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Band Edge (band + edge)
Kinds of Band Edge Selected AbstractsDC conduction in bis(dimethylglyoximato)palladium(II) thin filmsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2007A. A. Dakhel Abstract Bis(dimethylglyoximato)palladium (II) complex thin films of polycrystalline structure were prepared by sublimation in a vacuum at 140°C on p-Si substrates. After carrying out the characterisation of the prepared films by X-ray diffraction and X-ray fluorescence methods, Al-complex-Si MIS devices were fabricated. The constructed MIS structure was characterised by measuring the capacitance as a function of gate voltage at 1 MHz. The dependence of dc-current density on gate voltage and temperature in the range of 293 - 328 K of the MIS device was measured. It was found that the experimental data follow the trap-charge-limited space-charge-limited conductivity mechanism, from which the total concentration and the exponential energy distribution of the trap density were determined. In general, the measured quantities suggest that the conduction can be realised by thermally assisted hopping between localised states bundled in a very narrow band lying energetically near the mobility band edge. Moreover, results show that it is possible to use a film of the complex in applications of low-k dielectric material. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoconduction and transport mechanisms in polycrystalline zincphthalocyanine thin filmsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2007S. Senthilarasu Abstract Zincphthalocyanine (ZnPc) thin films were prepared by the vacuum evaporation method under a pressure of 10 -6 mbar. The X-ray diffraction analysis of vacuum evaporated ZnPc films reveals that the structure of the films is polycrystalline in nature. The photoconduction properties have been studied in the wavelength range 400 ,800nm using suitable masks. The Photoconductivity of the films as a function of light intensity and applied voltage were studied and results were discussed in detail. The photoconduction was found to increase with higher light illumination and maximum at the band edge of the ZnPc thin film. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of substrate temperature on the properties of vacuum evaporated indium selenide thin filmsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2005C. Viswanathan Abstract Thin films of InSe were obtained by thermal evaporation techniques on glass substrates maintained at various temperatures (Tsb = 30°, 400°C). X-ray diffraction analysis showed the occurrence of amorphous to polycrystalline transformation in the films deposited at higher substrate temperature (400°C). The polycrystalline films were found to have a hexagonal lattice. Compositions of these films have been characterized by EDAX and the surface analysis by scanning electron microscopy. Optical properties of the films, investigated by using spectrophotometer transmittance spectra in the wavelength range (300 , 1100 nm), were explained in terms of substrate temperatures. Films formed at room temperature showed an optical band gap (Egopt) 1.56 eV; where as the films formed at 400°C were found to have a Egopt of 1.92 eV. The increase in the value of Egopt with Tsb treatment is interpreted in terms of the density of states model as proposed by Mott and Davis. The analysis of current -Voltage characteristics, based on space charge limited currents (SCLC) measurements, confirms the exponential decrease of density of states from the conduction band edge towards the Fermi level for both the amorphous and polycrystalline films. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis and characterization of a new disubstituted polyacetylene containing indolylazo moieties in side chainsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2006Zhen Li Abstract A new disubstituted polyacetylene with indolylazo moieties in its side chains (9) was synthesized by a post functionalization strategy, which was difficult, or perhaps impossible, to obtain from the direct polymerization of its corresponding monomer. The polymer is soluble in common solvents and thermally stable. The polymer shows good optical transparency with an absorption maximum at 393 nm and a band edge at ,530 nm. Its poled film exhibits a resonant d33 value of 17.9 pm/V and its optical nonlinearity is resistant to thermal decay at up to 147 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5672,5681, 2006 [source] Characterization of deep levels at GaAs/GaAs and GaAs/InAs interfaces grown by MBE-interrupted growth techniquePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2007M. Kaniewska Abstract In order to find the origin of crystalline defects occurring in the preparation of InAs/GaAs quantum dots (QDs), their appearance was tracked through three different sample types designed as Schottky diodes. Specimens with a GaAs cap layer on a GaAs buffer layer as well as with an InAs wetting layer without QDs were grown by molecular beam epitaxy (MBE) using the interrupted growth technique. Deep level transient spectroscopy (DLTS) was used for comparison with structures containing InAs QDs. It was found that two main levels with thermal activation energies of 0.14,0.16 eV and 0.46,0.52 eV from the conduction band edge, respectively, are grown-in defects, which are characteristic of the growth interrupted interface occuring under an excess of As. Both these levels together with an additional level at 0.10,0.12 eV found in the InAs wetting layer structures were also present in those with QDs, probably resulting from strain or In penetration. All three defects were agglomerated close to the interface created by the interrupted growth. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigation of the localization effect in InGaNAs/GaAs SQWs using the LSE modelPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2010Esmaeil Abdoli Abstract In this paper, the temperature behaviors of photoluminescence (PL) spectra of as-grown and annealed InGaASN/GaAs single quantum-well (SQW) samples with different nitrogen levels have been investigated by means of the localized-state ensemble (LSE) model. The variations of PL peak position and linewidth versus temperature are attributed to the creation of a fluctuation potential in the band edge of the host material from the nonuniform distribution of nitrogen in the structure. The anomalous thermal behaviors have been investigated by using the LSE model and a good agreement between experimental and theoretical results has been observed, especially at low temperature. The LSE model predicts a reduction of the localized states in rapid thermal annealed (RTA) samples compared to the as-grown state. [source] Comparison of deep level spectra in p-type and n-type GaN grown by molecular beam epitaxyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2007A. Armstrong Abstract Deep levels in n-type GaN:Si and p-type GaN:Mg grown by molecular beam epitaxy were compared using deep level optical spectrscopy (DLOS). For n-GaN, the major bandgap states were observed to lie within 1 eV of the valence band edge. For the p-type film, hole photoemission from deep levels at near the conduction band edge and electron photoemission from a deep level near the valence band edge were resolved. Overall, the p-GaN filmed incorporated nearly ten times greater deep level concentration. Bandgap states attributed to residual carbon impurities with large concentration were found near the minority band edge in both films. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Compositional dependence of optical and vibrational properties of strontium barium niobate (SrxBa1,xNb2O6)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2007C. David Abstract The index of refraction, the optical band edge and the Raman scattering of strontium barium niobate, SrxBa1,xNb2O6 with 0.38 < x < 0.77 have been studied. The ordinary refractive index does not depend on x, while the extra-ordinary one increases with increasing x. The band edge is almost unaffected by the Ba- or Sr-content and shows a weak band bowing. Both the index of refraction and the band edge may be used for an optical determination of the composition of the crystal. Raman spectra show the typical behavior of tungsten bronze type crystals with broad bands and complicated spectral shapes. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and characterization study of multidimensional hierarchical ZnO nanostructuresPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2007Dong Jun Park Abstract ZnO multidimensional hierarchical structure was successfully fabricated with the sequence of ZnO top layers/ZnO nanorods/ZnO buffer/Si(111) substrate by continuous controlling growth condition in metal organic chemical vapor deposition (MOCVD) system. Transmission electron microscopy (TEM) showed that ZnO nanorods in hierarchical structure had a single crystal hexagonal wurtzite structure with ,0001,ZnO growth direction. Only near band edge (NBE) emissions with very weak deep level emission are observed around 3.28 eV. This indicates that ZnO hierarchical structure grown by MOCVD shows a good optical quality and less interior defects. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Theory of electronic structure of BGaAs and related alloysPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2008A. Lindsay Abstract Previous experiments on BxGa1,xAs containing a few percent boron show a dramatic increase in electron effective mass, m*e, similar to that observed in many GaNxAs1,x samples. By contrast, there is a near-linear blue-shift of the energy gap, which can be conventionally described using the virtual crystal approximation. We use a tight-binding model to show that isolated B atoms have little effect either on the band gap or lowest conduction band dispersion in BxGa1,xAs. By contrast, B pairs and clusters introduce defect levels close to the conduction band edge (CBE) which, through a weak band-anticrossing (BAC) interaction, significantly reduce the band dispersion in and around the , -point, thus accounting for the strong increase in m*e and reduction in mobility observed in these alloys. Calculations show that replacing gallium by aluminium shifts the CBE upwards, leading to a large density of B-related states in the energy gap. By contrast, indium shifts the band edge downwards, leading eventually to a band edge m*e close to that predicted by the virtual crystal approximation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Time-resolved spectroscopy in an undoped GaN (1-101)PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008Eunhee Kim Abstract Time-resolved photoluminescence spectroscopy was performed at 77 K in a GaN (1-101) grown on a 7 degree off-axis (001) Si substrate. The sample was grown by metal-organic-vapour-phase-epitaxy (MOVPE) and was un-intentionally doped with O, C and Si. By using photoluminescence intensity correlation method, the energy relaxation process of the photogenerated carriers near the band edge was investigated in pico-second regime. The correlation signal was represented by a single exponential decay curve and the energy relaxation time was determined, which depended strongly on the kinetic energy of the excess carriers. At low energies, the relaxation time was around 700 ps, while it was as short as a few ps at the highest energy under study. The correlation signals obtained for carriers of which kinetic energy was less than 80 meV showed an anti-correlation behaviour suggesting the occurrence of carrier accumulation. The time constants for the accumulation were of several picoseconds depending on the kinetic energy, which was nearly equal to the decay time constants determined at high energies. This fact shows that the energy relaxation at high energies is controlled by the emission of an LO phonon. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Composition control of ZnSSeO quaternary alloys grown on GaPPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006Y. Nabetani Abstract ZnSSeO quaternary alloys were grown on GaP substrates by molecular beam epitaxy and the group VI compositions were controlled. Reductions of the supply amounts of Se and S both increase the O concentration. S concentration were decreased by the decrease of S supply and increased by the decrease of Se supply. ZnSSeO alloys lattice-matched to GaP were obtained with high O and S concentrations. Dominant peaks were observed at the near band edge in the photoluminescence spectra. The band gap energies were shifted according to the group VI compositions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A theory of nonlinear susceptibility in polaritonic band-gap materials doped with multi-level atomsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2005D. Mukherji Abstract We have studied the nonlinear susceptibility in dispersive polaritonic band-gap (DPBG) materials in the presence of five-level impurity atoms. Initially, the atom is prepared in a coherent superposition of two levels |b, and |c,. The levels |b, and |c, are coupled to the upper level |a, with a coherent laser field. The nonlinear susceptibility has been calculated corresponding to transitions |a, , |c, and |a, , |b, using the equation of motion for the density matrix. The atomic system is interacting with the polariton reservoir. The effect of atom-polariton reservoir coupling on the imaginary part of the nonlinear susceptibility has been studied when the resonance energy lies in lower band of the polariton spectrum. It is found that by shifting the resonance energy away from the band edge, the system goes to the probe gain state. It is also found that by changing the intensity of the coherent laser field, the system switches from gain to loss state and vice-versa. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoreflectance study of the electronic structure of Si-doped InyGa1,yAs1,xNx films with x < 0.012PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005Y.-S. Kang Abstract The electronic structure of Si-doped InyGa1,yAs1,xNx films on GaAs substrates, grown by nitrogen-plasma-assisted MBE, was examined by photoreflectance (PR) spectroscopy at temperatures between 20 K and 300 K. The measured critical-point energies were described by a band anti-crossing (BAC) model with the addition of a Burstein-Moss band-filling term. The energy difference between the nitrogen impurity level and conduction band edge was (0.3004 ± 0.0101) eV at 20 K, and (0.3286 ± 0.0089) eV at 295 K; the BAC interaction parameter was (2.588 ± 0.071) eV. It was inferred from the magnitude of the Burstein-Moss shift that the near-surface carrier concentration, probed by PR, is reduced from the bulk (Hall effect) carrier concentration by a reduction factor of 0.266 ± 0.145. The effect of strain on the PR energies was too small to observe. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis and Characterization of Bulk, Vitreous Cadmium Germanium ArsenideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2009Bradley R. Johnson Cadmium germanium diarsenide glasses were synthesized in bulk form (,2.4 cm3) using procedures adapted from the literature. Several issues involved in the fabrication and quenching of amorphous CdGexAs2 (x=0.45, 0.65, 0.85, and 1.00, where x is the molar ratio of Ge to 1 mol of Cd) are described. An innovative processing route is presented to enable fabrication of high-purity, vitreous, crack-free ingots with sizes up to 10 mm diameter, and 30,40 mm long. Specimens from selected ingots were characterized using thermal analysis, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, particle-induced X-ray emission, Rutherford backscattering, secondary ion mass spectrometry, X-ray diffraction, density, and optical spectroscopy. Variations in properties as a function of processing conditions and composition are described. Results show that the density of defect states in the middle of the band gap and near the band edges can be decreased three ways: through suitable control of the processing conditions, by doping the material with hydrogen, and by increasing the concentration of Ge in the glass. [source] Dual-band-rejection filter based on split ring resonator (SRR) and complimentary SRRMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2009Xin Hu Abstract A novel concept of a compact, low insertion-loss dual-band-rejection filter (DBRF) is proposed, and its equivalent circuit model is given. The filter consists of single split ring resonators (SRRs) on the top of the host microstrip line and Complimentary SRR etched on the back ground plane. The dimensions of the structure are as small as 1.4 cm × 2 cm, while high frequency selectivity is achieved at both band edges due to the presence of two transmission zeros. The filter has an insertion loss of better than 1 dB, a return loss of larger than 10 dB in the passband from 3.3 to 4.0 GHz, and two rejections of greater than 30 dB within 2.5,2.6 and 5.2,5.6 GHz. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2519,2522, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24596 [source] A hybrid functional scheme for defect levels and band alignments at semiconductor,oxide interfacesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2010Peter Broqvist Abstract We introduce a theoretical scheme to study defect energy levels and band alignments at semiconductor,oxide interfaces. The scheme relies on hybrid functionals to overcome the band gap underestimation typically achieved with semilocal density functionals. For atomically localized defects, the more accurate description achieved with hybrid functionals does not lead to significant shifts of the charge transition levels, provided these levels are referred to a common reference potential. This result effectively decouples the shifts of the band edges with respect to the defect levels. We also show that relative shifts of conduction and valence band edges as determined by exact nonlocal exchange lead to band offsets in excellent agreement with experimental values for several semiconductor,oxide interfaces. The proposed scheme is illustrated through a series of applications, including the dangling bond defects in silicon and germanium, the charge state of the O2 molecule during silicon oxidation, and the oxygen vacancy in Si,SiO2,HfO2 stacks. [source] Numerical simulations of photon trapping in doped photonic crystals doped with multi-level atomsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2005Mahi R. Singh Abstract A theory of photon trapping has been developed in photonic band-gap (PBG) and dispersive polaritonic band-gap (DPBG) materials doped with an ensemble of five-level atoms. These materials have gaps in their photon energy spectra. The atoms are prepared as coherent superpositions of the two lower states and interact with a reservoir and two photon fields. They also interact with each other by dipole-dipole interaction. The Schrödinger equation and the Laplace transform method are used to calculate the expressions for the number densities of the atomic states. Numerical simulations for a PBG material reveal that when the resonance energies lie away from the band edges and within the lower or upper bands, trapping is observed at certain values of the relative Rabi frequency associated with the two fields, which vary depending on the strength of the dipole-dipole interaction between the atoms. Also, if the photon fields are held constant, the population densities of the excited states of the atoms increase with increasing dipole-dipole interaction. These are very interesting phenomena. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||