the subject. In this work, we explore the importance of the dimension of constituent fibers (1D vs 2D) in determination of percolation thresholds, and other fundamental statistical properties of fibers having geometric waviness, in adaptation of classical theories on random lattices to practical applications, including analysis of nanotube ropes and collagen bundles. Although the so-called “curl ratio” clearly affects the statistical properties, as evaluated by Kallmes and Corte a few decades ago, we have found some results in this classic work to be inaccurate for systems containing fibers of moderate waviness. Our main findings include the independence of the mean number of crossings with regard to waviness, as well as the nonlinear dependence of probability of intersection on waviness. Our investigation of percolation in wavy fiber networks reveals that the percolation threshold is significantly increased, with increasing curl ratio. In addition, several nontrivial results related to network properties of infinite straight lines are also described, some of which are believed to have wide applications in practice. © 2004 American Institute of Physics. View full abstract»

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  • Damage accumulation in Si during high-dose self-ion implantation

    Page(s): 1328 - 1335
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    Accumulation and annealing of damage in Si implanted with self-ions to high doses were investigated using a combination of grazing incidence diffuse x-ray scattering, high-resolution x-ray diffraction scans, and transmission electron microscopy. During implantation at 100°C, small vacancy and interstitial clusters formed at low doses, but their concentrations saturated after a dose of ≈3×1014 cm-2. The concentration of Frenkel defects at this stage of the implantation was ≈1×10-3. At doses above 1×1015 cm-2, the concentration of implanted interstitial atoms began to exceed the Frenkel pair concentration, causing the interstitial clusters to grow, and by ≈3×1015 cm-2, these clusters formed dislocation loops. Kinematical analysis of the rocking curves illustrated that at doses above 1×1015 cm-2 the “plus one” model was well obeyed, with one interstitial atom being added to the dislocation loops for every implanted Si atom. Measurements of Huang scattering during isochronal annealing showed that annealing was substantial below 700°C for the specimens irradiated to lower doses, but that little annealing occurred in the other samples owing to the large imbalance between interstitial and vacancy defects. Between 700 and 900°C a large increase in the size of the interstitial clusters was observed, particularly in the low-dose samples. Above 900°C, the interstitial clusters annealed. View full abstract»

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  • Effects of ultrastrong gravitational field on the crystalline state of a Bi-Sb alloy

    Page(s): 1336 - 1340
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    An atomic-scale graded structure has been formed previously in a Bi70Sb30 (at. %) alloy that is miscible in all proportions, by sedimentation of substitutional solute atoms under an ultrastrong gravitational field up to 1×106G at 220–240 °C [T. Mashimo, T. Ikeda, and I. Minato, J. Appl. Phys. 90, 741 (2001)]. In this study, additional megagravity field experiments were performed on the Bi70Sb30 alloy and pure Bi at different temperatures below their melting points, to investigate the change in crystalline state under the ultrastrong gravitational field. For the Bi70Sb30 alloy ultracentrifuged at 191–205 °C, no change in composition was observed, and the grain sizes of the crystals decreased from several millimeters to tens of micrometers, while no distinct change in grain size was observed for the pure Bi ultracentrifuged under the same experimental conditions. The Bi70Sb30 alloy ultracentrifuged at 220–240 °C consisted of two regions with different morphologies–fine-grained crystals with grain sizes in the range of tens of micrometers in the low gravity region, and large crystals with grain sizes several millimeters long and hundreds of micrometers wide along the direction of gravity in the high gravity region, where sedimentation of atoms was confirmed. The large crystals with hexagonal structures were formed by preferential crystal growth roughly along the c axes, and a large strain that increased as the gravitational field increased existed inside these crystals. Formation of this anomalous crystal state might be correlated with the sedimentati- on of atoms. © 2004 American Institute of Physics. View full abstract»

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  • Assignment of deep levels causing yellow luminescence in GaN

    Page(s): 1341 - 1347
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    The deep levels in GaN associated with yellow luminescence transitions have been investigated using photoluminescence, Hall measurements, and deep level transient spectroscopy (DLTS). Hall measurements on Si-doped GaN show the presence of donor levels at ∼18, ∼35, and ∼70 meV, which are respectively associated with the Si shallow donors, O impurities, and the nitrogen vacancies (VN). DLTS measurements, on the other hand, reveal trap levels at Ec-0.1 eV, Ec-(0.2–0.24) eV, and Ev+0.87 eV. The trap level at Ec-0.1 eV obtained from DLTS can be correlated to the 70 meV deep donor (VN) obtained from Hall measurements. The deep donor band at Ec-(0.2–0.24) eV is attributed to the ON related defect complex decorated along dislocation sites while the hole level at Ev+0.87 eV is attributed to the Ga vacancy (VGa). Thermal annealing at 750 °C in nitrogen ambient results in reduction of yellow luminescence, which could be due to decrease in the concentration of VN and ON-related defect complexes. From these observations, we propose that yellow luminescence in GaN arises from the transitions from the Ec-(0.2–0.24) eV levels to the deep level at Ev+0.87 eV. © 2004 American Institute of Physics. View full abstract»

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  • Crystallite coalescence during film growth based on improved contact mechanics adhesion models

    Page(s): 1348 - 1359
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    Intrinsic tensile stress, which can lead to problems in deposited thin films such as cracking, peeling, and delamination, often develops during the early stages of thin film growth. Many attempts have been made to estimate the tensile stress during crystallite coalescence, both experimentally and analytically. Most recently, using a combination of Hertzian contact mechanics and elasticity theory, Freund and Chason applied the Johnson-Kendall-Roberts (JKR) theory to account for adhesion between crystallites under specific conditions. Other existing contact mechanics models that naturally account for adhesion include the improved Derjaguin-Muller-Toporotov and Maugis-Dugdale theories. The objective of this study is to provide useful analytical and numerical techniques based on these contact mechanics theories for a wide range of conditions that accurately approximate the intrinsic tensile stress that develops during crystallite coalescence. As an analytical method, the Maugis-Dugdale model is proposed as a more general alternative to the JKR model. Parameters such as the contact radius and “net” adhesive force are computed as a function of the relative separation between two adjacent crystallites in a thin gold film. Another useful parameter known as the “jump-to-contact” separation is also calculated by the Maugis-Dugdale and JKR models. For comparison to the analytical models, a finite element method is used to simulate the crystallite coalescence problem. The numerical technique is based on a nonlinear surface interaction element developed to approximate van der Waals adhesion, and allows for full-field analysis of stress and displacement in crystallites. Two different boundary conditions are used, for which corresponding contact radius and tensile stress are computed and compared to the analytical results. As a further study, the length scale effect is also investigated by varying the radius of individual crystallites from 20 nm to 300 nm. It is concluded that in order to estimate the average tensile stress accurately using analytical models, the radius of individual crystallites must be large compared to the contact radius. For small length scales, the finite element approach is more appropriate. View full abstract»

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  • Up-conversion in Er3+:Y2O3 Nanocrystals Pumped at 808 nm

    Page(s): 1360 - 1364
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    Er3+ ion-doped Y2O3 nanocrystals were prepared by coprecipitation synthesis technique. Visible emissions at 650, 540, and 523 nm have been observed under excitation at 808 nm. Comparing with the stokes emission characteristics of the nanocrystals pumped at 488 nm, the up-conversion mechanisms excited at 808 nm have been investigated in detail. Excitation power dependent behaviors of the up-converted emission intensities indicate that a two-photon excited state absorption process is responsible for the 4S3/2(2H11/2)→4I15/2 transition while a no-resonant energy transfer 4I9/2+4I11/24I9/2+4I13/2 principally performs the red up-conversion of the 4F9/24I15/2 transition. View full abstract»

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  • Effect of growth temperature and postmetallization annealing on the interface and dielectric quality of atomic layer deposited HfO2 on p and n silicon

    Page(s): 1365 - 1372
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    The effect of growth temperature and postmetallization annealing on the electrical characteristics of atomic layer deposited HfO2 films has been studied. Trap distributions at the interface have been obtained by means of deep level transient spectroscopy, whereas conductance transient technique provided the energy and geometrical profiles of electrically active defects at the insulator bulk. Differences in the interface quality have been observed between films on n- and p-type substrates. The most suitable growth temperatures seem to be 300 °C for p-type and 500 °C for n-type substrates. In all cases, postmetallization annealing in forming gas causes displacements of defects from the insulator bulk to the interface. View full abstract»

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  • Wavelength control of 1.3–1.6μm light emission from the quantum dots self-formed in GaAs/InAs short-period superlattices grown on InP (411)A substrates

    Page(s): 1373 - 1375
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    High lateral density quantum dot (QD) structures are self-formed by growing GaAs/InAs short-period superlattices (SLs) on InP (411)A substrates by gas source molecular beam epitaxy. Multilayer QD structures sandwiched with InP barrier layers showed a strong photoluminescence emission. The 1.3–1.6 μm wavelength emission was easily obtained and precisely controlled by regulating the SL period as well as the number of InAs monolayers (layer thickness). This wavelength control can be understood by considering the carrier confinement along the growth direction as well as the effective well depth change. View full abstract»

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  • Diffusion of boron in germanium at 800–900°C

    Page(s): 1376 - 1380
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    Diffusion of B in Ge is studied in the temperature range 800–900 °C using implantation doping and B doped epitaxial Ge layers. Concentration profiles before and after furnace annealing were obtained using high resolution secondary ion mass spectroscopy (SIMS). Diffusion coefficients were calculated by fitting the annealed profiles using TSUPREM. We obtained diffusivity values which are at least two orders of magnitude lower than the lowest values previously reported in the literature. Using our values an activation energy of 4.65(±0.3) eV is calculated. Present experimental results suggest that interstitial mediated mechanism should be considered for B diffusion in Ge in accordance with recent theoretical calculations. Annealed SIMS profiles also suggest that B solid solubility in Ge is ∼2×1018 cm-3 at 875 °C which agrees with literature values. View full abstract»

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  • Effect of gallium nitride template layer strain on the growth of InxGa1-xN/GaN multiple quantum well light emitting diodes

    Page(s): 1381 - 1386
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    GaN template layer strain effects on the growth of InGaN/GaN light emitting diodes devices were investigated. Seven-period InGaN/GaN multiple quantum well structures (MQW) were deposited on 5 and 15 μm GaN template layers. It was found that the electroluminescence emission of the 15 μm device was redshifted by approximately 132 meV. Triple-axis x-ray diffraction and cross-sectional transmission electron microscopy show that the 15 μm template layer device was virtually unstrained while the 5 μm layer experienced tensile strain. Dynamic secondary ion mass spectrometry depth profiles show that the 15 μm template layer device had an average indium concentration of 11% higher than that of the 5 μm template layer device even though the MQW structures were deposited during the same growth run. It was also found that the 15 μm layer device had a higher average growth rate than the 5 μm template layer device. This difference in indium concentration and growth rate was due to changes in thermodynamic limitations caused by strain differences in the template layers. View full abstract»

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  • Optical properties of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals studied by spectroscopic ellipsometry

    Page(s): 1387 - 1391
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    (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-x PT) single crystals with x=0.24, 0.30, 0.31, and 0.33 have been investigated by spectroscopic ellipsometry. The refractive indices and extinction coefficients were obtained. The modified Sellmeier equations for the refractive indices were obtained by least-squares fit. The equations can be used to calculate the refractive index with high accuracy in the low absorption wavelength range, namely, from 400 to 5800 nm. The Sellmeier optical coefficients E0, λ0, S0, and Ed were calculated by fitting the single-term oscillator equation. They are related directly to the electronic energy band structure and have the physical significance. The optical band gap energies were also obtained from absorption coefficient spectra. Our results show that as the PT content increases, the refractive index of PMN-xPT single crystals increases, while the optical band gap energy decreases. Some discussions about the BO6 octahedron building block that determines the basic energy level of PMN-xPT single crystals are also presented in this article. View full abstract»

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  • Stable violet cathodoluminescence of α-quartz after Ge+ implantation at elevated temperature

    Page(s): 1392 - 1397
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    Doping single-crystalline α-quartz with 120 keV Ge+-ion implantation under the conditions of dynamic solid phase epitaxial regrowth has been studied as function of ion fluence and substrate temperature. In particular, the light emitting properties possibly suitable for optoelectronic devices have been investigated by measuring cathodoluminescence spectra for implantation temperatures from 300 to 1223 K and for analyzing temperatures from 10-300 K. Rutherford backscattering channeling analysis showed that the Ge implantation produced amorphous layers varying in depth with temperature. At a fluence of 7×1014 Ge-ions/cm2 and an implantation temperature of 1073 K, Ge implantation is accompanied by a strong increase in the luminescence intensity of a violet band, which we associate with Ge-related defects or Ge clusters. This violet band is very stable and has a long lifetime of 6 μs. All the other bands observed are connected to known oxygen defect centers in the SiO2 network. View full abstract»

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  • Zinc oxide as an ozone sensor

    Page(s): 1398 - 1408
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    This work presents a study of intrinsic zinc oxide thin film as ozone sensor based on the ultraviolet (UV) photoreduction and subsequent ozone re oxidation of zinc oxide as a fully reversible process performed at room temperature. The films analyzed were produced by spray pyrolysis, dc and rf magnetron sputtering. The dc resistivity of the films produced by rf magnetron sputtering and constituted by nanocrystallites changes more than eight orders of magnitude when exposed to an UV dose of 4 mW/cm2. On the other hand, porous and textured zinc oxide films produced by spray pyrolysis at low substrate temperature exhibit an excellent ac impedance response where the reactance changes by more than seven orders of magnitude when exposed to the same UV dose, with a response frequency above 15 kHz, thus showing improved ozone ac sensing discrimination. View full abstract»

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  • Electrical and optical properties of CdxZn1-xTe single crystals for applications as terahertz electro-optic sensors

    Page(s): 1409 - 1412
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    CdxZn1-xTe single crystals were grown by using the Bridgman method. Hall-effect measurements showed that the carrier type and carrier concentration of unintentionally CdxZn1-xTe crystals were p type and between approximately 1014 and 1015, respectively. Phototransmission spectra showed that the position of the band edge emission shifted to higher wavelength with increasing Cd mole fraction, and photoluminescence spectra showed that the peak corresponding to the excitons bound to neutral acceptors shifted to lower energy with increasing Cd mole fraction. The electro-optic sensors fabricated utilizing the CdxZn1-xTe single crystals were operated in the terahertz spectrum range. These results can help improve the understanding of CdxZn1-xTe single crystals for applications in terahertz electro-optic sensors. View full abstract»

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  • Crystal tilting of diamond heteroepitaxially grown on vicinal Ir/SrTiO3(001)

    Page(s): 1413 - 1417
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    In the present study SrTiO3 crystals with vicinal (001) surfaces inclined and towards [110] and [100], respectively, have been used to deposit iridium layers and subsequently epitaxial diamond films. The iridium grows on top of the vicinal SrTiO3(001) with a perfect cube-on-cube registry. In contrast, the diamond films on the iridium show a strong additional tilting of up to . A model is proposed which explains the effect by the preferential incorporation of misfit dislocations due to the stress anisotropy on the vicinal substrate planes taking into account the lattice misfit and the islandlike growth mode of diamond. The experimental observations and their explanation suggest that the epitaxial diamond alignment on iridium takes place during lateral growth within the first few nanometers. View full abstract»

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  • Effects of rapid thermal annealing on the optical properties of low-loss 1.3 μm GaInNAs/GaAs saturable Bragg reflectors

    Page(s): 1418 - 1424
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    We report studies of the effect of rapid thermal annealing (RTA) on the optical properties of a low-loss 1.3 μm saturable Bragg reflector (SBR), consisting of a GaInNAs/GaAs single quantum well embedded in an AlAs/GaAs Bragg reflector grown monolithically on a GaAs substrate. RTA gives rise to a blueshift of the photoluminescence (PL) peak (and therefore of the excitonic absorption peak) and an enhancement of PL intensity, while the reflectivity properties including peak reflectivity and bandwidth are not degraded. Temperature dependent photoluminescence measurements show that the RTA-induced blueshift of photoluminescence consists of two components: one originating from the increase of optical transition energies and another from the reduction of carrier localization. Time-resolved photoluminescence results at room temperature provide information about the recombination dynamics of carriers directly relevant to the application of the SBR in laser mode locking. View full abstract»

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  • Nonlinear optical phase shift in InAs quantum dots measured by a unique two-color pump/probe ellipsometric polarization analysis

    Page(s): 1425 - 1434
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    The nonlinear optical phase shift in self-assembled InAs quantum dots (QDs) under resonant excitation in a ground-state transition was measured by a unique two-color pump/probe ellipsometric polarization analysis. This ellipsometric analysis makes use of the large optical birefringence of SK-QD [(SK) — Stranski-Krastanov] originating from the asymmetric structure. A phase shift of 0.5π rad was obtained at an input pump pulse energy density of 30 pJm2, a detuning of 11 meV, and a time delay of 20 ps in a 1 mm long waveguide having QDs with a peak wavelength of 1290 nm, a volume density of 4×1015 cm-3, and inhomogeneous broadening of 35 meV. Analysis revealed that the phase shift is mainly attributed to the absorption saturation for TE-polarized light, though other mechanisms also could contribute at higher pumping. The calculation, based on the two-level approximation, revealed that the minimum energy density for π shift is 240 fJm2, calculated under ideal conditions. View full abstract»

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  • Effect of fluorine incorporation on silicon dioxide prepared by high density plasma chemical vapor deposition with SiH4/O2/NF3 chemistry

    Page(s): 1435 - 1442
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    The effect of fluorine incorporation on properties of silicon dioxide thin films has been studied as a function of NF3/O2 gas flow ratio. Fluorine was incorporated into silicon dioxide films during high density plasma chemical vapor deposition with the SiH4/O2/NF3/He gas mixture used to improve the gap-filling ability for shallow trench isolation of devices. Refractive index measured by ellipsometry decreased with increasing NF3/O2 flow ratios for both as-deposited and annealed films. X-ray reflectivity measurements showed that both fluorine incorporation and thermal annealing reduced the film density. The analysis of infrared absorption spectra showed the relaxation of the Si-O-Si bond with increasing NF3/O2 flow ratios and thermal annealing. The secondary ion mass spectroscopy and x-ray photoelectron spectroscopy studies confirmed the behavior of fluorine diffusion and the binding energy for each species in the films, respectively. These results showed that through fluorine incorporation and thermal annealing, the network structures of silicon dioxide could be modified from low order rings to high order rings accompanied by the enlargement of nanovoids. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory