By Topic

Journal of Applied Physics

Issue 7 • Date Oct 2010

Filter Results

Displaying Results 1 - 25 of 176
  • Two-dimensional carbon nanostructures: Fundamental properties, synthesis, characterization, and potential applications

    Page(s): 071301 - 071301-38
    Save to Project icon | PDF file iconPDF (10707 KB)  

    Since its discovery in less than five years ago, graphene has become one of the hottest frontiers in materials science and condensed matter physics, as evidenced by the exponential increase in number of publications in this field. Several reviews have already been published on this topic, focusing on single and multilayer graphene sheets. Here, we review the recent progresses in this field by extending the scope to various types of two-dimensional carbon nanostructures including graphene and free-standing carbon nanowalls/nanosheets. After a brief overview of the electronic properties of graphene, we focus on the synthesis, characterization and potential applications of these carbon nanostructures. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Preventing optical deactivation of nanocluster Si sensitized Er using nanometer-thin SiNx/SiO2:Er heterolayer thin film

    Page(s): 073101 - 073101-6
    Save to Project icon | PDF file iconPDF (790 KB)  

    Multilayer thin films consisting of nanometer-thin, Er-doped luminescent layers (either SiO2:Er or Si3N4:Er) interlaced with nanometer-thin, Si-rich sensitizing layers (either Si-rich oxide or Si-rich nitride) are proposed as a solution to loss of Er3+ optical activity during nanocluster Si (nc-Si) sensitization of Er3+. Comparison of Er3+ photoluminescence (PL) intensities and luminescence lifetimes under both direct, resonant pumping and under nc-Si sensitized pumping shows that by using a heterolayer structure that consists of Si-rich silicon nitride sensitization layers with SiO2:Er luminescing layers, anneal-induced optical deactivation and desensitization of Er3+ that often accompany nc-Si sensitization can be prevented such that the most effective nc-Si sensitization and strongest Er3+ activity can be obtained simultaneously without a compromise between the two. Based on high-resolution transmission electron microscopy and PL spectroscopy, we identify the maintenance of compositional and structural integrity of the heterolayer thin film through the use of nitride layers, and the subsequent maintenance of subnanometer scale spatial separation between nc-Si and Er3+ even after high temperature annealing at 1050 °C as being the critical factors for the observed advantage of the heterostructure. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Nonlinear optical responses of nanoparticle-polymer composites incorporating organic (hyperbranched polymer)-metallic nanoparticle complex

    Page(s): 073102 - 073102-9
    Save to Project icon | PDF file iconPDF (598 KB)  

    We report on experimental studies of the nonlinear optical properties of nanocomposites consisting of organic (hyperbranched polymer)-metallic (Au or Pt) nanoparticle complex embedded in polymer films. Open-aperture and closed-aperture z-scan techniques are used to measure the effective third-order nonlinear optical susceptibilities χeff(3) of the composites under picosecond laser radiation at a wavelength of 532 nm. The relative sign of the real and imaginary parts of χeff(3) could be explained qualitatively by the Kramers–Kronig relation. We also determined the third-order nonlinear optical susceptibilities of Au and Pt nanoparticles estimated from the measured values for χeff(3) to be (-5.48+4.76i)×10-8 esu and (4.41-0.65i)×10-6 esu, respectively, at 532 nm with a help of the Maxwell–Garnett model. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Chiral properties in a two-dimensional chiral polaritonic photonic crystal

    Page(s): 073103 - 073103-6
    Save to Project icon | PDF file iconPDF (1889 KB)  

    We theoretically investigated a format of two-dimensional dielectric-chiral photonic crystal structure that is composed of a dispersive chiral medium embedded in a dielectric background. The photonic band structure shows distinctive dispersion relationship for circularly polarized electromagnetic waves, leading to a number of intriguing wave properties, namely chirality dependent “node switching,” polarization sensitive transmission and handedness dependent mode localization. All of these effects are attributed to the strong interaction between the local resonant modes around the dispersive chiral rods and the Bloch modes of the bulk waves. The chirality dependent properties can find tremendous applications in polarization based optoelectronics devices and rapid separation of chiral compounds in pharmaceutical industry. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Radiative cooling of bulk Si by optical down-conversion

    Page(s): 073104 - 073104-4
    Save to Project icon | PDF file iconPDF (391 KB)  

    We report on the radiative cooling of an indirect band gap semiconductor through its absorption of interband incoherent light and subsequent spontaneous emission of multiple longer-wavelength photons (optical down-conversion) in conditions when the energy deficit of the process is covered by the thermal energy. The 10×10×5 mm3 Si slab kept at 473 K in an evacuated up to 10-3 torr chamber was cooled by 3.8 K when pumped with light of 1.06 μm wavelength. First-principles estimates and several advantages of the down-conversion approach over possible cooling of direct band gap semiconductors through the optical upconversion and negative luminescence are discussed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • GaN photovoltaic leakage current and correlation to grain size

    Page(s): 073105 - 073105-4
    Save to Project icon | PDF file iconPDF (970 KB)  

    GaN p-i-n solar PV structures grown by rf plasma assisted molecular beam epitaxy (MBE) produce high performance IV characteristics with a leakage current density of less than 1×10-4 mAcm-2 at 0.1 V forward bias and an on-resistance of 0.039 Ω cm2. Leakage current measurements taken for different size diodes processed on the same sample containing the solar cells reveal that current density increases with diode area, indicating that leakage is not a large function of surface leakage along the mesa. Nonannealed Pt/Au Ohmic p-contacts produce a contact resistivity of 4.91×10-4 Ω cm-2 for thin Mg doped contact layers with sheet resistivity of 62196 Ω/◻. Under concentrated sunlight the cells produce an open-circuit voltage of 2.5 V and short circuit currents as high as 30 mAcm-2. Multiple growths comprised the study and on each wafer the IV curves representing several diodes showed considerable variation in parasitic leakage current density at low voltages on some wafers and practically no variation on others. It appears that a smaller grain size within the GaN thin film accounts for higher levels of dark current. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Monte Carlo based microscopic description of electron transport in GaAs/Al0.45Ga0.55As quantum-cascade laser structure

    Page(s): 073106 - 073106-6
    Save to Project icon | PDF file iconPDF (440 KB)  

    Results of multiparticle Monte Carlo simulations of midinfrared quantum cascade lasers structure initially fabricated by Page etal are presented. The main aim of this paper is to discuss in details how electric current flows through the structure and which subbands are involved in this process. Monte Carlo method allows to predict the electron population inversion between the lasing levels and gives microscopic insight into processes leading to such behavior. Importance of a subband belonging to the laser injector region, with energy slightly below the upper lasing level, is demonstrated. The electron–electron Coulomb interactions influence the shapes of electron distribution functions; the values of average electron energies and effective subbands’ temperatures are calculated. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Three dimensional measurements of engine plumes with four-channel single spectral tomography

    Page(s): 073107 - 073107-6
    Save to Project icon | PDF file iconPDF (1713 KB)  

    The design and improvement of an aeroengine rely on the analysis of the combustion process in the combustion chamber to a certain extent. It is difficult to investigate the combustion inside the chamber directly due to its obturation and invisibility, however, the physical distribution of exhaust plumes outside the chamber can be measured by various means and provide the information to deduce the combustion condition inside the chamber. Most traditional measurementations such as thermography can only measure the plane temperature distribution of the plumes, hence its applications are restrained. In this paper, a three dimensional (3D) measurement approach is proposed, which is based on a multichannel single spectral tomography (SST) and the radiation theory of blackbody. Furthermore, an SST real-time testing system was built to measure the 3D temperature distribution of the plumes of a pulse detonation engine. To improve the precision of the testing system, an emission projection matrix was proposed and the relationship between the radiant intensity of blackbody and the gray scale of the photoelectronic sensor was also deduced. Theoretical analysis and experimental results prove the feasibility of the proposed SST approach that can be promoted to apply to the 3D measurement of plumes of other aeroengines. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Area-transformation method for designing invisible cloaks

    Page(s): 073108 - 073108-4
    Save to Project icon | PDF file iconPDF (1894 KB)  

    By means of area-transformation method, the material parameters of the invisible cloaks in elliptic-cylindrical and spherical coordinates were obtained. The material parameters of the invisible cloaks are nonsingular and the cloaks can operate in a wide bandwidth due to the area-transformation rather than the point-transformation. The invisible properties of the cloaks are nearly perfect when the original area is small enough compared with its counterpart in the transformed space. Full wave simulations based on finite element method verified the designed cloaks. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Influence of Ag thickness on structural, optical, and electrical properties of ZnS/Ag/ZnS multilayers prepared by ion beam assisted deposition

    Page(s): 073109 - 073109-5
    Save to Project icon | PDF file iconPDF (534 KB)  

    The structural, optical, and electrical characteristics of zinc sulfide (ZnS)/Ag/ZnS (ZAZ) multilayer films prepared by ion beam assisted deposition on k9 glass have been investigated as a function of Ag layer thickness. The characteristics of ZAZ multilayer are significantly improved up insertion of optimal Ag thickness between ZnS layers. The results show that due to bombardment of Ar ion beam, distinct Ag islands evolve into continuous Ag films at a thin Ag thickness of about 4 nm. The thinner Ag film as a thickness of 2 nm leads to high sheet resistance and low transmittance for the interface scattering induced by the Ag islands or noncontinuous films; and when the Ag thickness is over 4 nm, the ZAZ multilayer exhibits a remarkably reduced sheet resistance between 7–80 Ω/sq for the increase in carrier concentration and mobility of Ag layer, and a high transmittance over 90% for the interference phenomena of multilayers and low absorption and surface scattering of Ag layer. The ZAZ multilayer with 14 nm Ag film has a figure of merit up to 6.32×10-2 Ω-1, an average transmittance over 92% and a sheet resistance of 7.1 Ω/sq. The results suggest that ZAZ film has better optoelectrical properties than conditional indium tin oxide single layer. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optical forces on arbitrary shaped particles in optical tweezers

    Page(s): 073110 - 073110-8
    Save to Project icon | PDF file iconPDF (1045 KB)  

    Discrete dipole approximation (DDA) method is an efficient method for computing electromagnetic (EM) field of nanometer/micrometer-sized dielectric particles with arbitrary geometric shape and topology. In this work we employ the DDA method to calculate the optical force of dielectric shaped particles embedded in optical tweezers made from focused Gaussian laser beams. The EM force is calculated based on the self-consistent solution of EM field distribution and discrete dipole moment distribution within the particles. The DDA method agrees well with the Mie theory for spherical dielectric particles and this supports the effectiveness of the DDA method in handling optical forces in optical tweezers. The optical force for shaped particles such as cubes, rectangles, cylinders, and core-shell composite particles shows many interesting features. The force strongly depends on the orientation of the particle with respect to the laser beam propagation and polarization direction and the aspect ratio of the anisotropic particle. For a core-shell composite particle the zero-force balance point shifts from the particle center to its two sides. When an additional particle comes close a trapped particle, the perturbation effect strongly depends on the relative location of the center of the focused laser beam with respect to the two particles. Furthermore, the geometry of shaped particles not only affects the magnitude of the optical force but also influences the optical trap stiffness. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Microphotoluminescence investigation of InAs quantum dot active region in 1.3 μm vertical cavity surface emitting laser structure

    Page(s): 073111 - 073111-5
    Save to Project icon | PDF file iconPDF (434 KB)  

    Microphotoluminescence -PL) investigation has been performed at room temperature on InAs quantum dot (QD) vertical cavity surface emitting laser (VCSEL) structure in order to characterize the QD epitaxial structure which was designed for 1.3 μm wave band emission. Actual and precise QD emission spectra including distinct ground state (GS) and excited state (ES) transition peaks are obtained by an edge-excitation and edge-emission (EEEE) μ-PL configuration. Conventional photoluminescence methods for QD-VCSELs structure analysis are compared and discussed, which indicate the EEEE μ-PL is a useful tool to determine the optical features of the QD active region in an as-grown VCSEL structure. Some experimental results have been compared with simulation results obtained with the aid of the plane-wave admittance method. After adjustment of epitaxial growth according to EEEE μ-PL measurement results, QD-VCSEL structure wafer with QD GS transition wavelength of 1300 nm and lasing wavelength of 1301 nm was obtained. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance study of high operating temperature HgCdTe mid wave infrared detector through numerical modeling

    Page(s): 073112 - 073112-10
    Save to Project icon | PDF file iconPDF (879 KB)  

    The design of present generation uncooled Hg1-xCdxTe infrared photon detectors relies on complex heterostructures with a basic unit cell of type n_+/π/p_+. We present an analysis of double barrier n_+/π/p_+ mid wave infrared (x=0.3) HgCdTe detector for near room temperature operation using numerical computations. The present work proposes an accurate and generalized methodology in terms of the device design, material properties, and operation temperature to study the effects of position dependence of carrier concentration, electrostatic potential, and generation-recombination (g-r) rates on detector performance. Position dependent profiles of electrostatic potential, carrier concentration, and g-r rates were simulated numerically. Performance of detector was studied as function of doping concentration of absorber and contact layers, width of both layers and minority carrier lifetime. Responsivity ∼0.38 AW-1, noise current ∼6×10-14 A/Hz1/2 and D* ∼3.1×1010cmHz1/2W-1 at 0.1 V reverse bias have been calculated using optimized values of doping concentration, absorber width and carrier lifetime. The suitability of the method has been illustrated by demonstrating the feasibility of achieving the optimum device performance by carefully selecting the device design and other parameters. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Photonic crystals with defect structures fabricated through a combination of holographic lithography and two-photon lithography

    Page(s): 073113 - 073113-4
    Save to Project icon | PDF file iconPDF (1268 KB)  

    This paper presents the capability of direct laser writing of complex defect structures in holographically formed three-dimensional photonic crystals in dipentaerythritol penta/hexaacrylate (DPHPA) monomers mixed with photoinitiators. The three-dimensional photonic crystal template was fabricated through prism-based holographic lithography. Defect structures are fabricated through the two-photon polymerization excited by a femtosecond laser. The strengths of two optical lithographic techniques are combined with holographic lithography providing a rapid and large area microfabrication and two-photon lithography providing flexibility in fabrication of defect structures. The optical fabrication process is simplified in the negative tone DPHPA without prebake and postexposure bake as is required of SU-8 while maintaining a capability for constructing photonic structures with small features. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Self-organized, gratinglike nanostructures in polymer films with embedded metal nanoparticles induced by femtosecond laser irradiation

    Page(s): 073114 - 073114-10
    Save to Project icon | PDF file iconPDF (1996 KB)  

    The self-organized formation of periodic superstructures in thin plasma polymer films containing noble metal nanoparticles upon femtosecond laser irradiation has been studied in detail. By applying several hundred laser pulses on average per spot, the nanostructure of the metal layer is persistently changed into an approximate line grating with periodical changes in particle size and shape as observed by scanning and transmission electron microscopy. The formation of the structures is only possible within rather narrow ranges of laser intensity and metal content. The orientation of the lines is given by the laser polarization, while their spatial periodicity depends on laser wavelength and incidence angle. These observations give evidence that interference of incident light with light scattered into the film plane is the main mechanism controlling the nanostructure formation. We also discuss the optical spectra of the irradiated regions, in particular the observed dichroism and its relation to the prepared periodic structures. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Blue-green and white color tuning of monolithic light emitting diodes

    Page(s): 073115 - 073115-6
    Save to Project icon | PDF file iconPDF (318 KB)  

    A blue light emitting diode (LED) is grown on top of a (Ga, In)N/GaN multiple quantum well (QW) acting as a light converter from blue to green-yellow wavelength. The blue light is produced by electrical injection, while the green-yellow emitting QWs are optically pumped by the blue photons. It is shown that the final color of the LED is strongly dependent on the blue pumping wavelength, the absorption and the internal quantum efficiency of the light converter. Depending on these parameters, blue to green LEDs or even white LEDs can be obtained. In addition, the injection current dependence of the LED electroluminescence is measured and analyzed. A very low blueshift is observed as a function of the injection current. It is explained by the fact that the carrier density per QW in the light converter stays relatively low compared to the case of classical current-injected green LEDs. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A simultaneous multiple-section photoacoustic imaging technique based on acoustic lens

    Page(s): 073116 - 073116-7
    Save to Project icon | PDF file iconPDF (609 KB)  

    In this paper, we propose a simultaneous multiple-slice photoacoustic (PA) imaging technique by utilizing an acoustic lens with parallel imaging ability. Our method can directly image multiple slices of the three-dimensional (3D) PA images in real-time without utilizing special reconstruction algorithms. Combining the advantages of an acoustic lens with long focal depth and a fast data acquisition system with high sampling rate, the new system can acquire all slices of a 3D object simultaneously. This is achieved by utilizing the time-resolved technique that allows to distinguish PA signals from different object planes. According to the experiment results, the reconstructed sectional images match the original samples well. The proposed technique provides a fast and reliable approach to multiple-section PA imaging. Our study can be applied to noninvasive imaging and medical diagnosis. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Laser peen forming induced two way bending of thin sheet metals and its mechanisms

    Page(s): 073117 - 073117-7
    Save to Project icon | PDF file iconPDF (1026 KB)  

    Laser peen forming, is a purely mechanical forming method achieved through the use of laser energy to form complex shapes or modify curvatures. It is flexible and independent of tool inaccuracies that result from wear and deflection. Its nonthermal process makes it possible to form sheet metal without material degradation or even improve them by inducing compressive stress over the target surface. Experimental investigation has been carried out to understand the effect of process parameters such as laser intensity, scanning velocity on the bending deformation of thin sheet metal with different thicknesses. It is found that the sheet metal can be made to bend not only toward but also away from the laser beam depending on the process condition. The bending deformation is found to be varied continuously and smoothly from the concave form to the convex by increasing the sheet thickness or decreasing the laser intensity. There is also a specific thickness for sheet metal to remain flat after laser peen forming. Two mechanisms are proposed to understand all experimental results, which are shock bending mechanism and stress gradient mechanism for bending toward and away from the laser beam, respectively. Due to the coupling effect of two mechanisms, the smoothly switching from one mechanism to the other depending on process conditions makes the laser peen forming to be an easily controlled process for forming complex shapes and high precision curvature modification. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Scalar theory of electromagnetic wave in a spherically symmetric radially anisotropic and inhomogeneous medium: Photonic atoms

    Page(s): 073118 - 073118-6
    Save to Project icon | PDF file iconPDF (278 KB)  

    Based on quantum mechanical angular momentum operators, we establish a scalar potential theory for describing electromagnetic wave in a spherically symmetric radially anisotropic and inhomogeneous dielectric medium. The developed scalar theory is validated by rederiving the prescription for spherical invisible cloaking against electromagnetic wave. As an application of the scalar potential theory, it is shown that under appropriate radial anisotropy conditions photons can be localized, in a manner that is analogous to the bounded electrons in atoms. We refer to such localized states as the photonic atoms in order to reflect their conceptual significance as an extension to the analogies between photons and electrons. The developed scalar potential theory is expected to be helpful in practice. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Mechanisms of high quality i-ZnO thin films deposition at low temperature by vapor cooling condensation technique

    Page(s): 073119 - 073119-6
    Save to Project icon | PDF file iconPDF (1020 KB)  

    A comparative mechanism investigation on the structural and optoelectronic properties of i-ZnO thin films, deposited on the silicon substrates at various temperatures were conducted. The experimental results verified that the i-ZnO films deposited at a low temperature have better quality over the conventional high temperature deposited ones. This low temperature deposition by using vapor cooling condensation technique has been successfully used to fabricate optoelectronic devices, such as UV light-emitting diodes and UV photodetectors. The mechanisms responsible for the fact that the low temperature deposited samples had better quality were analyzed in terms of the adsorption/desorption and diffusion of ZnO particles in the growth process. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Self-consistent electrodynamics of large-area high-frequency capacitive plasma discharge

    Page(s): 073301 - 073301-10
    Save to Project icon | PDF file iconPDF (4697 KB)  

    Capacitively coupled plasmas (CCPs) generated using high frequency (3–30 MHz) and very high frequency (30–300 MHz) radio-frequency (rf) sources are used for many plasma processing applications including thin film etching and deposition. When chamber dimensions become commensurate with the effective rf wavelength in the plasma, electromagnetic wave effects impose a significant influence on plasma behavior. Because the effective rf wavelength in plasma depends upon both rf and plasma process conditions (e.g., rf power and gas pressure), a self-consistent model including both the rf power delivery system and the plasma discharge is highly desirable to capture a more complete physical picture of the plasma behavior. A three-dimensional model for self-consistently studying both electrodynamic and plasma dynamic behavior of large-area (Gen 10, >8 m2) CCP is described in this paper. This model includes Maxwell’s equations and transport equations for charged and neutral species, which are coupled and solved in the time domain. The complete rf plasma discharge chamber including the rf power delivery subsystem, rf feed, electrodes, and the plasma domain is modeled as an integrated system. Based on this full-wave solution model, important limitations for processing uniformity imposed by electromagnetic wave propagation effects in a large-area CCP (3.05×2.85 m2 electrode size) are studied. The behavior of H2 plasmas in such a reactor is examined from 13.56 to 200 MHz. It is shown that various rectangular harmonics of electromagnetic fields can be excited in a large-area rectangular reactor as the rf or power is increased. The rectangular harmonics can create not only center-high plasma distribution but also high plasma density at the corners and along the edges of the reactor. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A general model for chemical erosion of carbon materials due to low-energy H+ impact

    Page(s): 073302 - 073302-7
    Save to Project icon | PDF file iconPDF (502 KB)  

    Modeling the chemical erosion of carbon materials due to low-energy H+ impact is of paramount importance for the prediction of the behavior of carbon-based plasma-facing components in nuclear fusion devices. In this paper a simple general model describing both energy and temperature dependence of carbon-based chemical erosion is presented. Enlightened by Hopf’s model {Hopf etal, [J. Appl. Phys. 94, 2373 (2003)}, the chemical erosion is separated into the contributions from three mechanisms: thermal chemical erosion, energetic chemical sputtering, and ion-enhanced chemical erosion. Using input from the Monte Carlo code TRIDYN, this model is able to reproduce experimental data well. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The mechanism of low-k SiOCH film modification by oxygen atoms

    Page(s): 073303 - 073303-10
    Save to Project icon | PDF file iconPDF (853 KB)  

    The interaction of oxygen atoms with three types of plasma enhanced chemical vapor deposition low-k SiOCH films is studied. The samples were treated by O atoms in the far plasma afterglow conditions in a special experimental system designed for this study. The experimental system allowed avoiding the effect of ions and vacuum ultraviolet (VUV) photons on surface reactions and controlling the oxygen atom concentration over the samples. Fourier-transform infrared spectroscopy, x-ray fluorescence, and atomic force microscopy techniques were used to analyze the changes occurring in low-k films. Monte Carlo model for O atom interaction with low-k material that includes penetration, recombination, and reactions with methyl groups was developed. It is shown that the surface recombination on the pore wall surface determines the profile and penetration depth of O atoms into the films. The reaction of O atoms with methyl groups has lower probability and therefore proceeds in the background mode. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Impact of temperature increments on tunneling barrier height and effective electron mass for plasma nitrided thin SiO2 layer on a large wafer area

    Page(s): 073304 - 073304-9
    Save to Project icon | PDF file iconPDF (449 KB)  

    Thermally grown SiO2 layers were treated by a plasma nitridation process realized in a vertical furnace. The combination of a pulsed-low frequency plasma and a microwave remote plasma with N2/NH3/He feed gas mixture was used to nitride the thermally grown SiO2 gate dielectrics of MIS structures. Temperature dependency of effective masses and the barrier heights for electrons in pure thermally grown SiO2 as well as plasma nitrided SiO2 in high electric field by means of Fowler–Nordheim regime was determined. It is frequently seen from the literature that either effective electron mass or barrier height (generally effective electron mass) is assumed to be a constant and, as a result, the second parameter is calculated under the chosen assumption. However, in contrast to general attitude of previous studies, this work does not make any such assumptions for the calculation of neither of these two important parameters of an oxide at temperature ranges from 23 to 110 °C for SiO2, and 23 to 130 °C for nitrided oxide. It is also shown here that both parameters are affected from the temperature changes; respectively, the barrier height decreases while the effective mass increases as a result of elevated temperature in both pure SiO2 and plasma nitrided SiO2. Therefore, one parameter could be miscalculated if the other parameter, i.e., effective mass of electron, was assumed to be a constant with respect to variable physical conditions like changing temperature. Additionally, the - - barrier heights were calculated just by taking constant effective masses for both types of oxides to be able to compare our results to common literature values. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Spectroscopic analysis of Eu3+ -and Eu3+:Yb3+-doped yttrium silicate crystalline powders prepared by combustion synthesis

    Page(s): 073501 - 073501-6
    Save to Project icon | PDF file iconPDF (1131 KB)  

    Yttrium silicate powders doped with Eu3+ and codoped with Eu3+ and Yb3+ were prepared by combustion synthesis. The x-ray powder diffraction data showed the presence of Y2SiO5 and Y2Si2O7 crystalline phases. Singly doped (1 wt%) sample illuminated with ultraviolet light (λ=256 nm) showed the characteristic red luminescence corresponding to 5D07FJ transitions of Eu3+. The Judd–Ofelt intensity parameters were calculated from experimental data and the radiative and nonradiative relaxation rates were estimated. The results showed that the nonradiative relaxation rate is smaller in yttrium silicate compared to yttrium oxide powder, a reference material, prepared under similar conditions. Codoped samples were exposed to near-infrared laser excitation (λ=975 nm) and the red luminescence of Eu3+ was also observed. In this case, the luminescence is achieved due to a cooperative upconversion (CUC) process involving energy transfer (ET) from pairs of ytterbium ions to europium ions. The ET rate was estimated by fitting a rate equation model with the dynamics of CUC red emission. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

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

Full Aims & Scope

Meet Our Editors

Editor
P. James Viccaro
Argonne National Laboratory