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Journal of Applied Physics

Issue 4 • Date Feb 2006

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Displaying Results 1 - 25 of 77
  • Issue Cover

    Page(s): c1
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  • Issue Table of Contents

    Page(s): toc1
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  • Impact of band gap shrinkage on simulated bifurcation routes in directly modulated semiconductor lasers

    Page(s): 043101 - 043101-7
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    A carrier heating model is derived by taking into account the various temperature processes in the active layer of laser diodes. This model is then used to simulate the static and dynamic characteristics of a directly modulated 1.55 μm distributed-feedback laser diode. The calculated results are compared with the measured results of this device as obtained in an earlier work [H. F. Liu and W. F. Ngal, IEEE J. Quantum Electron. 29, 1668 (1993)], and this reveals the significant impact of band gap shrinkage on simulated results. This study also shows that the carrier heating model is a self-consistent model that naturally describes the gain suppression phenomena in directly modulated laser diodes. View full abstract»

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  • Modeling of isotropic backward-wave materials composed of resonant spheres

    Page(s): 043102 - 043102-7
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    A possible realization of isotropic artificial backward-wave materials is theoretically analyzed. An improved mixing rule for the effective permittivity of a composite material consisting of two sets of resonant dielectric spheres in a homogeneous background is presented. The equations are validated using the Mie theory and numerical simulations. The effect of a statistical distribution of sphere sizes on the increase of losses in the operating frequency band is discussed and some examples are shown. View full abstract»

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  • Transient electron excitation in laser-induced plasma-assisted ablation of transparent materials

    Page(s): 043301 - 043301-6
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    We investigate the mechanism of laser-induced plasma-assisted ablation (LIPAA), by which high-quality and high-efficiency ablation of transparent materials, such as glass, can be performed with a single conventional pulsed laser. The laser-induced plasma induces transient absorption of the laser beam (532 nm) by the glass substrate. The origin of the transient absorption is electron excitation by ions with kinetic energy more than approximately 10 eV in the plasma, which is observed by measuring transient polarization change in the glass substrate applied with a high external pulsed electric field during the plasma-assisted electron excitation (plasma-conductivity measurement). A possible mechanism of LIPAA is proposed based on the results obtained. View full abstract»

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  • Spatial variation of plasma parameters and ion acceleration in an inductive plasma system

    Page(s): 043302 - 043302-5
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    Plasma parameters of inductively coupled plasma system with an annular plasma source have been studied experimentally. At low pressures (about 1 mTorr), electron temperature inside the plasma source is rather high (8–13 eV) and is much greater than in the diffusion (main) chamber (4–5 eV). The plasma potential inside the source is also much higher than in the main chamber. There is a rapid drop of the electron temperature and plasma potential at the boundary between the plasma source and the main chamber. The drop of the plasma potential at the boundary (about 20 V) means the existence of a strong axial electric field, which retards the electrons inside the plasma source and accelerates the ions from the source into the main chamber. Measurements of ion energy distributions in the main chamber volume reveal the existence of ions with kinetic energies about 15 eV. View full abstract»

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  • Modeling and experimental investigation of spot dynamics on graphite cathodes in dc plasma arcs at high pressure

    Page(s): 043303 - 043303-6
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    From a model recently developed for refractory cathodes [Muñoz-Serrano etal, J. Appl. Phys.98, 093303 (2005)], the behavior of a graphite cathode spot in a dc plasma torch at atmospheric pressure was investigated. Furthermore, an experimental study of these cathodes was made guided by the results obtained from the model. The model includes the modeling of the cathode region, the solution of the heat conduction problem in the cathode, and the simulation of the cathode ablation process. As a result of the model, the values of the parameters which characterize the cathode region were obtained, and the evolution of the spot under different working conditions determined by the value of the initial voltage drop in the cathode region, U0, was investigated. The results obtained show that the maximum spot radius diminishes when U0 increases. Furthermore, two qualitatively different conditions for the spot dynamics were found. For U0≥31 V, the spot radius continually grows over time until reaching a maximum value rm, and the spot remains fixed on a point of the cathode surface. For values of U0 less than 31 V the spot radius continues growing over time until reaching a maximum value with which it is not possible to satisfy the energy balance equation. This leads to spot extinction and to its appearance at another point of the cathode surface. Several graphite cathodes were experimentally studied, each one using different interelectrode voltage drop values Ua-c. Before and after arcing, the cathode surface was explored by an electron microscope, and the roughness profile of that surface was determined by a perthometer. This allowed measuring the average size of the craters produced on the cathode surface by the arc. The mo- vement of the spot attachment for different values of interelectrode voltage was observed by a digital video camera. It was experimentally found that the average crater radius diminished when the Ua-c potential increased. Furthermore, it was seen that for Ua-c values less than 32 V, the spot moved over the cathode surface and that this movement became slower when the Ua-c increased. The spot became immobile for Ua-c=32 V. These experimental results corroborate the spot behavior obtained from the theoretical model. View full abstract»

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  • Hydrodynamic model for a vacuum arc operated with background gas: Theory and experimental validation

    Page(s): 043304 - 043304-7
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    A stationary, one-dimensional fluid model is presented to describe the interelectrode region of a nonfiltered vacuum arc operated with a background gas. The model includes the electron energy equation and the main elastic and inelastic atomic processes among metallic ions, electrons, and gas particles. To validate the model predictions an experimental study of the plasma-neutral gas structure, using a titanium (Ti) cathode and argon (Ar) as the background gas, is presented. The measured electron temperature and the experimental dependence on the pressure of neutral Ti and Ar spectroscopic emission lines are well reproduced, using a simple atomic model to interpret the plasma radiation emission. View full abstract»

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  • Probing the intermixing in In(Ga)As/GaAs self-assembled quantum dots by Raman scattering

    Page(s): 043501 - 043501-8
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    We show that Raman scattering is a sensitive technique for probing the degree of Ga intermixing in In(Ga)As/GaAs self-assembled quantum dots (QDs). The shifts of the QD phonon frequency that we observe are explained by the modification of the strain due to Ga incorporation into the QDs from the GaAs matrix during growth. Using an elastic continuum model, we estimate the average In content of the dots from the QD phonon frequency. The varying amount of intermixing in QDs grown with different In compositions, QD layer thicknesses, growth temperatures, and stacking spacer layer thicknesses are investigated. The Raman data indicate that Ga intermixing is larger for QD samples with low In(Ga)As coverage thickness and/or high growth temperature and, in multilayered systems, for samples with small GaAs spacer layers. View full abstract»

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  • Sulfur incorporation into copper indium diselenide single crystals through annealing in hydrogen sulfide

    Page(s): 043502 - 043502-5
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    CuInSe2 crystals were sulfurized in a H2SAr gas mixture at 575 °C. The focus was on the resulting mass transport, in particular, on the interdiffusion of Se and S. Experiments were done for various sulfurization times, and the resulting S distribution was measured by Auger electron spectroscopy sputter depth profiling and analyzed with the Boltzmann-Matano method. A one-dimensional diffusion process had shaped the S distribution in these crystals. The respective diffusion coefficient was on the order of 10-16 cm2/s, and it varied only slightly with the S content in CuIn(Se,S)2. View full abstract»

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  • Nonequilibrium radiation of long-wavelength InAs/GaSb superlattice photodiodes

    Page(s): 043503 - 043503-7
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    The emission behavior of binary-binary type-II InAs/GaSb superlattice photodiodes has been studied in the spectral range between 8 and 13 μm. With a radiometric calibration of the experimental setup the internal and external quantum efficiencies have been determined in the temperature range between 80 and 300 K for both the negative and positive luminescences. The negative luminescence efficiency approaches values as high as 35% without antireflection coating. An analytic description of the temperature dependence of the internal quantum efficiency around a zero-bias voltage allows for the determination of the coefficient for electron-hole-electron Auger recombination Γn=1×1024 cm6 s-1. For an n-type material, the minority-carrier lifetime is provided as a function of band gap and temperature, explaining the strong decrease of the minority-carrier lifetime in the case of an n-type residual background exceeding 1×1016 cm-3. Furthermore, an analytic expression of the quantum efficiency for the radiation upon forward-bias conditions is given. View full abstract»

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  • Film/substrate interface stability in thin films

    Page(s): 043504 - 043504-6
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    We examined the morphological stability of an interface between a misfitting thin film and a substrate within the framework of linear stability theory. An interface instability exists regardless of the mismatch between the elastic properties of the film and the substrate and the magnitude of the interface energy. Stiffer substrates, smaller misfits, and larger interface energies all tend to reduce the range of wave numbers (to smaller values) over which the instability exists. We demonstrate that the film itself is unstable in all circumstances, even under conditions where the free surface remains flat. In other words, a misfitting film on a substrate is always unstable. We also demonstrate that the interface instability is enhanced when the interface can slip than when it cannot. View full abstract»

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  • Atomic scale structure and morphology of (In,Ga)As-capped InAs quantum dots

    Page(s): 043505 - 043505-6
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    The atomic scale morphology of InAs/GaAs quantum dots (QDs) capped with In0.1Ga0.9As layers of different thickness are studied using in situ scanning tunneling microscopy (STM) and compared to the effects of capping with a pure GaAs layer. QDs capped with a 5 nm In0.1Ga0.9As layer exhibit a longer photoluminescence emission wavelength than those capped with GaAs. STM studies show that the QDs capped with In0.1Ga0.9As retain their height during the initial stages of capping (up to ∼2 nm), whereas the GaAs-capped QDs collapse as material migrates from their tops onto the cap surface. After deposition of a 25 nm GaAs cap the surface is still far from flat, whereas the In0.1Ga0.9As capping layer is planar after just 5 nm deposition. High-resolution STM images, supported by reflection high-energy electron diffraction measurements, reveal a (4×3)/c(4×6) reconstruction for the In0.1Ga0.9As cap, whereas the GaAs cap layer rapidly exhibits a c(4×4) reconstruction after the first few monolayers of deposition. The planar morphology is a consequence of enhanced In adatom diffusion on the InGaAs alloy surface. View full abstract»

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  • Multilevel based analysis of the thermoluminescence of CaSO4:RE (RE=Tm, Dy, Tb, and Sm)

    Page(s): 043506 - 043506-8
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    Multitrapping levels feature of thermoluminescent (TL) phosphors of CaSO4:RE (RE=Dy, Tb, and Sm) were analyzed using a variable heating rate method (including extremely slow heating rates of 0.001 °C s-1), the postannealing method, and the analysis of TL decay curves using x-ray induced luminescence (XIL) spectroscopy after x-ray excitation was cut off at temperatures between 100 and 240 °C. All the data confirmed the multilevel feature of the TL levels. The ranges of activation energies E of these components in the main glow were determined to be (a) 1.64-2.03 eV for CaSO4:Dy, (b) 1.66-2.01 eV for CaSO4:Tb, and (c) 1.66-2.00 eV for CaSO4:Sm. The frequency factor s was determined to be 1019 s-1 for all components of the phosphors. The previously reported TL properties of the CaSO4:Tm phosphor were reinvestigated using the XIL decay analysis. Assuming that the most populated level is located at the center of the main glow, the four phosphors have similar E values of ∼1.8 eV. The present results imply that the multicomponent TL properties of rare-earth-doped CaSO4 phosphors are characterized by a lattice of CaSO4 involving defects introduced around RE3+ ions, and the glow curve properties are essentially not dependent on the rare-e- arth species introduced. View full abstract»

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  • Raman scattering from epitaxial HfN layers grown on MgO(001)

    Page(s): 043507 - 043507-4
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    Stoichiometric single-crystal HfN layers grown on MgO(001) are analyzed by Raman spectroscopy. Second-order Raman scattering predominates, but first-order modes in the acoustic and optical ranges are also visible. The latter indicates that the Oh symmetry of NaCl-structure HfN is broken. The large mass difference between Hf and N leads to a correspondingly large separation, 250 cm-1, between the first-order acoustic and optical bands. Within this gap, four Raman lines are clearly observed. The first three are the second-order transverse acoustic mode (240 cm-1), the sum of the first-order transverse and longitudinal acoustic modes (280 cm-1), and the second-order longitudinal acoustic mode (325 cm-1). The fourth line at 380 cm-1 is identified as the difference between the first-order optical and acoustic modes. The observed first-order Raman scattering, as well as the width of the gap between the first-order acoustic and optical modes, is in good agreement with previously calculated HfN phonon density of states. View full abstract»

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  • Defect centers and optical absorption edge of degenerated semiconductor ZnO thin films grown by a reactive plasma deposition by means of piezoelectric photothermal spectroscopy

    Page(s): 043508 - 043508-7
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    Undoped and Ga-doped (3 wt %) n-type ZnO thin films were grown by a reactive plasma deposition method on glass substrates at 200 °C under an oxygen flow rate from 0 to 50 SCCM. In this paper, we report on the defect and band edge related signals in the optical absorption spectra for ZnO thin film by using a piezoelectric photothermal (PPT) spectroscopy, which is effective in observing a nonradiative transition process. The PPT peak around 2.5 eV was observed only for the undoped ZnO samples grown under a low oxygen flow rate. This signal is considered to be related to the oxygen vacancies, because it disappears with the increase of the oxygen flow rates. No corresponding peak was found for the Ga-doped samples. This result indicates that Ga doping inhibits the generation of the oxygen vacancies, and it agrees with that from the first-principle electronic band structure calculations. We have also carried out the theoretical calculation for the optical absorption edge of degenerated ZnO as a function of the carrier concentration. Burstein-Moss effect and band-gap-narrowing effect in ZnO should be considered in the case of high carrier concentration. Comparing the experimental results with the theoretical predictions, we found out that the proposed PPT edge energy coincides well with the Fermi level EF. View full abstract»

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  • Influence of metal trapping on the shape of cavities induced by high energy He+ implantation

    Page(s): 043509 - 043509-5
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    In He implantation induced cavities highly contaminated with metals (Au, Ni, Pt) we found that, when no three-dimensional structure is observed, the shape of the cavities can be strongly modified depending on the nature of the metal and on its trapped quantity. The equilibrium shape of cavities is the Wulff shape associated with the minimum surface energy which can be determined using the code WULFFMAN. On the basis of these computations the effect of a metal chemisorption may be accounted for. At very low coverage (far below 1%) there is no effect to be expected. At coverages between 1% and 10%, independent of the nature of the metal, a reduction of the specific surface energy of the vicinal surfaces may produce spherical cavities. Eventually for coverages close to one monolayer, the specific surface energy of the concerned metal will drive the cavities toward spherical or highly facetted shapes depending on whether the specific energy of the metal is smaller or higher than the vicinal one of silicon. View full abstract»

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  • Rotational and vibrational state distributions of H2 activated on a heated tungsten filament

    Page(s): 043510 - 043510-6
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    The rotational and vibrational state distributions of H2 activated on a heated tungsten filament were determined by employing a coherent anti-Stokes Raman scattering technique to examine the contribution to the catalytic chemical vapor deposition process. The rotational excitation could be confirmed and the distribution was Boltzmann-like. When the filament temperature was 2700 K and the H2 pressure was over 1.3 kPa, the rotational temperature monitored 5 cm under the filament was around 1200 K; it showed a sharp decrease below 670 Pa and it was 700 K at 67 Pa. This decrease in the rotational temperature suggests the importance of relaxation processes on the chamber walls. The first vibrationally excited H2 molecules could also be identified at pressures over 670 Pa and the vibrational temperature was not much different from the rotational one. This vibrational temperature is much lower than those in typical H2 plasma, showing that the direct vibrational excitation of H2 on hot filaments is inefficient compared to its dissociation to two H atoms. View full abstract»

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  • Near edge x-ray absorption fine structure study of aligned π-bonded carbon structures in nitrogenated ta-C films

    Page(s): 043511 - 043511-5
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    Polarization dependent studies of near edge x-ray absorption fine structure (NEXAFS) show evidence for the presence of aligned π-bonded carbon structures and the formation of a nonplanar CN phase in tetrahedral amorphous nitrogenated carbon (ta-CN) films deposited at room temperature. Moreover, the analysis of NEXAFS data as a function of nitrogen concentration and annealing temperature leads to a comprehensive assignment of the local CN bonding configurations in these ta-CN films and suggests an unusual and almost thermally stable nitrogenated carbon structure. View full abstract»

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  • Dopant regions imaging in scanning electron microscopy

    Page(s): 043512 - 043512-7
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    An approach to the dopant profiling in bulk specimens with the scanning electron microscope is presented. It will be shown that it is possible to use backscattered electrons, or secondary electrons produced by backscattered electrons, to obtain two dimensional information about the dopant spatial distribution in Sb-implanted silicon. The role of sample preparation, boundary condition, beam energy, and detection strategy will be extensively discussed. Experimental observation and numerical simulation highlight the capability to achieve the sensitivity and spatial resolution required to describe the dopant distribution in the high-dose near-surface region of ultrashallow junctions. View full abstract»

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  • Secondary electron emission and photoemission studies on surface films of carbon nitride

    Page(s): 043513 - 043513-5
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    The secondary electron emission yield of fullerene, graphite, and diamondlike carbon after low-energy N2+ ion bombardment was studied for antimultipactor applications. Nitrogen incorporation into the carbon thin films decreases their secondary emission yield, contrary to the hydrogen or oxygen effect. Carbon nitride surface textured to a nanometric scale had the property of hindering secondary electron emission. Valence bands obtained from photoemission spectroscopy using synchrotron radiation were correlated with secondary electron emission measurements. Multipactor threshold power for carbon nitride was 7.5 kW. View full abstract»

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  • Transverse electric dominant intersubband absorption in Si-doped GaInAsN/GaAs quantum wells

    Page(s): 043514 - 043514-4
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    We report observation of transverse electric (TE) dominant intersubband absorption in Si-doped GaInAsN/GaAs multiple-quantum-well structures. The TE dominant absorption is believed to be caused by the incorporation of nitrogen and the associated nitrogen state. When the confinement is strong in narrow quantum wells, the ground state is pushed up, which enhances the interaction with nitrogen state and significantly changes the nature of the state. View full abstract»

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  • Enhancement and depression in second-order optical nonlinearity of Ba2TiGe2O8 in crystallized glass prepared in a high magnetic field

    Page(s): 043515 - 043515-4
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    A magnetic field of H=10 T was applied perpendicularly or parallel to the surface of the 30BaO.15TiO2.55GeO2 (BTG) glass during its crystallization, and the effect of the magnetic field on the crystal orientation and second-order optical nonlinearity of the Ba2TiGe2O8 crystals formed at the glass surface was examined. Compared with the sample prepared by conventional crystallization in zero magnetic field, the c-axis (polarization axis) orientation and second-harmonic intensity of the Ba2TiGe2O8 crystals at the surface were enhanced in the sample fabricated with the field perpendicular to the surface and, by contrast, were depressed in the sample fabricated with the field parallel to the surface. The present study indicates that the application of high magnetic fields during crystallization is a technique to control the crystal orientations and optical properties of BTG crystallized glasses. View full abstract»

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  • Spin-polarized transport in one-dimensional waveguide structures with spatially periodic electric fields

    Page(s): 043701 - 043701-3
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    We investigate theoretically spin-polarized transport in a one-dimensional waveguide structure under spatially periodic electric fields. Strong spin-polarized current can be obtained by tuning the external electric fields. It is interesting to find that the spin-dependent transmissions exhibit gaps at various electron momenta and/or gate lengths, and the gap width increases with increasing the strength of the Rashba effect. The strong spin-polarized current arises from the different transmission gaps of the spin-up and spin-down electrons. View full abstract»

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  • Electronic structure and optical properties of (ZnSe)n/(Si2)m (111) superlattices

    Page(s): 043702 - 043702-7
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    The electronic properties of (ZnSe)n/(Si2)m (111) superlattices (SLs) are investigated theoretically in order to clarify the general features of the zone-folding and the band-mixing effects in superlattices composed of an indirect-band-gap semiconductor (Si). The detailed electronic structure of (ZnSe)n/(Si2)m (111) SLs are studied with the range n=m=10–16, giving special attention to the role of the interface states at the Zn–Si and Se–Si polar interfaces. The presence of the electric field in the SL is totally ignored, i.e., “the zero-field model.” The degeneracy of the energy minima of the conduction band at the M point in the zinc-blende-type bulk material cannot be lifted by the zone-folding effects alone. The band-mixing effect through the interfaces between the two constituent materials plays an important role in determining the overall band lineup throughout the entire Brillouin zone. The states at the conduction- and valence-band edges are confined two dimensionally in the Si layers. Furthermore, we have found two interface bands in the lower and upper regions of the gap. The states of the lower interface band are located at the Zn–Si interface, while those of the upper interface band are located at the Se–Si interface. The energies of the interface states depend on the parameters representing the Zn–Si and Se–Si bond lengths and the valence-band discontinuity between ZnSe and Si, but the interface states do not disappear from the gap with reasonable choices of the parameters. The electronic structure of the superlattice turns out to be quite sensitive to the combination of the well and barrier layer thicknesses. This sensitivity suggests the possibility of designing suitable band structu- res for device applications. Furthermore, the absorption spectra of the superlattices are calculated and are found to be quite different from those of bulk ZnSe and Si but fairly close to their average. The electronic and optical properties suggest that superlattices composed of indirect-band-gap semiconductors offer great potential for application to optical devices. 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

Full Aims & Scope

Meet Our Editors

Editor
P. James Viccaro
Argonne National Laboratory