By Topic

Journal of Applied Physics

Issue 4 • Date Aug 1997

Filter Results

Displaying Results 1 - 25 of 74
  • Issue Cover

    Page(s): c1
    Save to Project icon | PDF file iconPDF (45 KB)  
    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
    Save to Project icon | PDF file iconPDF (44 KB)  
    Freely Available from IEEE
  • Are equilibrium fluctuations detectable in diffracted intensities?

    Page(s): 1507 - 1510
    Save to Project icon | PDF file iconPDF (95 KB)  

    The capability of diffraction intensity fluctuations to probe dynamic phenomena at equilibrium is studied. The summation of fluctuations over different domains that scatter incoherently, the role of statistically “white-noise” generated fluctuations and the time necessary to collect a sufficiently long signal are investigated. The factors that determine the number of incoherent regions, and maximize the relative fluctuation without reducing the count rate to such low values that impractically long acquisition times are needed are discussed. Monte Carlo simulations modeling thermally generated step fluctuations are used to illustrate the results. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Unipolar-current dipoles and other optimum reduced-symmetry multipoles

    Page(s): 1511 - 1517
    Save to Project icon | PDF file iconPDF (191 KB)  

    Two-dimensional dipole (uniform) fields produced by parallel currents are generally considered to have two symmetry planes, with a current direction reversal in reflection across one plane. Similarly, quadrupoles have four symmetry planes, and so on for higher multipoles. Expansion of the fields of filamentary currents shows that there are lower symmetry multipoles with highly uniform field characteristics. These solutions include configurations in which there is no current reversal across reflection planes, producing unipolar-current dipoles, quadrupoles, and other multipoles. In all cases, the solutions can yield systems that have the best uniformity of field characteristics (minimum undesired multipole content over the largest area) that can be achieved with the number of wires used, although the unipolar systems are less efficient and produce a lower field magnitude for a given current. These optimum solutions are not limited to circular configurations, or to systems with all wire current magnitudes identical. The configurations are easily extended by summation or integration to wire bundles or finite radius conductors. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dependence of optical gain on crystal orientation in wurtzite–GaN strained quantum-well lasers

    Page(s): 1518 - 1520
    Save to Project icon | PDF file iconPDF (348 KB)  

    Optical gains in wurtzite–GaN strained quantum-well (QW) lasers are estimated theoretically for various crystallographic directions. The calculation of the valence subbands is based on the k∙p theory, where deformation potentials are determined by a semiempirical tight-binding method. It is found that the gains in GaN strained QW lasers with non-(0001) orientations, particularly around the (101¯5) orientation, are markedly high and anisotropic, unlike those in (0001)-oriented lasers. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Characterization of refractive index change induced by electron irradiation in amorphous thin As2S3 films

    Page(s): 1521 - 1524
    Save to Project icon | PDF file iconPDF (420 KB)  

    Binary diffraction gratings in As2S3 films were prepared with the aid of an electron beam. The dose of the electrons was varied. The gratings were read with a HeNe laser, and the zero-order and first-order diffraction efficiencies were noted. Rigorous diffraction theory was used to give a homogeneous approximation for the refractive index change. Reactive ion etching was applied to reduce the thickness of the film, and a new value for the refractive index change was evaluated. The refractive index change versus film thickness dependence was found to be linear at low electron doses and Gaussian shaped at higher doses. Through a simple mathematical analysis, the absolute value of the refractive index was determined as a function of the position inside the film. At higher doses, the refractive index change was found to have a maximum value of 3%, approximately 1.2 μm from the film surface. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Measurement of laser-induced acoustic waves with a calibrated optical transducer

    Page(s): 1525 - 1531
    Save to Project icon | PDF file iconPDF (156 KB)  

    Irradiation of an absorbing material with a short laser pulse generates a thermoelastic stress wave, from which the distribution of absorbed energy can be derived. This method is ideal to measure the light penetration in biological tissue. Especially for in vivo applications, we developed an optical stress transducer that can be positioned directly in front of the irradiated surface, inside the laser beam, in order to avoid distortion of the stress wave due to acoustic diffraction. The detector is based on stress wave-induced changes of optical reflectance of a glass-water interface, probed with a continuous laser beam that is incident at an angle close to the critical angle of total internal reflection to achieve maximum sensitivity. In this study, we describe the theory for the calibration of the transducer and compare the measured with the theoretically predicted signals. In the experiments, an aqueous dye solution is irradiated with pulses from either a Q-switched, frequency-doubled Nd:yttrium aluminum garnet (YAG) laser or from an optical parametric oscillator with pulse durations of 8 and 6 ns, respectively. Good agreement between the measured and calculated waveforms as well as the possibility to obtain photoacoustic absorption spectra from the shape of the recorded signals is demonstrated. From our experimental and theoretical findings, it follows that the detector is characterized by a high temporal and spatial resolution and by an adjustable sensitivity, depending on the incident angle of the probe beam at the glass-water interface. Apart from the applications proposed in the present work, it seems to be possible to use this kind of transducer for the two-dimensional recording of stress waves. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Effects of optical penetration and laser pulse duration on laser generated longitudinal acoustic waves

    Page(s): 1532 - 1538
    Save to Project icon | PDF file iconPDF (145 KB)  

    In this article, we concentrate on the optical penetration and laser pulse duration effects on the features of the ultrasonic waves generated in a solid by a laser impact. We consider the simple case of a uniform irradiation of the sample, which we describe with the help of a simple analytical one-dimensional model. In spite of its simplicity, this model clearly highlights the competition that occurs between two temporal convolution sources, related to the optical penetration and the laser pulse duration, respectively, to produce the longitudinal arrivals on the rear side of the sample. The model is also used for an accurate description of the features of the longitudinal precursor. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Spatial and temporal characteristics of a vacuum-arc rail-gun plasma

    Page(s): 1539 - 1545
    Save to Project icon | PDF file iconPDF (126 KB)  

    The dynamics of a vacuum-arc operated rail-gun plasma were numerically simulated for the undercritically damped regime and confirmed in experiments. Analytical solutions of arc current, its velocity, and position also showed good agreement with the results. The spatial development of the arc is shown here to follow a linear behavior, even though the propulsion velocity followed an exponential-step function due to the sinusoidal nature of the arc current. Peak arc current ∼100 kA, 15 μs period was propelled to ∼106cm/s as indicated in time-of-flight measurements and simulations. The voltage signal induced on a B-dot probe by the dynamic sinusoidal arc was simulated, which compared well with the measured probe signal. A Gaussian current distribution inside the measured arc length ∼1–2 cm, was established by unfolding the B-dot probe signal. A peak magnetic field of the order 1–5 kG was also interpreted inside the arc. The emerging plasma contained ion current over tens of amperes in the pulse duration encompassing the arc envelope. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Particle accumulation in a flowing silane discharge

    Page(s): 1546 - 1553
    Save to Project icon | PDF file iconPDF (181 KB)  

    Particle trapping in different areas of a parallel-plate, radio frequency silane discharge, and its effect on plasma optical emission of SiH and Hα, has been studied under high gas-flow and low power-density conditions, as used for “device-quality” hydrogenated amorphous silicon (a-Si:H) film deposition. The largest density of particles occurs between the electrodes, near the downstream corners of the rectangular electrodes. Particles are trapped in these positions by sheath fields, until reaching sufficient size to escape with the flow. The region of strong particle trapping has an increased intensity of optical emission, with Hα increased nearly fourfold. Slow oscillatory behavior of particle scattering and discharge emission was observed for pressures near 30 Pa. Power deposited in the discharge has also been measured; for a constant rf voltage and gas-flow speed it changes weakly with pressure, with the maximum at ∼40 Pa. Combined with film growth-rate measurements, this yields a discharge energy deposition of ∼17 eV per deposited Si atom. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Use of Rietveld refinement for elastic macrostrain determination and for evaluation of plastic strain history from diffraction spectra

    Page(s): 1554 - 1562
    Save to Project icon | PDF file iconPDF (200 KB)  

    Macrostrain variations in engineering components are frequently examined using neutron diffraction, at both reactors and pulsed sources. It is desirable to minimize the sampling volume in order to maximize the spatial resolution, although this increases the required measurement time. At reactors, macrostrain behavior is inferred from a single lattice reflection (deemed to be representative of the bulk response). At a pulsed source, a complete diffraction pattern is recorded and accordingly it is natural to fit the entire diffraction spectra using a Rietveld [J. Appl. Cryst. 2, 65 (1969)] refinement. This means that an idealized crystal structure is fit to the measured distorted crystal structure, which includes deviation of the measured lattice reflections from the ideal due to elastoplastic strain anisotropies, which are dependent on the particular lattice reflection (hkl) considered. We show that elastic macrostrains calculated from lattice parameter changes in Rietveld refinements (without accounting for hkl dependent anisotropies) are almost identical to the bulk elastic response and are comparable to the response obtained from a single lattice reflection typically used by practitioners at a steady state source. Moreover good refinements on the complete pattern are obtained with short measurement times compared to what is required for good statistics for single reflections. By incorporating a description of the elastic strain anisotropy expected in cubic materials into the Rietveld code, an empirical prediction of plastic strain history is possible. The validity of these arguments is demonstrated by analysis of a uniaxial tensile load test and a reanalysis of previously reported data taken on a deformed stainless steel ring. The plastic strain predictions compare favorably with a finite element model. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • In situ transmission electron microscopy study of plastic deformation and stress-induced voiding in Al–Cu interconnects

    Page(s): 1563 - 1577
    Save to Project icon | PDF file iconPDF (6518 KB)  

    Plastic deformation in submicron wide Al-1 wt %Cu interconnects was studied in situ using a straining device in the transmission electron microscope. Dislocation motion occurred readily in unpassivated lines but was nonexistent in passivated lines due to the presence of stiff oxide sidewalls. Instead heterogeneous void nucleation occurred on straining to a critical limit. The void morphology was always near hemispherical and the nucleation always took place at the line edges. Further stretching of the lines led to a rupture of the sidewalls away from the lines, resulting in immediate dislocation motion. Void nucleation, cross slip, and operation of dislocation sources at line edges were all recorded on video. It was noted that dislocations almost parallel to the plane of the lines are rarely observed and furthermore, their movement is sluggish. Based on the dislocation configuration observed in these lines, a generalized geometrical model was arrived at in order to determine the significance of grain orientation on yield stress of passivated lines with columnar, bamboo grains. Frequent occurrence of twinning within the grains indicated that plastic deformation was indeed restricted in confined metal lines. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Modeling of thermal stresses in metal interconnects: Effects of line aspect ratio

    Page(s): 1578 - 1581
    Save to Project icon | PDF file iconPDF (83 KB)  

    Numerical results are presented on the evolution of thermal stresses in metal interconnects. Finite element analyses are carried out for a series of parallel aluminum lines embedded within silicon dioxide. The effects of line aspect ratio on the longitudinal and hydrostatic stresses in lines are investigated, for various spaces between lines. Comparisons with the results based on an isolated line under passivation are also made. It is shown that, contrary to what was frequently found by employing the single-line approach, maximum stresses in periodically arranged aluminum lines do not occur when the line width and the line height are approximately equal. The variation of stresses with line aspect ratio is affected by the spacing between lines. Implications of the present findings to the modeling of stresses and to the damage evolution through void formation are discussed. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Selection rules of Raman scattering by optical phonons in strained cubic crystals

    Page(s): 1582 - 1591
    Save to Project icon | PDF file iconPDF (234 KB)  

    Strain characterization of materials through Raman spectroscopy often requires the optical phonon wave vector to be in directions other than those of the strain-modified phonon eigenvectors. As a result, the observed mode frequencies are mixtures of the strain-modified eigenfrequencies. The selection rules for such generalized scattering configurations are derived here for the strained zincblende-diamond family crystals. The formulation is based on the relative magnitude of the LO-TO and the strain-induced splittings. The results are important for the analysis of strain-modified Raman lineshapes and of “forbidden” lines. Specific examples are worked out in detail for externally stressed bulk crystals (90° scattering geometry), and for [001], [111], and [110] strained heterojunctions (backscattering under oblique incidence and/or detection). © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Kinetics of electromigration-induced edge drift in Al–Cu thin-film interconnects

    Page(s): 1592 - 1598
    Save to Project icon | PDF file iconPDF (138 KB)  

    This article employs a one-dimensional diffusion model to study the phenomenon of electromigration-induced edge drift in a finite, Al–Cu thin-film conductor. Edge drift is caused by the accumulation of vacancies at the negative (upstream) terminal of the conductor as Al diffuses with the electrical current. When the Cu content exceeds its solubility limit, grain boundaries are decorated with Al2Cu precipitates, which must be dissolved before significant Al diffusion occurs. Assuming one-dimensional flow in a homogeneous, polygranular film, we compute the rate of growth of the precipitate-free zone at the upstream terminal, and estimate the incubation time for the onset of edge drift. The results predict an incubation time that increases with the grain size and the initial Cu content, and decreases with the square of the current density. The incubation time is inversely proportional to the “electromigration diffusivity”, DE=DBCuδZCu*, the product of the grain boundary diffusivity of Cu, the effective grain boundary thickness, and the effective valence of the Cu ion. The results are used to compare a number of prior experimental studies, which are shown (with one exception) to produce consistent values for DE. An analysis of the experimental results suggests that edge drift begins almost as soon as the precipitate-free zone length exceeds the “Blech length” for the line, suggesting that the presence of Al2Cu precipitates in the grain boundaries is essential to retard Al electromigration. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Structural evaluation of InAsP/InGaAsP strained-layer superlattices with dislocations as grown by metal-organic molecular beam epitaxy

    Page(s): 1599 - 1607
    Save to Project icon | PDF file iconPDF (2221 KB)  

    The relaxation process in InAsP/InGaAsP strained-layer superlattices (SLSs) with interfacial misfit dislocations has been investigated systematically by transmission electron microscopy (TEM) and x-ray analyses. The TEM analysis reveals that dislocations locate a little inside the buffer layer near the interface between the buffer and first well layer in the SLS. The x-ray analysis of (400) azimuthal angle dependence indicates the buffer layer has a large macroscopic tilt. Using a curve fitting analysis of various (hkl) x-ray profiles and reciprocal lattice mapping measurements, residual strain was determined quantitatively, i.e., Δa|| and Δa, in the SLS and buffer layer. These results reveal that the dislocations mainly cause lattice distortion of the buffer layer rather than relaxation of the SLS layer. The most remarkable result is that the change of a|| is not equal to that of a in the buffer layer. This phenomenon strongly suggests that microplastic domains are generated in the buffer layer. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Stability of the grain configurations of thin films—A model for agglomeration

    Page(s): 1608 - 1616
    Save to Project icon | PDF file iconPDF (199 KB)  

    We have calculated the energy of three distinct grain configurations, namely, completely connected, partially connected, and unconnected configurations, evolving during a spheroidization of polycrystalline thin film by extending a geometrical model due to Miller etal to the case of spheroidization at both the surface and film-substrate interface. “Stability” diagram defining a stable region of each grain configuration has been established in terms of the ratio of grain size to film thickness versus equilibrium wetting or dihedral angles at various interface energy conditions. The occurrence of spheroidization at the film-substrate interface significantly enlarges the stable region of unconnected grain configuration thereby greatly facilitating the occurrence of agglomeration. Complete separation of grain boundary is increasingly difficult with a reduction of equilibrium wetting angle. The condition for the occurrence of agglomeration differs depending on the equilibrium wetting or dihedral angles. The agglomeration occurs, at low equilibrium angles, via partially connected configuration containing stable holes centered at grain boundary vertices, whereas it occurs directly via completely connected configuration at large equilibrium angles except for the case having small surface and/or film-substrate interface energy. The initiation condition of agglomeration is defined by the equilibrium boundary condition between the partially connected and unconnected configurations for the former case, whereas it can, for the latter case, largely deviate from the equilibrium boundary condition between the completely connected and unconnected configurations because of the presence of a finite energy barrier to overcome to reach the unconnected grain configuration. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The synthesis, characterization, and mechanical properties of thick, ultrahard cubic boron nitride films deposited by ion-assisted sputtering

    Page(s): 1617 - 1625
    Save to Project icon | PDF file iconPDF (649 KB)  

    Significant ion irradiation is needed during growth to synthesize cubic boron nitride (cBN) films. This results in large film stresses, which have limited cBN film thicknesses to only a few hundred nm and represents a significant barrier in the development of cBN film technology. Using a new hybrid deposition technique, we have synthesized cubic BN films up to 700 nm (0.7 μm) thick. A compositional and structural analysis of the films using several standard characterization techniques confirms that relatively thick polycrystalline films with a high cBN content were synthesized. Thicker cBN films enable hardness measurements to be undertaken without major substrate effects. Nanoindentation measurements yield hardness values for the cubic BN films up to 60–70 GPa, which are greater than values measured for bulk cBN. The measured elastic modulus was observed to be lower than the bulk, and this can be accounted for by an elastic deformation of the silicon substrate. The mechanical properties of the cubic BN films are discussed with reference to other ultrahard thin films such as diamond and diamondlike carbon. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A cross-sectional atomic force microscopy study of nanocrystalline Ge precipitates in SiO2 formed from metastable Si1-xGexO2

    Page(s): 1626 - 1631
    Save to Project icon | PDF file iconPDF (416 KB)  

    In recent years, many investigators have reported visible photoluminescence from structures that consist of Ge or Si nanocrystals embedded in a SiO2 matrix deposited or grown on various substrates. We have developed a rapid technique for studying the through-thickness microstructure of this class of materials via atomic force microscopy (AFM) and, using this technique, we report on the precipitation and growth of Ge crystallites formed via a two-step process of hydrothermal oxidation of Si1-xGexO2 (x=0.15) at 450–500 °C and subsequent chemical reduction in forming gas (85/15: N2/H2; 800 °C). The Ge-particle distributions obtained with this AFM cross-sectional technique are consistent with those previously reported using other techniques. The utility of cross-sectional AFM for the evaluation of nanoscale features in the thickness of a thin film is evaluated. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Thermal oxide on CdSe

    Page(s): 1632 - 1639
    Save to Project icon | PDF file iconPDF (140 KB)  

    X-ray photoelectron spectroscopy (XPS) has been used to characterize the thin thermal oxide film grown on single crystal CdSe(0001) and polycrystalline CdSe by exposure to O2 (dry air) at 350 °C. SeOx species, where x=2,3, are clearly identified by a 5 eV shift of the Se 3d3/2,5/2 peaks to higher binding energy. A very weak shift to lower binding energy is observed for the Cd peaks. The positions of the Cd and O peaks do not match those found for the known cadmium oxides, CdO and CdO2. Instead, it is proposed that the Cd bound oxygen atoms occupy substitutional Se sites. The presence of Cd bound oxygen can also be inferred from the intensities of the SeOx, Cd, and O peaks. Raman spectroscopy confirms the existence of O in Se substitutional sites. Angle-resolved XPS is used to determine the thickness of the oxide and the relative amount of SeOx and Cd bound oxygen. The XPS data are consistent with an 8–9 Å thick oxide where 60% of the oxygen is bound to Se and 40 is bound to Cd. The data show that the oxide structure contains two layers; a passivation layer made of the SeOx species and, underneath, a layer containing oxygen in Se substitutional sites. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Charge transfer from Cu in YBa2Cu3O7-δ and Ba2Cu3O4Cl2 crystals determined by Auger electron spectroscopy

    Page(s): 1640 - 1648
    Save to Project icon | PDF file iconPDF (261 KB)  

    A formulation is proposed to estimate the charge transfer ΔqCu from Cu to some anions in metal-oxide crystals, using Auger electron spectroscopy. In the formulation, a parameter, the Auger transition probability ω, is introduced, which is defined as the ratio of Auger intensity due to a certain transition to the total Auger intensity due to other transitions when the same core electrons are primarily excited. By applying the formulation to vacuum-cleaved surfaces of YBa2Cu3O7-δ (YBCO) and Ba2Cu3O4Cl2 (BCOC) crystals, we obtained the following results: (1) YBCO cleaves between CuO2 and BaO layers, and the amount of ΔqCu is 2.3 in units of elementary electric charge. The deviation of ΔqCu from 2.0 suggests the existence of Cu3+-like atoms; (2) for BCOC, ΔqCu varies from 3.3 to 1.7 depending on the Ar ion beam sputtering time. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Monte Carlo calculation of velocity-field characteristics of wurtzite GaN

    Page(s): 1649 - 1655
    Save to Project icon | PDF file iconPDF (131 KB)  

    We present velocity-field simulations of n-doped, wurtzite-phase GaN for temperatures between 77 and 1000 K using an ensemble Monte Carlo technique. A three-valley model of the band structure is assumed, and the ionized impurity, polar optical phonon, acoustic phonon, piezoelectric, and intervally scattering mechanisms are considered. Electron degeneracy and heating are also accounted for. Properties of the two dimensional electron gas in AlGaN/GaN heterostructures are also estimated by performing simulations on bulk GaN in which the electron concentration exceeds the ionized donor concentration by factors of ten to one hundred. The simulations predict that peak steady-state drift velocities ranging from 3.3×107 to 2.1×107cm/s for temperatures between 77 and 1000 K can be achieved in both the two dimensional electron gas and in the bulk material with an ionized donor concentration of 1016cm-3. Furthermore, the simulations predict that the two-dimensional electron gas in GaN will exhibit a low-field mobility an order of magnitude greater than the bulk material, in agreement with experimental results. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Free-electron transport in semi-insulating GaAs

    Page(s): 1656 - 1660
    Save to Project icon | PDF file iconPDF (139 KB)  

    The frequency (ω) response of the admittance (Y) of Czochralski (Cz) and Bridgman (Bg) grown semi-insulating materials have been investigated in the range 300–500 K. For both materials, this conductivity remains constant up to a frequency ω at which it becomes proportional to ω1. A minimum is observed in the Y(ω) characteristics between these two regimes in Cz materials but not in Bridgman ones. It is suggested that the existence of this minimum is related to percolation induced by the presence of space-charge regions located around As precipitates and charged dislocations, which are present in Cz but not in Bg materials. The percolation invalidates the homogeneous conduction assumption made in analyzing the electrical properties of semi-insulating Cz materials. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Shift of surface Fermi level position toward the conduction band minimum by crystal defects near GaAs(001) surface

    Page(s): 1661 - 1666
    Save to Project icon | PDF file iconPDF (116 KB)  

    The effects of crystal defects near the surface on the position of surface Fermi level (EFS) are investigated using photoluminescence (PL) measurements and synchrotron radiation photoelectron spectroscopy (SRPES). For the lightly Si-doped GaAs(001) surface, PL measurements reveal that after heating to 500 °C a layer with lower PL peak intensities related to gallium vacancies than those of the bulk exists just under the thermal degraded layer. SRPES shows that EFS moves upward to 1.1–1.17 eV above the valence band maximum when this thermal degraded layer is removed by chemical etching and the excess arsenic on the surface, which is formed by rinsing the etched surface with deoxygenated and deionized water, is evaporated by heating in ultrahigh vacuum (UHV). After evaporation of excess arsenic on the surface by heating, the etching-depth dependence of EFS for a sample preheated in UHV correlated with the existence of this defect concentration layer. These results suggest that the position of EFS for the GaAs(001) surface is strongly influenced by crystal defects near the surface. © 1997 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Excitonic quantum confinement effects and exciton electroabsorption in semiconductor thin quantum boxes

    Page(s): 1667 - 1677
    Save to Project icon | PDF file iconPDF (258 KB)  

    We investigate the excitonic optical properties in thin quantum boxes in the intermediate regime between the two-dimensional (2D) and zero-dimensional (0D) with a theoretical analysis that rigorously treats excitonic confinement effects. It is found that the exciton binding energy is substantially enhanced and that the oscillator strength concentrates to the lowest excitonic transition, even in a thin box whose lateral width is considerably (about five times) larger than the Bohr radius. Novel optical properties experimentally observed in semiconductor quantum disks, which are the intense photoluminescence spectrum and ultranarrow photoluminescence excitation spectrum, are explained well by the theoretical results. We also calculate exciton absorption in a thin box in which an electric field is applied in the lateral direction. The present theory can simulate how the electroabsorption evolves from the quantum confined Stark effect in the 0D to the quantum confined Franz–Keldysh effect in the 2D with an increase in the lateral size of the box. In the intermediate regime between 2D and 0D, a strong excitonic electric-field effect, distinct from the well-known electroabsorption effects at 0D and 2D, is found. These theoretical results demonstrate that even though the lateral confinement is weak, it considerably enhances the electron–hole Coulomb interaction and alters excitonic optical features markedly in the thin quantum box. © 1997 American Institute of Physics. 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