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1999

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On The Coronal Activity Of The Rs Cvn-Type Binaries, Osman Demi̇rcan, Hasan Ak Jan 1999

On The Coronal Activity Of The Rs Cvn-Type Binaries, Osman Demi̇rcan, Hasan Ak

Turkish Journal of Physics

We re-analysed the behaviour of coronal activity of the RS CVn-type binaries as a function of stellar and orbital parameters. Highly significant correlations were found between the x-ray luminosity L_x and the stellar radius R, the Roche lobe filling fraction \Gamma, and the Alfven radius RA. The correlations of L_x with the mass M, the absolute magnitude M_V, the surface gravity g, the Roche lobe filling fraction \Gamma, and the Alfven radius RA are likely to be due to correlations of these quantities with the stellar radius R. Surprisingly, no correlation of L_x on the color (B-V), the rotation velocity …

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Co-Ordinated Multi-Wavelength Observations Of The Rs Cvn System Cf Tuc, Edwin Budding, K. L. Jones, O. B. Slee, L. Watson Jan 1999

Co-Ordinated Multi-Wavelength Observations Of The Rs Cvn System Cf Tuc, Edwin Budding, K. L. Jones, O. B. Slee, L. Watson

Turkish Journal of Physics

A `multi-site, multi-wavelength' campaign on the eclipsing RS CVn binary CF Tuc was carried out in 1996 over both optical (photometry and spectroscopy) and radio (microwave) ranges. The microwave data was taken with the Australia Telescope Compact Array (ATCA). It covered slightly more than one complete orbital cycle at 4.8 and 8.64 GHz in one continuous run. There was also coverage of about 25% of the light curve at 1.38 and 2.38 GHz. High dispersion spectroscopy was obtained using the McLellan 1m telescope and échelle spectrograph at Mt John University Observatory (New Zealand). Supporting photometry came from various smaller-scale facilities …

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Cover And Contents Jan 1999

Cover And Contents

Turkish Journal of Physics

No abstract provided.

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The Experimental Studies On Zr Photoelectron Spectra, I. Buribayev, N. A. Nurmatov, N. Talipov Jan 1999

The Experimental Studies On Zr Photoelectron Spectra, I. Buribayev, N. A. Nurmatov, N. Talipov

Turkish Journal of Physics

Photoelectron spectra (PES) taken from crystalline Zr at 8.4 eV and 10 eV have been studied by a high resolution photoelectron analyzer, with \Delta E = 0.1 eV, and the results were compared to the results calculated for electron density of states in the valence band. Photoelectron work function (WF) measured from the atomically clean Zr surface by Fowler isothermal curves was found to be 3.95 eV \pm 0.02 eV. It was shown that a small dose of residual gas, namely CO, absorbed on the Zr surface, resulted in a decrease of the WF by 0.15-0.25 eV as well as …

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The Structure Of Liquid Alkali Metals Calculated By The Thermodynamic Perturbation Theory, H. Bi̇rtan Kavanoz, İdri̇s Gümüş Jan 1999

The Structure Of Liquid Alkali Metals Calculated By The Thermodynamic Perturbation Theory, H. Bi̇rtan Kavanoz, İdri̇s Gümüş

Turkish Journal of Physics

The structure of a hard sphere fluid has been calculated numerically via the Percus-Yevick (PY) and hypernetted-chain (HNC) closure relations and used as a reference system to calculate the structure of liquid alkali metals under the optimized random-phase approximation (ORPA) using the effective ion-ion pair potential formed by the Heine-Abarenkov (HA), and the empty-core (EC) pseudopotentials. The results are compared with experimental results. The calculations made by the reference system under the HNC closure relation are in better agreement with experimental results than those found under the PY closure relation.

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The Lattice Dynamics Of \Gamma-Iron, Kemal Çolakoğlu, G. Uğur, M. Çakmak, H. M. Tütüncü Jan 1999

The Lattice Dynamics Of \Gamma-Iron, Kemal Çolakoğlu, G. Uğur, M. Çakmak, H. M. Tütüncü

Turkish Journal of Physics

Lattice dynamical calculations are performed on \gamma-iron using the Clark-Gazis-Wallis (CGW) model to represent the ion-ion interactions, and a modified form of the Sharma-Joshi model to include ion-electron interactions. The theory is used to compute the phonon dispersion curves, frequency spectra and the lattice specific heat of \gamma-iron. The obtained results are in good agreement with the experimental findings, and are better than those calculated using the other theories.

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Ionizing Radiations And Annealing Influence On Mosfet Charge States, Zainabidinov Ciragiddin, Atamuratov Atabek, Ysupov Akhmed, Adinaev Kuvondik Jan 1999

Ionizing Radiations And Annealing Influence On Mosfet Charge States, Zainabidinov Ciragiddin, Atamuratov Atabek, Ysupov Akhmed, Adinaev Kuvondik

Turkish Journal of Physics

The threshold voltage shift \Delta V_T and its components due to trapped-oxide charges \Delta V_{Not} and Si-SiO_2 interface traps \Delta V_N in MOSFET exposed to Bremsstrahlung, Co_{60} irradiation and annealing were studied. Several effects caused by differences in the photon energies from two types of sources are discussed as well as a mechanism of changing the trapped-oxide and Si-SiO_2 interface traps by annealing. The mechanism is based on previously available models.

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Determination Of Partial Coordinate Number Of Atoms In Amorphous Yb-As-S(Se, Te) Systems, Rasi̇m Ali̇-Zade, Eldar Efendi̇yev, Elman Haji̇yev Jan 1999

Determination Of Partial Coordinate Number Of Atoms In Amorphous Yb-As-S(Se, Te) Systems, Rasi̇m Ali̇-Zade, Eldar Efendi̇yev, Elman Haji̇yev

Turkish Journal of Physics

Partial coordinate number for amorphous compounds, consisting three type of atoms has been determined by way of calculation of the radial distribution curve maximum. The equation solution method has been used as algorithm in programme, which writed in FORTRAN language for working in IBM compatible computers. The programme is compact and integable. The programme has been used for determination partial coordinate number of ytterbium atom in amorphous compounds- YbAs_2S_4, Yb_3As_4S_9, YbAs_4Te_7, Yb_3As_4Se_9 YbAs_4Se_7. Real value of partial coordinate number of ytterbium in this compunds is 2 or 3.

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Calibration Of Millimetric Marmara Radio Telescope And Radio Detection Of Ozone Line Over Gebze/Kocaeli In Turkey, Mehmet Emi̇n Özel, I. M. Yusifov, A. O. Allakhverdiev, A. A. Vertiy, G. Bayer, Osman Demi̇rcan, H. Kirbiyik, T. Adigüzel Jan 1999

Calibration Of Millimetric Marmara Radio Telescope And Radio Detection Of Ozone Line Over Gebze/Kocaeli In Turkey, Mehmet Emi̇n Özel, I. M. Yusifov, A. O. Allakhverdiev, A. A. Vertiy, G. Bayer, Osman Demi̇rcan, H. Kirbiyik, T. Adigüzel

Turkish Journal of Physics

A brief description of the calibration procedures for the millimetric Marmara Radio Telescope, MRT-2 is presented. Observations carried out during the spectroscopic calibration work is indicative of daily variations of Ozone line of sight density over the telescope location. This being also the first radio observations carried out in Turkey, a short account of observations and results are given.

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Magnetodielectrical Polymer Compositional Materials, Sh. V. Mamedov, Y. Lenger, Sevi̇l Bolcal, Vilayet A. Alekperov, M. A. Ramazanov, R. Z. Sadikhov Jan 1999

Magnetodielectrical Polymer Compositional Materials, Sh. V. Mamedov, Y. Lenger, Sevi̇l Bolcal, Vilayet A. Alekperov, M. A. Ramazanov, R. Z. Sadikhov

Turkish Journal of Physics

Magnetodielectrical polymer compositional materials containing carbonyl iron (CI) were obtained. The changes of permittivity and permeability, loss angle tangent, resistivity, mechanical and electrical properties, depending on the content of carbonyl iron have been investigated. It is shown that the magnetodielectrical materials with 20-40% mass content of carbonyl iron have possible practical use.

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Energetics Of Spherical Clusters, Hati̇ce Kökten, Şaki̇r Erkoç Jan 1999

Energetics Of Spherical Clusters, Hati̇ce Kökten, Şaki̇r Erkoç

Turkish Journal of Physics

The energetics of spherical clusters of elements Fe in bcc, Ca and Pb in fcc, and C in diamond structure have been investigated by using emprical many-body potential energy function which contains two- and three-body inteactions. In the variation of average interaction energy per atom (E_b) versus cluster size (N_{sh}; number of shells) only carbon clusters have magic numbers at 5, 8, 11 and 14 shells. E_b versus N_{sh} becomes smooth after 15 shells for carbon, however this variation becomes smooth for the other elements after 10 shells. The variation of two-body to three-body interaction energy versus cluster size becomes …

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Cover And Contents Jan 1999

Cover And Contents

Turkish Journal of Physics

No abstract provided.

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Fundamental Research And Device Technology, B. K. Ridley Jan 1999

Fundamental Research And Device Technology, B. K. Ridley

Turkish Journal of Physics

Highlights of the interaction between fundamental research and semiconductor device technology are summarized.

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Electrons And Phonons In Gan Semiconductor Quantum Well Devices, M. Babiker, N. A. Zakhleniuk, C. R. Bennett, V. N. Stavrou, B. K. Ridley Jan 1999

Electrons And Phonons In Gan Semiconductor Quantum Well Devices, M. Babiker, N. A. Zakhleniuk, C. R. Bennett, V. N. Stavrou, B. K. Ridley

Turkish Journal of Physics

Electrons and polar optical phonons and their interactions are considered in the context of semiconductor quantum well devices, with particular reference to real quantum well laser structures. Distinction is made between wide-barrier and narrow-barrier structures and we explore the implications of these regimes for the description of the electron capture process. Special emphasis is made on the significant effects arising from the large effective mass ratio in AlN/GaN structures.

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Electron Transport In Gaas Quantum Wells: Effect Of Interface Roughness Scatterin, Rita Gupta Jan 1999

Electron Transport In Gaas Quantum Wells: Effect Of Interface Roughness Scatterin, Rita Gupta

Turkish Journal of Physics

The importance of interface roughness (IFR) scattering of electrons and LO-phonons for electron transport in semiconductor quantum wells is discussed. Modulation doping of quantum wells minimizes the effect of impurity scattering on the low-field electron mobility so that IFR scattering of electrons in the well becomes the major limiting factor. A model calculation of IFR scattering of electrons in quantum wells is presented and it is shown that (both)\Lambda and \Delta, the parameters defining IFR, can be estimated by comparing the theoretical and experimental electron mobilities. The application of high electric field leads to a distribution of hot electrons which …

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Exchange-Correlation Effects In The Impurity-Limited Mobility Of Gaas Quantum Wires, B. Tanatar Jan 1999

Exchange-Correlation Effects In The Impurity-Limited Mobility Of Gaas Quantum Wires, B. Tanatar

Turkish Journal of Physics

We study the many-body effects described by the local-field corrections on the mobility of quasi-one dimensional electron systems. The low temperature mobility due to remote-impurity doping and interface-roughness scattering is calculated within the relaxation time approximation. We find that correlation effects significantly reduce the mobility at low density.

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Well-Width Dependence Of Warm Electron Relaxation And Interface Roughness Scattering In Gaas/Ga_{1-X}Al_Xas Multiple Quantum Wells, M. Cankurtaran, H. Çeli̇k, E. Tiraş, A. Bayrakli, N. Balkan Jan 1999

Well-Width Dependence Of Warm Electron Relaxation And Interface Roughness Scattering In Gaas/Ga_{1-X}Al_Xas Multiple Quantum Wells, M. Cankurtaran, H. Çeli̇k, E. Tiraş, A. Bayrakli, N. Balkan

Turkish Journal of Physics

We review our recent results concerning the well-width dependence of the acoustic-phonon-assisted energy relaxation of two-dimensional (2D) warm electrons in modulation-doped GaAs/Ga_{1-x}Al_xAs multiple quantum wells. Electron energy-loss rates via the emission of acoustic phonons are determined from the amplitude of Shubnikov-de Haas (SdH) oscillations, measured as a function of lattice temperature and applied electric field. Experimental results are compared with the existing theoretical models that involve deformation-potential and screened and unscreened piezoelectric scattering. Well-width dependence of the quantum and transport mobilities of 2D electrons in the same samples have also been determined by measuring the quantum oscillations in both the …

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Large-Bandgap Semiconductors, B. K. Ridley Jan 1999

Large-Bandgap Semiconductors, B. K. Ridley

Turkish Journal of Physics

The general features of large-bandgap semiconductors that make them interesting for electronic and optoelectronic applications are briefly reviewed. The nitrides AIN, GaN and InN are singled out for a more focused treatment.

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Angular Dependence And Mode Distribution Of Acoustic Phonon Emission By Hot 2d Electrons In Gaas/Algaas Heterojunctions And Quantum Wells, Dietmar Lehmann, Czeslaw Jasiukiewicz Jan 1999

Angular Dependence And Mode Distribution Of Acoustic Phonon Emission By Hot 2d Electrons In Gaas/Algaas Heterojunctions And Quantum Wells, Dietmar Lehmann, Czeslaw Jasiukiewicz

Turkish Journal of Physics

We report a detailed theoretical study of the angular dependence and mode distribution of the acoustic phonon emission by hot two-dimensional electron gases in GaAs/AlGaAs heterojunctions and quantum wells and compare the results with some recent heat pulse measurements for carrier temperatures below 50 K. Common to all the experimental results was the strong dependence of the ratio of emitted longitudinal acoustic (LA) phonons to transverse acoustic (TA) phonons from the width of the quantum well and the absence of LA phonons propagating in a direction close to the 2DEG normal for GaAs/AlGaAs heterojunctions. To explain these phenomena and to …

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Electrons In Large-Bandgap Bulk Semiconductors And Quantum Wells, N. A. Zakhleniuk, M. Babiker, C. R. Bennett, B. K. Ridley Jan 1999

Electrons In Large-Bandgap Bulk Semiconductors And Quantum Wells, N. A. Zakhleniuk, M. Babiker, C. R. Bennett, B. K. Ridley

Turkish Journal of Physics

The analytical theory of hot electrons interacting with lattice vibrations, impurities, and interface roughness in quantum wells is developed. We have obtained new distribution functions which describe all the kinetic properties of the non-equilibrium electron gas. As a specific example we present the electric field dependence of the electron mobility in GaN-based quantum wells and in bulk GaN. The relative importance of the different scattering mechanisms is analysed in detail.

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Coherent Control Experiments As A Probe Of The Carrier Scattering Processes, P. Le Jeune, X. Marie, T. Amand, M. Paillard, J. Barrau Jan 1999

Coherent Control Experiments As A Probe Of The Carrier Scattering Processes, P. Le Jeune, X. Marie, T. Amand, M. Paillard, J. Barrau

Turkish Journal of Physics

We report on coherent control experiments of excitons in GaAs/AlGaAs Quantum wells.This technique, which relies on the linear response of the crystal,is used to investigate the spin-dependent exciton-exciton scattering.

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Energy Relaxation Rate Of Hot Electrons In N-Type Gan Epilayers Using Heat Pulse Techniques, P. Hawker, A. J. Kent, T. S. Cheng, C. T. Foxon Jan 1999

Energy Relaxation Rate Of Hot Electrons In N-Type Gan Epilayers Using Heat Pulse Techniques, P. Hawker, A. J. Kent, T. S. Cheng, C. T. Foxon

Turkish Journal of Physics

We have measured the energy relaxation rate of hot electrons in MBE grown bulk GaN epilayers on GaAs and sapphire substrates over the electron temperature range 1 - 130 K. The measurements were made using heat pulse techniques. For layers grown on GaAs substrates the results show that the carriers reside in the substrate, probably as in a GaAs/AlGaAs heterojunction. For layers grown on sapphire substrates we obtain a P \propto T^4_e dependence for the relaxation rate in the low temperature limit, consistent with piezoelectric coupling in the so-called `dirty' regime, changing to a linear dependence in the high temperature, …

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Feasibility Of The Gainp/Ingaas/Gaas System For Modulation Doped Field-Effect Transistors, C. Besi̇kci̇, Y. Ci̇van Jan 1999

Feasibility Of The Gainp/Ingaas/Gaas System For Modulation Doped Field-Effect Transistors, C. Besi̇kci̇, Y. Ci̇van

Turkish Journal of Physics

Si-doped single Ga_{0.51}In_{0.49}P layers and GaInP/InGaAs/GaAs modulation doped field-effect transistor structures grown by gas source molecular beam epitaxy were characterized in detail through Hall-Effect and Deep Level Transient Spectroscopy techniques. Electrical characterization of the undoped and moderately Si-doped (N_D = 3 x 10^{17} cm^{-3}) GaInP layers yielded an electron trap with an activation energy of 0.75 eV and a temperature dependent capture cross section with a capture barrier of 0.593 eV showing DX center properties. The trap was not detected in highly Si doped (N_D = 4 x 10^{18} cm^{-3}) as grown layers suggesting that it is a defect complex …

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Giant Efficiency Of Fröhlich Interaction In Self-Assembled Quantum Dots, A. W. E. Minnaert, A. Yu. Silov, J. E. M. Haverkort, J. H. Wolter, A. Garcia, V. N. Gladilin, V. M. Fomn, J. T. Devreese Jan 1999

Giant Efficiency Of Fröhlich Interaction In Self-Assembled Quantum Dots, A. W. E. Minnaert, A. Yu. Silov, J. E. M. Haverkort, J. H. Wolter, A. Garcia, V. N. Gladilin, V. M. Fomn, J. T. Devreese

Turkish Journal of Physics

A transition is being observed from an inhomogeneously broadened photoluminescence band under non-resonant excitation of InAs/GaAs Self-Assembled quantum Dots (SAD's) into up to five phonon-assisted emission bands under selective excitation. A similar effect is obtained from photoluminescence excitation experiments (PLE). We interpret the phonon-assisted PL as being due to a giant efficiency of the Fröhlich interaction between an exciton polarized by strain in the SAD and LO-phonons. The model is consistent with the pronounced p-type polarization of the emission observed in our cleaved-side PL-measurements. Further support is obtained from our calculations in which a different localization of the electrons and …

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Novel Detectors And Lasers For Telecommunications, Anthony J. Vickers, Hamid R. Mashayekhi, Pattara Aiyarak, Diego Oriato Jan 1999

Novel Detectors And Lasers For Telecommunications, Anthony J. Vickers, Hamid R. Mashayekhi, Pattara Aiyarak, Diego Oriato

Turkish Journal of Physics

For the most part the field of optoelectronics has been dominated by the pn junction for both detector and laser applications. This domination will probably hold true for laser applications for many more years although the simple forward biased junction may be challenged by other novel approaches as increased complexity is required such as multi-wavelength emission, wavelength conversion, and Thz operation. The first real novel use of the pn junction was developed by Balkan et al. [1]. Their HELLISH device paved the way for novel approaches in the use of the pn junction. In this paper I shall introduce another …

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Butt-Coupling Loss Of 0.1 Db/Interface In Inp/Ingaas Multi-Quantum-Well Waveguide-Waveguide Structures Grown By Selective Area Chemical Beam Epitaxy, C. A. Verschuren, M. R. Leys, H. Vonk, J. H. Wolter, P. J. Harmsma, Y. S. Oei Jan 1999

Butt-Coupling Loss Of 0.1 Db/Interface In Inp/Ingaas Multi-Quantum-Well Waveguide-Waveguide Structures Grown By Selective Area Chemical Beam Epitaxy, C. A. Verschuren, M. R. Leys, H. Vonk, J. H. Wolter, P. J. Harmsma, Y. S. Oei

Turkish Journal of Physics

The lateral coupling of waveguiding structures in both [011] and [0\bar{1}1] directions is studied using embedded selective area epitaxy by Chemical Beam Epitaxy. All growth steps are carried out under the same growth conditions on (100) lnP substrates misoriented by 0.5° towards (111)B. Both planar and selectively grown material exhibits bright luminescence and narrow PL line widths (8 meV FWHM at 4K), up to the lateral junction. Moreover, no degradation of the original material properties is observed after regrowth. SEM images show very flat layers and excellent lateral coupling for all four types of junctions. After reactive ion etching of …

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Silicon-Based Optoelectronics: Progress And Challenges, Tamim P. Sidiki, Clivia M. Sotomayor Torres Jan 1999

Silicon-Based Optoelectronics: Progress And Challenges, Tamim P. Sidiki, Clivia M. Sotomayor Torres

Turkish Journal of Physics

We review the status of silicon-based optoelectronics with emphasis on light emitting diodes. Erbium-doped Si, por-Si and silicon-based superlattices and nanostructures are discussed. The origin behind light emission in silicon with feature sizes below about 60 nm still remains poorly understood.

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3 \Mu M Intersubband Quantum Well Photodetector (Qwip), Rita Gupta, A. L. Y. Wong, S. K. Haywood Jan 1999

3 \Mu M Intersubband Quantum Well Photodetector (Qwip), Rita Gupta, A. L. Y. Wong, S. K. Haywood

Turkish Journal of Physics

In recent years photodetectors operating in the mid- to far infrared region of 3-15 \mu m have been designed based on electron and hole intersubband transitions in multiple quantum wells and superlattices. In general, QWIPs based on electron transitions show greater detectivity compared to the hole-based photodetectors. However, selection rules for electron intersubband transitions usually forbid the TE mode operation, associated with normal light incidence; Therefore, special coupling structures/geometries have been employed to couple light into the device. The spectral region 3-5 \mu m is of interest for a variety of applications such as environmental gas sensing, thermal imaging etc. …

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Hellish-Vcsel: A Hot Electron Laser, A. Obrien-Davies, N. Balkan, A. Boland-Thoms, M. J. Adams, J. Roberts Jan 1999

Hellish-Vcsel: A Hot Electron Laser, A. Obrien-Davies, N. Balkan, A. Boland-Thoms, M. J. Adams, J. Roberts

Turkish Journal of Physics

Hot Electron Light emission and Lasing In Semiconductor Heterostructures (HEL-LISH-1) is a novel hot electron surface emitter consisting of a GaAs QW on the n side of an Ga_{1-x}Al_xAs p-n junction. It utilises hot electron transport parallel to the junction plane. The injection of hot electron hole pairs into the QW is achieved via tunnelling and thermionic emission processes. Recently this structure has been modified by the incorporation of an upper and lower DBR defining a VCSEL (HELLISH-VCSEL). This has been shown to lase at room temperature with a Full Width at Half Maximum (FWHM) of 1.5 nm. In this …

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Single Si \Delta-Doped Gaas Investigations By New Photothermal Wavelength Modulated Photocurrent Technique, Fi̇kret Hajiev, Yener Özkan, M. Çeti̇n Arikan Jan 1999

Single Si \Delta-Doped Gaas Investigations By New Photothermal Wavelength Modulated Photocurrent Technique, Fi̇kret Hajiev, Yener Özkan, M. Çeti̇n Arikan

Turkish Journal of Physics

New Photothermal Wavelength Modulated Photocurrent (PWMPC) technique is reported. This technique is used for investigation of the MBE grown p-GaAs sample in which a single Si-layer was embedded with a \delta-type profile. Two spectral features were observed at 1.5137 eV and 1.5115 eV at 20 K. These peaks were attributed to the (D°,X) and (A°,X)-excitons bound to neutral donors and acceptors, respectively. We studied the temperature dependence of these excitonic peaks positions at temperatures between 20-90 K. Additionally, we demonstrate a blue shift of photocurrent spectra under a low level illumination intensity. PWMPC technique and the nature of the registered …

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