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Articles 28561 - 28590 of 36694

Full-Text Articles in Physical Sciences and Mathematics

Electron Transport Mechanism In Gan/Algan Hemt Structures, Si̇bel Gökden Jan 2003

Electron Transport Mechanism In Gan/Algan Hemt Structures, Si̇bel Gökden

Turkish Journal of Physics

The electron transport mechanism in GaN/AlGaN HEMT (High Electron Mobility Transistors) structures grown with MBE on sapphire substrate was investigated by using the temperature dependence of the Hall coefficient, resistivity, carrier density and Hall mobility. Hall measurements were carried out using Van der Pauw geometry. From the LO-phonon-scattering-limited component of the mobility, we obtain LO phonon energy \hbar \omega \approx 90 meV and the momentum relaxation time of \tau_{m} \approx 4 fs. Also, from the temperature dependence of the 2D carrier density, we obtain the donor activation energy E_{a} \approx 29 meV.

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Measuring The Prompt Atmospheric Neutrino Flux With Down-Going Muons In Neutrino Telescopes, Gabriele U. Varieschi Jan 2003

Measuring The Prompt Atmospheric Neutrino Flux With Down-Going Muons In Neutrino Telescopes, Gabriele U. Varieschi

Physics Faculty Works

No abstract provided.

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Measuring The Prompt Atmospheric Neutrino Flux With Down-Going Muons In Neutrino Telescopes, Graciela Gelmini, Paolo Gondolo, Gabriele Varieschi Jan 2003

Measuring The Prompt Atmospheric Neutrino Flux With Down-Going Muons In Neutrino Telescopes, Graciela Gelmini, Paolo Gondolo, Gabriele Varieschi

Physics Faculty Works

In the TeV energy region and above, the uncertainty in the level of prompt atmospheric neutrinos would limit the search for diffuse astrophysical neutrinos. We suggest that neutrino telescopes may provide an empirical determination of the flux of prompt atmospheric electron and muon neutrinos by measuring the flux of prompt down-going muons. Our suggestion is based on the consideration that prompt neutrino and prompt muon fluxes at sea level are almost identical.

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Discrete Velocity Fields With Explicitly Computable Lagrangian Law, Curtis D. Bennett, Craig L. Zirbel Jan 2003

Discrete Velocity Fields With Explicitly Computable Lagrangian Law, Curtis D. Bennett, Craig L. Zirbel

Mathematics, Statistics and Data Science Faculty Works

We introduce a class of random velocity fields on the periodic lattice and in discrete time having a certain hidden Markov structure. The generalized Lagrangian velocity (the velocity field as viewed from the location of a single moving particle) has similar hidden Markov structure, and its law is found explicitly. Its rate of convergence to equilibrium is studied in small numerical examples and in rigorous results giving absolute and relative bounds on the size of the second–largest eigenvalue modulus. The effect of molecular diffusion on the rate of convergence is also investigated; in some cases it slows convergence to equilibrium. …

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Inflation In A Flat Universe, Koray Karaca, Selçuk Bayin Jan 2003

Inflation In A Flat Universe, Koray Karaca, Selçuk Bayin

Turkish Journal of Physics

We started the evolution of a flat universe from a nonsingular state called prematter which is governed by an inflationary equation of state P=(\gamma -1)\rho , where \gamma represents the initial vacuum dominance of the universe. The evolution of the universe-except in the prematter era-is affected neither by the initial vacuum dominance nor by the initial expansion rate of the universe. On the other hand, present properties of the universe, such as the Hubble constant, age and density, are sensitive to the value of the temperature at the decoupling ( T_{m}) . Over a range between 3\cdot 10^{4}and 5\cdot 10^{4} …

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The Motion Of Cosmic Strings In The Schwarzschild Black Hole Spacetime, Sergey Roshchupkin, Yevgeniy Zinchenko Jan 2003

The Motion Of Cosmic Strings In The Schwarzschild Black Hole Spacetime, Sergey Roshchupkin, Yevgeniy Zinchenko

Turkish Journal of Physics

We study the classical dynamics of a bosonic string in the Schwarzschild spacetime using a perturbative scheme which is based on the assumption of a small value of a rescaled string tension parameter. The proposed approximation selfconsistently describes the string dynamics on the scale of large values for the worldsheet time in a fixed gauge.

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Multiply Charged Ions Produced After Deexcitation Processes For Important Elements In Astrophysics, Adel M. El-Shime, Adel A. Ghoneim, Yehia A. Lotfy Jan 2003

Multiply Charged Ions Produced After Deexcitation Processes For Important Elements In Astrophysics, Adel M. El-Shime, Adel A. Ghoneim, Yehia A. Lotfy

Turkish Journal of Physics

Selection random number method (Monte Carlo technique) is used to calculate the ion charge state distributions (CSD) and mean ion charge \bar{q} after K-, L_{I}, L_{III}- and M_{I}- shell ionization in neutral atoms and their q-fold ground state ions (q = 0 to 10) from C to Fe elements. Atomic data for radiative and non-radiative transitions and electron shake off process, which is used in the modeling vacancy cascade program, are computed with relativistic wave functions. Use of atomic data is important to accurately model vacancy cascades. To enhance the agreement between calculated and experimental values, the electron shake-off processes …

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Modeling Of Infrared Radiation For All Skies From Easy-To-Measure Meteorological Parameters At Tropical Location: Ilorin, Nigeria, Sunday O. Udo Jan 2003

Modeling Of Infrared Radiation For All Skies From Easy-To-Measure Meteorological Parameters At Tropical Location: Ilorin, Nigeria, Sunday O. Udo

Turkish Journal of Physics

Downward infrared radiation (L) and some easy-to-measure meteorological variables (relative humidity, clearness index and vapour pressure) were collected for a period of two years at Ilorin. Downward infrared radiation data were obtained using a pyrgeometer (Eppley-PIR), while data for relative humidity and vapour pressure for Ilorin were obtained from the Nigerian Meteorological Services, Lagos. Based on these data, using statistical regression analysis, empirical models (seven one-variable and nine two-variable) for predicting daily mean infrared radiation, from both clear and cloudy skies, were tested. Their advantage is that they only make use of easily measured meteorological parameters. The best one-variable model …

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Semi-Infinite Polarized Nuclear Matter With A Seyler-Blanchard Interaction, H. M. M. Mansour, Kh. A. Ramadan Jan 2003

Semi-Infinite Polarized Nuclear Matter With A Seyler-Blanchard Interaction, H. M. M. Mansour, Kh. A. Ramadan

Turkish Journal of Physics

The surface and curvature properties of semi-infinite polarized nuclear matter (SPNM) are calculated using a modified form of the Seyler-Blanchard potential. The level density parameter is extracted from the free energy using T^{2}-approximation. Good agreement is obtained between our calculations for the level density and other parameters which characterize the surface and curvature properties of SPNM and previous theoretical estimates. PACS number(s): 21.65.+f, 21.30.Fe

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Electrical Characteristics Of Si Doped With Sb By Laser Annealing, Raid A. Ismail, Aseel A. Hadi Jan 2003

Electrical Characteristics Of Si Doped With Sb By Laser Annealing, Raid A. Ismail, Aseel A. Hadi

Turkish Journal of Physics

Laser induced diffusion of antimony in silicon was obtained using a Nd:YAG pulsed laser. The irradiation of antimony-coated silicon by laser beam allowed melting and diffusion of antimony inside the silicon. Diodes were fabricated. Laser beam energy and substrate temperature played a major role in electrical sheet conductivity I-V, and C-V characteristics of the fabricated diodes. High laser energy reduced the electrical sheet conductivity and dominated the recombination current due to the generation-recombination process and trapping centers. On the other hand, the diffusion current dominated for diodes fabricated under heating conditions of the sample during laser irradiation. The C-V measurements …

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Microwave Signal Attenuation In Harmattan Weather Along Calabar-Akampkpa Line-Of-Sight Link, O. E. Eyo, A. I. Menkiti, Sunday O. Udo Jan 2003

Microwave Signal Attenuation In Harmattan Weather Along Calabar-Akampkpa Line-Of-Sight Link, O. E. Eyo, A. I. Menkiti, Sunday O. Udo

Turkish Journal of Physics

Line-of-sight (LOS) attenuation at 6.44GHz was measured at Calabar (4° 58' N, 8° 17' E) for ten months (Aug '93-May '94) using the Nigerian Telecommunications radio signal. The measurement was made with the intent of highlighting microwave signal attenuation in Harmattan weather conditions. The results are presented in terms of mean signal level and fog attenuation, fade rate distribution, fade depth distribution and scintillation index. The observed attenuation values due to Harmattan (fog) and the calculated (using Altshuler's model) are in fairly good agreement. Also, the statistics of fade distribution show fast fading of longer duration of the order of …

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Nuclear Matrix Elements Of Double Beta Decay In Deformed Nuclei, C. Selam, Atalay Küçükbursa, H. Bi̇rcan, H. A. Aygör, T. Babacan, İ. Maraş, A. Kökçe Jan 2003

Nuclear Matrix Elements Of Double Beta Decay In Deformed Nuclei, C. Selam, Atalay Küçükbursa, H. Bi̇rcan, H. A. Aygör, T. Babacan, İ. Maraş, A. Kökçe

Turkish Journal of Physics

Nuclear matrix elements (M_{GT}) for two-neutrino double beta transitions of selected nuclei were calculated via a QRPA approach by considering the charge-exchange spin-spin interactions in the particle-hole channel among nucleons. Calculations were performed for both spherical and deformed cases of nuclei. As a result of these calculations, it has been seen that, although the value of the nuclear matrix elements in deformation case are 2-4 times smaller when compared with that of the spherical case, it is still 2-8 times greater than the experimental values.

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Study Of The Structure And Some Physical Properties Of Sodium-Boro-Phosphate Glasses Containing Antimony And Iron Oxides, Karam Abdel-Aati̇ Ali, Ahmet Gamal El-Din Mostafa Jan 2003

Study Of The Structure And Some Physical Properties Of Sodium-Boro-Phosphate Glasses Containing Antimony And Iron Oxides, Karam Abdel-Aati̇ Ali, Ahmet Gamal El-Din Mostafa

Turkish Journal of Physics

Boro-phosphate glasses containing transition metal oxides are of special interest. Hence, some sodium-Boro-phosphate glasses containing iron and antimony oxides were prepared and investigated. The structural investigation indicated the presence of different borate groups as well as tetragonal phosphate units. Most of the iron cations were found to occupy the low spin Fe^{3 +} in the tetrahedral coordination state. It was observed that some antimony act as network former cations and some others act as bridges between any two adjacent polyhedra. At high antimony oxide content, the formation of some Sb-Fe bonds was also detected. The magnetic susceptibility measurements showed a …

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Extragalactic Objects In Basle Fields, Selçuk Bi̇li̇r, Yüksel Karataş, Serap Ak Jan 2003

Extragalactic Objects In Basle Fields, Selçuk Bi̇li̇r, Yüksel Karataş, Serap Ak

Turkish Journal of Physics

We discriminated between the extragalactic objects (galaxies and quasars) and stars for Basle star fields, Plaut I, SA 54, and SA 82 by comparing Basle fields and APS POSS I finder charts. Their numbers are 187, 70, and 93 for Plaut I, SA 54, and SA 82, respectively. Most of these objects are apparently faint in V, and they cause an overestimated local luminosity function for absolutely faint magnitudes, M(V) > 5. This effect is more conspicious for the field Plaut I.

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Microwave Rotational Components Of The \Nu_9= 1 And \Nu _{10} = 2 Vibrational Modes Of ^{13}Ch_{3}Cch Molecule In The Range 16 -- 50 Ghz, Mohammad Al-Share, J. A. Roberts Jan 2003

Microwave Rotational Components Of The \Nu_9= 1 And \Nu _{10} = 2 Vibrational Modes Of ^{13}Ch_{3}Cch Molecule In The Range 16 -- 50 Ghz, Mohammad Al-Share, J. A. Roberts

Turkish Journal of Physics

Some rotational components have been measured in the ground, the \nu _9 = 1 and the \nu _{10} = 2 vibrational states for ^{13}CH_3CCH isotopic species in the frequency range 16--50 GHz. A set of rotational constants has been determined, which gives the best fit between the observed and the calculated frequencies, for each vibrational state. A Fermi resonance was found between these two states.

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Studies On Some Lithium-Borate Glasses Containing Iron And Copper, G. A. Yahya Jan 2003

Studies On Some Lithium-Borate Glasses Containing Iron And Copper, G. A. Yahya

Turkish Journal of Physics

A lithium-borate-glass system containing iron and copper cations has been thoroughly investigated, in order to obtain information about the structural role of both the iron and copper in such glass hosts. The amorphous phase of the prepared glass samples was confirmed from their X-ray diffraction. From the infrared spectra it was concluded that the glass networks are highly deformed and boron appeared in both tri- and tetra-hedral coordination states as well as in some ring structure. As copper was introduced, replacing lithium, it acts as a network modifier only while the iron acts as network former (FeO_4). The molar magnetic …

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Photoelectrochemical Properties Of Cdse:Sb Thin Film Based Solar Cells: Influence Of Electrode Thickness, Elahipasha U. Masumdar, L. P. Deshmukh Jan 2003

Photoelectrochemical Properties Of Cdse:Sb Thin Film Based Solar Cells: Influence Of Electrode Thickness, Elahipasha U. Masumdar, L. P. Deshmukh

Turkish Journal of Physics

CdSe:Sb (0.1 mol%) thin films of varying thicknesses (423--1838 nm) have been deposited onto the glass and stainless steel substrates in an alkaline medium (pH = 10) using a solution growth technique. The photoelectrochemical activities of these films have been examined using CdSe:Sb (0.1 mol%)/0.25 M NaOH - 0.25M Na_2S- 0.25M S/graphite cell configuration. The films were characterized under illumination of 20 mW/cm^2} intensity to evaluate various cell parameters such as \eta, ff, R_s, R_{sh} etc. It is found that the efficiency \eta and fill factor ff increased from 0.24% to 0.45%, and 51% to 52.9%, respectively, with increase in …

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Electrical, Optical, Structural And Morphological Properties Of Nis Films, Ferhunde Atay, Sali̇h Köse, Vi̇ldan Bi̇lgi̇n, İdri̇s Akyüz Jan 2003

Electrical, Optical, Structural And Morphological Properties Of Nis Films, Ferhunde Atay, Sali̇h Köse, Vi̇ldan Bi̇lgi̇n, İdri̇s Akyüz

Turkish Journal of Physics

The electrical, optical, structural and morphological properties of NiS films are less studied than other materials such as CdS, CdTe, ZnS, ZnO, CdO etc. Our aim in this work is to deposit NiS films, examine some of their physical properties and investigate their suitability for photovoltaic devices. NiS films were deposited onto glass substrates at a substrate temperature of 300 \pm 5 °C using the ultrasonic spray pyrolysis (USP) technique. The variations of temperature-dependent conductivity under the conditions of light and dark were investigated and it was seen that illumination reduces conductivity. The activation energy for the doped region and …

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Null Membranes In Dyonic Black Hole Background, Alexandr Lelyakov, Sergey Nikolaevich Roshchupkin Jan 2003

Null Membranes In Dyonic Black Hole Background, Alexandr Lelyakov, Sergey Nikolaevich Roshchupkin

Turkish Journal of Physics

We consider null bosonic p-branes in curved spacetimes. The general solutions of the classical equations of motions and constraints for the null-membrane in four-dimensional dyonic black hole background are found.

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Decoherence In Two Coupled Qubits, Kristian Rabenstein, Dmitri V. Averin Jan 2003

Decoherence In Two Coupled Qubits, Kristian Rabenstein, Dmitri V. Averin

Turkish Journal of Physics

We have developed quantitative description of quantum coherent oscillations in the system of two coupled qubits in the presence of weak decoherence that in general can be correlated between the two qubits. It is shown that in the experimentally realized scheme of excitation of the oscillations, their waveform is not very sensitive to the magnitude of decoherence correlations. Modification of this scheme into potentially useful probe of the degree of decoherence correlations at the two qubits is suggested.

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Decoherence In Ballistic Mesoscopic Interferometers, Georg Seelig, Sebastian Pilgram, Markus Büttiker Jan 2003

Decoherence In Ballistic Mesoscopic Interferometers, Georg Seelig, Sebastian Pilgram, Markus Büttiker

Turkish Journal of Physics

We provide a theoretical explanation for two recent experiments on decoherence of Aharonov-Bohm oscillations in two- and multi-terminal ballistic rings. We consider decoherence due to charge fluctuations and emphasize the role of charge exchange between the system and the reservoir or nearby gates. A time-dependent scattering matrix approach is shown to be a convenient tool for the discussion of decoherence in ballistic conductors.

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Qce: A Simulator For Quantum Computer Hardware, Kristel Michielsen, Hans De Raedt Jan 2003

Qce: A Simulator For Quantum Computer Hardware, Kristel Michielsen, Hans De Raedt

Turkish Journal of Physics

The Quantum Computer Emulator (QCE) described in this paper consists of a simulator of a generic, general purpose quantum computer and a graphical user interface. The latter is used to control the simulator, to define the hardware of the quantum computer and to debug and execute quantum algorithms. QCE runs in a Windows 98/NT/2000/ME/XP environment. It can be used to validate designs of physically realizable quantum processors and as an interactive educational tool to learn about quantum computers and quantum algorithms. A detailed exposition is given of the implementation of the CNOT and the Toffoli gate, the quantum Fourier transform, …

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Adiabatic Quantum Pumping Of Coherent Electrons, Ora Entin-Wohlman, Amnon Aharony, Vyacheslavs Kashcheyevs Jan 2003

Adiabatic Quantum Pumping Of Coherent Electrons, Ora Entin-Wohlman, Amnon Aharony, Vyacheslavs Kashcheyevs

Turkish Journal of Physics

We review recent theoretical calculations of charge transfer through mesoscopic devices in response to slowly-oscillating, spatially-confined, potentials. The discussion is restricted to non-interacting electrons, and emphasizes the role of quantum interference and resonant transmission in producing almost integer values (in units of the electronic charge e) of the charge transmitted per cycle, Q. The expression for the pumped charge is derived from a systematic expansion of the system scattering states in terms of the temporal derivatives of the instantaneous solutions. This yields the effect of the modulating potential on the Landauer formula for the conductance in response to a constant …

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Quantum Computing With Electrons On Liquid Helium, İsmai̇l Karakurt Jan 2003

Quantum Computing With Electrons On Liquid Helium, İsmai̇l Karakurt

Turkish Journal of Physics

A quantum computer based on electrons floating over liquid helium is described. Each qubit is made of combinations of ground and first excited states of an electron trapped over micro-electrodes just below the helium surface. We describe mechanisms for preparing the initial state of the qubit, operations with the qubits, and a proposed readout. This system is, in principle, capable of \sim 10^4 operations in a decoherence time, the time in which the wave function collapses.

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Persistent Currents In Mesoscopic Loops And Networks, Igor O. Kulik Jan 2003

Persistent Currents In Mesoscopic Loops And Networks, Igor O. Kulik

Turkish Journal of Physics

The paper describes persistent (also termed ``permanent", or ``non-decaying") currents in mesoscopic metallic and macromolecular rings, cylinders and networks. The current arises as a response of system to Aharonov-Bohm flux threading the conducting loop and does not require external voltage to support the current. Magnitude of the current is periodic function of magnetic flux with a period of normal-metal flux quantum \Phi_0 = hc/e. Spontaneous persistent currents arise in regular macromolecular structure without the Aharonov-Bohm flux provided the azimuthal periodicity of the ring is insured by strong coupling to periodic background (a ``substrate"), otherwise the system will undergo the Peierls …

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Quantum State Generation And Entanglement Manipulation Using Linear Optics, Şahi̇n Kaya Özdemi̇r, Takashi Yamamoto, Masato Koashi, Nobuyuki Imoto Jan 2003

Quantum State Generation And Entanglement Manipulation Using Linear Optics, Şahi̇n Kaya Özdemi̇r, Takashi Yamamoto, Masato Koashi, Nobuyuki Imoto

Turkish Journal of Physics

Quantum information processing (QIP) requires unitary operations, measurements and synthesis, manipulation and characterization of arbitrary quantum states. Linear optics provides efficient tools for these purposes. In this review paper, we introduce the elements of linear optics toolbox, and briefly discuss some experimental and theoretical investigations using this toolbox. Our main focus will be the qubit state generation and entanglement extraction using linear optics toolbox.

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Mesoscopic D-Wave Qubits: Can High-T_C Cuprates Play A Role In Quantum Computing?, Alexandre M. Zagoskin Jan 2003

Mesoscopic D-Wave Qubits: Can High-T_C Cuprates Play A Role In Quantum Computing?, Alexandre M. Zagoskin

Turkish Journal of Physics

Due to nontrivial orbital pairing symmetry, surfaces and interfaces of high-T_c superconductors support states which violate time-reversal (T-) symmetry. Such naturally degenerate states, useful as working states of a qubit, are standard for atomic or molecular-size qubit prototypes (e.g. based on nuclear spins), but exceptional for mesoscopic qubits. (In particular, they hold promise of a better scalability.) In these lectures I review the physics of T-breaking on surfaces and interfaces of high-T_c superconductors; then describe existing proposals for high-T_c based qubits and the current state of experiments; finally, I discuss the decoherence sources in the system, open questions, and future …

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Preparation And Optimization Of High Quality Tin Films, Özlem Duyar, Cengi̇z Koçum, H. Zafer Durusoy Jan 2003

Preparation And Optimization Of High Quality Tin Films, Özlem Duyar, Cengi̇z Koçum, H. Zafer Durusoy

Turkish Journal of Physics

TiN thin films have been deposited by DC reactive magnetron sputtering method on glass substrates. The effects of the substrate temperature and the substrate bias voltage on the structural, optical and electrical properties of the films were studied by using XRD, STM, optical transmission and resistivity measurements. The bias voltage was varied in the 0 to 200 V range for two substrate temperatures, 100 °C and 300 °C. The results showed that the substrate bias voltage influenced the stoichiometry and structure of the films. The smoothest and least porous TiN films were prepared at about 160 V substrate bias voltage …

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Admittance And Impedance Spectroscopy On Cu(In,Ga)Se_2 Solar Cells, A. Sertap Kavasoglu, Habi̇be Bayhan Jan 2003

Admittance And Impedance Spectroscopy On Cu(In,Ga)Se_2 Solar Cells, A. Sertap Kavasoglu, Habi̇be Bayhan

Turkish Journal of Physics

The present work reports some experimental results on the electrical properties of high efficiency ZnO/CdS/Cu(In,Ga)Se_2 heterojunction solar cells. Admittance spectroscopy has been employed for characterisation of the bulk and interface levels in the absorber Cu(In,Ga)Se_2 layer. The temperature dependent capacitance-frequency analysis indicated an emission from a shallow acceptor like defect level with an activation energy of about 75 meV. Information on the equivalent circuit model of the devices has been provided by the analysis of impedance measurements. The impedance data are presented in the Nyquist plot at several dc bias voltages at 300 K. The equivalent circuit model consisting of …

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Structural, Electrical And Spectral Studies On Double Rare-Earth Orthoferrites La_{1-X}Nd_Xfeo_3, O.M. Hemeda, Mohsen Mohamed Barakat, D. M. Hemeda Jan 2003

Structural, Electrical And Spectral Studies On Double Rare-Earth Orthoferrites La_{1-X}Nd_Xfeo_3, O.M. Hemeda, Mohsen Mohamed Barakat, D. M. Hemeda

Turkish Journal of Physics

Samples of double rare-earth ferrite La_{1-x}Nd_xFeO_3 are synthesized by a high-temperature double sintering ceramic technique. X-ray diffraction shows that all compounds have an orthorhombic structure. The values of lattice parameter and the volume of the unit cell, changes with increasing Nd^{3+} content. The Goldschmidt tolerance factor decreases and goes far from unity with increasing Nd content. The samples containing Nd ions with x = 0.1, 0.2 and 0.3 have higher resistivity than that of LaFeO_{3}, but for x \ge 0.4 the resistivity decreases. The results indicate the presence of extrinsic semiconducting properties up to 100 °C above which the hopping …

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