bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lattice Dynamical Investigations on DX Center Localised Vibrational Modes in AlxGa1−xAs and AlxGa1−xAs:Si
Authors: Pothiraj R. , Ramachandran K. 
Published: July 2007

AbstractLocalised vibrational modes (LVMs) associated with DX centers in AlxGa1−xAs and n‐type AlxGa1−xAs are worked out from a molecular model, introducing the relaxation. Preliminary studies indicate that some of the basic features observed from deep level transient spectroscopy (DLTS) can be viewed from the present calculations.
Compound‐Source MBE for ZnSe‐Based Lasers
Authors: Ohkawa K. , Takeishi H. , Hayashi S. , Yoshii S. , Tsujimura A. , Karasawa T. , Mitsuyu T. 
Published: July 2007

AbstractCompound‐source molecular beam epitaxy (CSMBE) for ZnSe‐based lasers is developed. This method employs compound sources instead of elemental sources. The ZnCdSe/ZnSSe/ZnMgSSe separate confinement heterostructure is grown by this method. Continuous‐wave operation of the device by CSMBE at room temperature is demonstrated.
Second Harmonic Generation in Thin Film II–VI Optical Waveguides
Authors: Wagner H. P. 
Published: July 2007

AbstractThe absolute values and dispersion of the second harmonic generation (SHG) coefficient of the cubic wide‐gap II–VI semiconductors Zn Te, ZnSe, and ZnS are investigated within the spectral range from 1047 to 1321 nm. The fundamental beam is generated by a Nd:YLF laser and by a tunable KTP optical‐parametric oscillator (OPO) pumped by a ps‐Ti:sapphire laser system. The measured values of the SHG coefficient are significantly higher than in commercially used birefringent crystals as KDP or ADP. In a further step symmetric single crystalline ZnSe/ZnTe/ZnSe/GaAs(001) waveguides are grown by metalorganic vapour phase epitaxy (MOVPE). Using end‐fire coupling a strong phasematched signal of the 1170.5 nm fundamental wave is observed. Phase matching is achieved by coupling the TE0 fundamental mode to the TM2 second harmonic mode.
Electrical Contacts to p‐ZnSe Based on HgSe and ZnTe
Authors: Einfeldt S. , Behringer M. , Nürnberger J. , Heinke H. , Behr T. , Becker C. R. , Hommel D. , Landwehr G. 
Published: July 2007

AbstractLow resistance ohmic contacts to p‐ZnSe involving the use of HgSe are studied in detail. HgSe does not form an ohmic contact with p‐ZnSe because of a residual valence band offset at the heterojunction of 0.5 to 0.6 eV. Annealing of HgSe/ZnSe:N does not result in an ohmic contact because a large miscibility gap in Hg1−xZnxSe prevents a HgZn interdiffusion and therefore the formation of a graded heterojunction. The molecular beam epitaxial (MBE) growth of Hg1−xZnxSe does not circumvent this problem because these epitaxial layers suffer from a compositional phase separation due to spinodal demixing during MBE growth. A significant improvement of HgSe based contacts could be achieved by the use of ZnSe1−xTex:N transition layers between HgSe and ZnSe:N. Either by abrupt, graded, or multilayer heterojunctions, very low contact resistivities are obtained. The growth of ZnSe1−xTex:N layers on top of ZnSe:N is shown to reduce the carrier concentration in ZnSe:N by several orders of magnitude. A nitrogen diffusion process is believed to be responsible for this effect.
(Dark Line Defects, Bright Line Lasers)‐Microscopic Studies of Single‐Shot Lasing in CdSe Quantum Wells
Authors: O'Donnell K. P. , Bagnall D. M. , Wright P. J. , Cockayne B. 
Published: July 2007

AbstractA preliminary report on single quantum well (SQW) lasers of CdSe grown by metalorganic vapour phase epitaxy (MOVPE) in a matrix of ZnSe is presented. The total device thickness is 3 μm. The quantum wells are „ultrathin”︁ in the range from 0.5 to 2 monolayers (ML). The time‐integrated spectra of spontaneous emission from the top surface of as‐grown samples are compared with spontaneous and stimulated edge emission from cleaved laser cavities. Such temporally and spatially integrated spectra are contrasted with single‐shot laser spectra obtained by adapting a 1 m single monochromator to operate as a videospectrograph. In addition to „hidden”︁ mode structure, the spectrograms reveal the strongly heterogeneous character of laser emission from these samples: bright lines that indicate materials of good quality are found adjacent to dark lines where the emission is weak or absent.
High‐Brightness Blue‐Green Light‐Emitting Diodes on ZnSe Substrates
Authors: Harsch W. C. , Cantwell G. , Schetzina J. F. 
Published: July 2007

AbstractHigh‐brightness blue and green light‐emitting diodes (LEDs) are produced based on homoepitaxial films grown by molecular beam epitaxy (MBE) on high quality ZnSe substrates. The substrates are grown by the Eagle‐Picher, seeded physical vapor transport (SPVTTM) technique. The substrates are twin‐free and contain no low‐angle grain boundaries. Double‐crystal X‐ray diffraction rocking curve studies yield a FWHM 〈400〉 = 11″ to 16″, indicating a crystal quality comparable to that of GaAs substrates. The blue LEDs produce 327 μW (10 mA, 3.2 V), with the light output sharply peaked at 489 nm, and exhibit an external quantum efficiency of 1.3%. The green LEDs produce 1.3 mW (10 mA, 3.2 V) peaked at 512 nm, corresponding to an external quantum efficiency of 5.3%.
Compton Profile of Ag2O
Authors: Bandyopadhyay S. , Saha S. K. , Chatterjee A. , Chatterjee A. K. 
Published: July 2007

AbstractThe Compton profile (CP) of polycrystalline silver oxide is measured with the use of 59.54 keV γ‐radiation from a 241Am source. The experimental data are compared with the renormalized free atom (RFA) model calculation using Watson's +1 well solution for the oxygen 2p state. Oxygen 2p6 and hybridization of different 4d–5s configurations of Ag are considered in the theoretical calculations. The theoretical values from such calculations agree well with experimental results.
Self‐Consistent Study of Lattice Relaxation around a Magnesium Impurity in Aluminium
Authors: Thiagarajan M. , Iyakutti K. , Palaniyandi E. 
Published: July 2007

AbstractThe lattice relaxation around a Mg impurity in an Al cluster is studied self‐consistently, using the MSXα method. The atoms surrounding the Mg impurity in an Al cluster are allowed to relax to various extents and the correponding total energies of the cluster are computed. It is found that for a particular relaxed position, the cluster total energy is minimum. For the Mg impurity in Al, the corresponding relaxation is found to be 4% of the lattice constant.
Lamb shift for an excitonic molecule
Authors: Ivanov A. L. , Haug H. 
Published: July 2007

AbstractA theory of the optical decay and of the resonant two‐photon creation of an excitonic molecule (xx) in direct band gap semiconductors is given within the polariton picture. An xx Schrödinger equation which includes both the Coulombic exciton‐exciton attraction and the polariton coupling is derived and analyzed. The solution of this equation describes an xx as the quasibound two‐polariton complex. The real and imaginary parts of the xx energy give self‐consistently the inverse xx radiative lifetime Γxx and the radiative renormalization Δxx of the xx energy (the xx Lamb shift), respectively. For 3D (CuCl) the polariton effects result in a non‐parabolic xx dispersion with M → ∞ at zero momentum; for quasi‐2D (GaAs) they lead to a “Mexican hat” structure in the xx dispersion at small momenta together with a considerable increase of both the xx effective binding energy ϵxx and lifetime Γxx. For quasi‐ID the influence of the polariton effects is so strong that an xx can exist only as a broad resonance (ϵxx ∼ Γxx).
Capture of carriers into a GaAs/AlGaAs quantum well relevance to laser performance
Authors: Haverkort J. E. M. , Blom P. W. M. , van Hall P. J. , Claes Hall J. , Claes J. , Wolter J. H. 
Published: July 2007

AbstractAn experimental and theoretical study of the carrier capture time into a semiconductor quantum well is presented. Oscillations of the phonon emission induced capture time are experimentally observed and good agreement with theory is found. The calculations show that not only the LO‐phonon emission induced capture time (ph‐capture) oscillates as a function of well width, but also the carrier–carrier scattering induced capture time (c‐c capture) oscillates by more than one order of magnitude as a function of the active layer design. Recently it has been shown that the carrier capture time is directly related to the modulation band width in a quantum well laser. As a result, it might be possible to tailor the modulation band width by optimizing the capture efficiency using a proper design of the active layer in a quantum well laser.
Dynamics of screening and field fluctuations on ultrashort time scales
Authors: Manzke G. , Henneberger K. , Heeg J. , El Sayed K. , Schuster S. , Haug H. 
Published: July 2007

AbstractThe short‐time dynamics of screening in semiconductors is considered after excitation with an ultrashort laser pulse of several 10 fs. While the kinetics of carriers is considered within standard approximations (semiconductor Bloch equations) the plasmon kinetics includes particularly memory effects due to non‐Markovian behaviour and retardation as well as interaction between plasmons and the coherent interband polarization induced by the laser pulse. For pulses shorter than the relaxation time of carriers pronounced oscillations of the plasmon density (intensity of plasma oscillations) are found which are strongly enhanced by the coherent interband polarization. It is concluded that the notion of plasmons as quasiparticles fails on an ultrashort time scale, because it is essentially an adiabatic concept and experiments in the fs‐domain should be reinterpreted in this respect.
Microscopic theory of the dephasing of coherent optical phonons due to anharmonic decay in polar semiconductors
Authors: Wenschuh U. , Schäfer W. , Zimmermann R. 
Published: July 2007

AbstractThe dephasing of coherent longitudinal optical phonons due to anharmonic decay is investigated from a microscopic point of view. Time‐resolved coherent anti‐Stokes Raman signals are calculated for GaP on the basis of a full phonon dispersion calculation and the relevant decay channels are identified and compared. Anharmonic renormalization effects in the phonon spectrum and their influence on the dephasing signals are investigated. Non‐Markovian dynamics of dephasing are calculated for GaP and result in a 30% faster dephasing signal than the corresponding Markovian dynamics.
Build‐up and decoherence of optical transients in disordered semiconductors
Authors: Velický B. , Kalvová A. 
Published: July 2007

AbstractFor a model two‐band semiconductor with static disorder, suddenly illuminated by intense light, the averaged non‐equilibrium Green function can be obtained within the coherent potential approximation. Explicit solutions found previously are analyzed on numerical examples of the transient photoexcited distribution. The results are used to test the semigroup property of the propagators and the analogous factorization of the particle correlation function known as the generalized Kadanoff‐Baym ansatz. Both properties hold much better if quasiparticle states are used instead of the bare particles. The quasiparticle modification of the ansatz is motivated formally and verified on numerical data.
Homogeneous linewidths of excitons in high and low band gap Ga0.52In0.48P
Authors: Grossmann P. , Feldmann J. , Göbel E. O. , Thomas P. , Arent D. J. , Bertness K. A. , Olson J. M. 
Published: July 2007

AbstractPhotoluminescence and picosecond four‐wave‐mixing experiments are reported on Ga0.52In0.48P grown by organometallic vapor phase epitaxy on GaAs substrates. The spectral behavior of the homogeneous linewidth in the range of the inhomogeneously broadened band gap excitonic resonance is found to be different for a high band gap as compared to a low band gap structure. Whereas the former shows the normal alloy behavior, the behavior of the low band gap sample supports the assumption that its structure consists of ordered domains with varying degrees of order. This means in particular that the main origin of the inhomogeneous broadening is different for the high and low band gap cases.
Dynamics of charge separation in type‐II hetero‐nipi‐structures after interband excitation
Authors: Hauenstein H. M. , Moritz N. , Seilmeier A. 
Published: July 2007

AbstractA subpicosecond light pulse creates carriers in the GaAs quantum wells of a type‐II GaAs/Al0.3Ga0.7As hetero‐nipi‐structure. Relaxation is monitored via transient absorption changes which reflect band‐filling effects and a decrease of the internal electric field. Thermionic emission of electrons to n‐doped AlGaAs layers is observed which proceeds within several hundred picoseconds. On a time scale reaching from several hundred microseconds to seconds nonexponential interband carrier recombination is found which strongly depends on the density of excited carriers. The time‐resolved data are discussed taking into account the complex band structure changes during the relaxation process in self‐consistent Thomas Fermi approximation.
Vibrational properties of thin films of ultraheavily doped semiconductors
Authors: Alvarado F. L. Castillo , Urbaniak‐Kucharczyk A. 
Published: July 2007

AbstractThe pseudospin model for the G1−xPx semiconductor alloy is considered in the coherent potential approximation. The phonon density of states in ultraheavily doped semiconductor thin films is investigated as a function of impurity concentration and the position of a monatomic layer inside the film. The obtained results show the dependence of the local density of states on the surface conditions.
Influence of rings on the electronic structure of lattices with topological defects
Authors: Lazo E. , Glass B. 
Published: July 2007

AbstractThe influence of rings on the electronic structure of open and closed lattices, like the Bethe and Husimi lattices, respectively, is studied. In both lattices topological defects are introduced changing, in alternating form, the number of nearest neighbors on each site. In the Bethe lattice with or without topological defects the local density of states has the symmetry of a central ring, but topological defects generate a gap in the electronic structure and some bound states in between. In the Husimi model formed with rings of two different numbers of sides, it is found that the electronic bands are symmetrical, if and only if, combinations of rings with even number of sides, independent of the presence of topological defects, are considered. In addition, gaps appear when alternating topological defects are introduced.
The Comparative Studies of Low‐Temperature Nearest‐Neighbour Distances in Alkali Hydride Crystals
Authors: Tyutyunnik V. I. 
Published: July 2007

AbstractThe numerical analysis demonstrates that at low temperatures the change in lattice parameter between the alkali hydride salts is related only to the difference between the radii of the “alkali atoms” which have the same sizes as those in the alkali metals with body‐centred cubic structure. There is no isotope effect on the size of particles constituting an alkali hydride crystal.
Brillouin Zone Centre Lattice Dynamical Studies of Nd2CuO4, Pr2CuO4, and Gd2CuO4
Authors: Amrithraj Mona , Devarajan V. 
Published: July 2007

AbstractBrillouin zone centre lattice dynamical studies for the tetragonal phase of the electron superconductors Nd2CuO4, Pr2CuO4, and Gd2CuO4 are reported for three potential models viz., short‐range valence force model, rigid ion model, and a polarizable ion model. The models are developed in three stages with the number of parameters increasing at every stage. The calculated TO‐LO frequencies and high‐frequency dielectric tensor values are compared with recent experimental values reported in the literature and the agreement is found to be very good. The eigenvectors for some of the modes are depicted.
The g‐Tensor Theory Based on the Single‐Determinant‐Basis Crystal‐Field Method
Authors: Zhou Kang‐Wei , Yang Jian‐Hua 
Published: July 2007

AbstractThe g‐tensor theory of the single‐determinant‐basis (SDB) crystal‐field method which has been published recently is developed. With such an SDB method a unified calculation of both the optical spectrum and EPR parameters of any d5 complex can be carried out in general. It is shown that the g‐value (being isotropic) of a cubic d5 complex decreases with decreasing average orbital reduction factor N for given Dq but increases with decreasing |Dq| for given N and that g is exactly a function of (Dq)2 for |Dq| < 1000 cm−1 and that g also decreases with increasing |ζ| for given B, C, and Dq. The application of the SDB method to Mn2+ ions in CaF2 and KZnF3 shows that not only the calculated optical spectra and the zero‐field splittings but also the g‐values are in good agreement with the findings. The calculated g‐values are, respectively, 2.00203 and 2.00194, while the findings are 2.0010 ± 0.0005 and 2.0021. Since it diagonalizes the electrostatic interaction, the crystal‐field, and the spin‐orbit coupling energies simultaneously, the SDB method can be extended to cases of arbitrary crystal‐field intensity, i.e., to arbitrary transition series.
Electron States of a Vacancy in the Core of the 90° Partial Dislocation in Silicon
Authors: Marklund S. , Wang Yong‐Liang 
Published: July 2007

AbstractAn LCAO scheme (linear combination of atomic orbitals) taking into account ten atomic orbitals (s‐, p‐, and d‐type) is used to calculate the electronic structure of a vacancy present in the core of the reconstructed 90° partial dislocation in silicon. The levels in the band gap are extracted using Lanczos' algorithm and a continued fraction representation of the local density of states. The three‐fold degenerate state of the ideal vacancy is split into three levels with energies 0.26, 1.1, and 1.9 eV measured from the valence band edge.
Electric and Photoelectric Properties of High Porosity Silicon
Authors: Kǔoka J. , Fejfar A. , Pelant I. 
Published: July 2007

AbstractThe basic problems of porous silicon (PS) transport, like long time constants, ageing, and the influence of contacts are discussed. The results of the steady‐state and transient photoconductivity on the self‐supporting p‐ and n‐type PS are presented and the resulting conclusions, related to the microstructure isotropy, trapping, and time‐dependent electric field redistribution are summarized. On the basis of the dark I–U characteristics and their temperature dependencies the different volume and surface transport mechanisms are discussed. The compatibility of the models of explanation of the strong PS photoluminescence with our transport results is discussed.
Thermally Induced Modifications in the Porous Silicon Properties
Authors: Halimaoui A. , Campidelli Y. , Larre A. , Bensahel D. 
Published: July 2007

AbstractVarious porous silicon (PS) properties are significantly modified by thermal annealing. For example, when a freshly prepared sample is annealed at 450°C, there are a significant reduction of the photoluminescence (PL) intensity, a change in the optical constants (refractive index and absorption coefficient), a sharp decrease in the material strain, hydrogen desorption, and change in the microstructure. The modification of all the parameters listed above (strain, PL, absorption coefficient, microstructure etc.) occurred for annealing temperatures between 350 and 450°C, and that is the same temperature range at which hydrogen is desorbed from the PS surface. The relationship between these parameters and the results of this comparison are discussed.
Core Shell Spectroscopy of Rapidly Oxidised Porous Silicon. Linking the Chemical and Electronic Structure
Authors: Bancert U. , Gardelis S. , Hamilton B. , Pettifer R. 
Published: July 2007

AbstractHigh resolution scanning transmission electron microscopy (STEM) and synchrotron X‐ray excitation of luminescence (XEOL) is used to probe the chemical nature of the luminescence mechanisms of porous and rapidly oxidised porous silicon. It is concluded that for fresh porous silicon, Si‐Si bonded material is involved in the luminescence. For oxidised material this is probably not the case, the chemical environment being SiO2.
From Porous Silicon to Clustered Matrices: A Comparison of Local Structures
Authors: Bayliss S. C. , Zhang Q. , Hutt D. A. 
Published: July 2007

AbstractStudies have been made of the local atomic structure ofclustered and porous silicon nanostructures, with the object of obtaining more information on the environments which exist in highly PL‐efficient material. In some structures the Si environments can be interpreted in terms of a small crystalline core surrounded by configurationally disordered material. Finally, although the details of the individual mechanisms responsible for the emission appear to be different for clustered and porous material, the overall behaviour can be linked t o the sizes and dimensionality of the units involved.
Transport Properties of Siloxene
Authors: Rosenbauer M. , Höpner A. , Dettlaff‐Weglikowska U. , Stutzmann M. 
Published: July 2007

AbstractThe transport properties of siloxene (as‐grown and annealed) are investigated. The dark conductivity is thermally activated with an activation energy of about 1 eV for as‐prepared siloxene, in accordance with the insulating nature of this material and its energy gap of about 2.6 eV. The conductivity is very sensitive to the presence of ambient gases. The spectral and temperature dependence of photo‐ conductivity is also discussed.
Anodized Amorphous Silicon: Present Status
Authors: Bustarret E. , Ligeon M. , Rosenbauer M. 
Published: July 2007

AbstractThe results of the few groups which have attempted to etch chemically or electrochemically amorphous silicon films prepared in various ways are reviewed briefly with a focus on the photoluminescence of such layers. The particular case of plasma‐deposited boron‐doped hydrogenated amorphous silicon subjected to an anodization in HF solutions followed by an electro‐oxidation in water is elucidated. Many similaritics between the properties of these materials and those of their crystalline counterparts are emphasized, but one significant difference between the resonantly excited PL spectra of the two porous materials is pointed out.
Si/CaF2 Superlattices. A Direct Gap Structure Due to Interface State Coupling
Authors: Ossicini Stefano , Fasolino A. , Bernardini F. 
Published: July 2007

AbstractOne promising approach for the development of silicon‐based light‐emitting devices is the epitaxial growth of Si nanostructures. In this context, the lattice matched system CaF2/Si/CaF2 as prototype of a well controlled and ordered Si‐based system with known microscopic structure is proposed. For this system, a new mechanism is found leading to a direct band gap based on the coupling of interface states in very thin Si layers.
Exciton Energies as a Function of Electric Field in Quantum Wells Finite Potential Barrier Case
Authors: Feng Yuan‐Ping , Spector H. N. 
Published: July 2007

AbstractA previous variational calculation of the exciton binding energy as a function of electric field in a semiconducting quantum well structure using a 3D hydrogenic trial wave function is extended to the case where the confining potential barrier is finite in height. The results are compared with those obtained for the same case using a 2D hydrogenic trial wave function. The results yield larger exciton binding energies for wide wells and strong electric fields. It is found that the crossover between 2D and 3D behavior occurs at a critical well width which is of the order of the exciton Bohr radius in zero field and which decreases with increasing electric field. It is also found that decreasing the height of the barrier decreases the binding energy of the exciton, as expected.