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Energetics Of Spherical Clusters, Hati̇ce Kökten, Şaki̇r Erkoç
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 …
Fundamental Research And Device Technology, B. K. Ridley
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.
Electrons And Phonons In Gan Semiconductor Quantum Well Devices, M. Babiker, N. A. Zakhleniuk, C. R. Bennett, V. N. Stavrou, B. K. Ridley
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.
Electron Transport In Gaas Quantum Wells: Effect Of Interface Roughness Scatterin, Rita Gupta
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 …
Exchange-Correlation Effects In The Impurity-Limited Mobility Of Gaas Quantum Wires, B. Tanatar
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.
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
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 …
Large-Bandgap Semiconductors, B. K. Ridley
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.
Angular Dependence And Mode Distribution Of Acoustic Phonon Emission By Hot 2d Electrons In Gaas/Algaas Heterojunctions And Quantum Wells, Dietmar Lehmann, Czeslaw Jasiukiewicz
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 …
Electrons In Large-Bandgap Bulk Semiconductors And Quantum Wells, N. A. Zakhleniuk, M. Babiker, C. R. Bennett, B. K. Ridley
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.
Coherent Control Experiments As A Probe Of The Carrier Scattering Processes, P. Le Jeune, X. Marie, T. Amand, M. Paillard, J. Barrau
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.
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
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, …
Feasibility Of The Gainp/Ingaas/Gaas System For Modulation Doped Field-Effect Transistors, C. Besi̇kci̇, Y. Ci̇van
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 …
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
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 …
Novel Detectors And Lasers For Telecommunications, Anthony J. Vickers, Hamid R. Mashayekhi, Pattara Aiyarak, Diego Oriato
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 …
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
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 …
Silicon-Based Optoelectronics: Progress And Challenges, Tamim P. Sidiki, Clivia M. Sotomayor Torres
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.
3 \Mu M Intersubband Quantum Well Photodetector (Qwip), Rita Gupta, A. L. Y. Wong, S. K. Haywood
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. …
Hellish-Vcsel: A Hot Electron Laser, A. Obrien-Davies, N. Balkan, A. Boland-Thoms, M. J. Adams, J. Roberts
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 …
Single Si \Delta-Doped Gaas Investigations By New Photothermal Wavelength Modulated Photocurrent Technique, Fi̇kret Hajiev, Yener Özkan, M. Çeti̇n Arikan
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 …
Semiconductor And Dielectric Microcavity Spectroscopy, Ali̇ Serpengüzel
Semiconductor And Dielectric Microcavity Spectroscopy, Ali̇ Serpengüzel
Turkish Journal of Physics
Semiconductor and dielectric microcavities are used for the localization of photons as well as the enhancement of photon density of states. The enhancement of photoluminescence, electroluminescence, and lasing by the use of microcavities leads to novel active and passive optoelectronic and photonic devices such as channel droppping filters, semiconductor lasers, and resonant cavity enhanced devices. Experimental results showing photoluminescence enhancement in active planar, lasing in active ellipsoidal microcavities as well as light scattering in passive and spherical microcavities are presented.
Characterization Of Inas/Gaas Qd Structures By Hrem And Pl Spectroscopy, Y. Ati̇ci̇, D. Cherns, A. Polimeni, M. Henini, L. Eaves
Characterization Of Inas/Gaas Qd Structures By Hrem And Pl Spectroscopy, Y. Ati̇ci̇, D. Cherns, A. Polimeni, M. Henini, L. Eaves
Turkish Journal of Physics
No abstract provided.
Experimental Separation Of Phonon And Extrinsic Scattering In 2d Carrier Gases In Gaas, F. F. Ouali, H. R. Francis, H. C. Rhodes
Experimental Separation Of Phonon And Extrinsic Scattering In 2d Carrier Gases In Gaas, F. F. Ouali, H. R. Francis, H. C. Rhodes
Turkish Journal of Physics
A new method which separates phonon scattering from extrinsic scattering in 2D gases in GaAs is presented. In contrast to previous ones, the technique makes no assumptions about the temperature dependence of the extrinsic scattering. The preliminary measurements of the phonon limited mobility \mu_{ph} on two electron gas samples show a Bloch-Grüneisen regime in the temperature range 1.2-4.5K and the results agree reasonably well with other experimental and theoretical work.
Wigner Crystalization In Semiconductor Quantum Wires, I. Al-Hayek, B. Tanatar, M. Tomak
Wigner Crystalization In Semiconductor Quantum Wires, I. Al-Hayek, B. Tanatar, M. Tomak
Turkish Journal of Physics
We study the Wigner crystallization in semiconductor quantum wires within the density functional approach. As the density of electrons in quasi-one-dimensional structures is lowered, we find that the system favors the crystalline phase as envisioned by Wigner.
The Effect Of Non-Equilibrium Acoustic Phonons On The Tunnel Current In Gaas/Alas Superlattices, S. A. Cavill, F. F. Ouali, L. J. Challis, A. J. Kent, M. Henini, A. V. Akimov
The Effect Of Non-Equilibrium Acoustic Phonons On The Tunnel Current In Gaas/Alas Superlattices, S. A. Cavill, F. F. Ouali, L. J. Challis, A. J. Kent, M. Henini, A. V. Akimov
Turkish Journal of Physics
We present the first study of the effect of ballistic acoustic phonons generated by a heated metal film on the tunnel current in GaAs/AlAs superlattices. The phonon-induced increase of the tunnel current as a function of applied voltage has a maximum at a voltage that varies linearly with heater temperature both in zero and applied magnetic field. The behaviour is consistent with phonon-assisted tunnelling by stimulated phonon emission. The system acts as a phonon spectrometer in the < 1THz frequency region with a resolution of approximately 200 GHz.
Optimisation Of The Tunable Wavelength Hot Electron Light Emitter, Ali̇ Teke, Naci̇ Balkan
Optimisation Of The Tunable Wavelength Hot Electron Light Emitter, Ali̇ Teke, Naci̇ Balkan
Turkish Journal of Physics
We report on the optimization of the hot electron tunable wavelength surface light emitting device developed by us. The device consists of a p-GaAs, and n-Ga_{1-x}Al_xAs heterojunction containing an inversion layer on the p- side, and GaAs quantum wells on the n- side, and is referred to as HELLISH-2 (Hot Electron Light Emitting and Lasing in Semiconductor Heterojunction). The device utilises hot electron longitudinal transport and, therefore, light emission is independent of the polarity of the applied voltage. In order to optimise the operation of the device a theoretical model that calculates the tunnelling and the thermionic components of the …
Binding Energies Of Excitons In Symmetric And Asymmetric Coupled Double-Quantum Well Structures In A Magnetic Field, Esi̇n Kasapoğlu, Hüseyi̇n Sari, Yüksel Ergün, Sezai̇ Elagöz, Naci̇ Balkan, İsmai̇l Sökmen
Binding Energies Of Excitons In Symmetric And Asymmetric Coupled Double-Quantum Well Structures In A Magnetic Field, Esi̇n Kasapoğlu, Hüseyi̇n Sari, Yüksel Ergün, Sezai̇ Elagöz, Naci̇ Balkan, İsmai̇l Sökmen
Turkish Journal of Physics
The binding energy of excitons in the symmetric and asymmetric coupled double GaAs/Ga_{1-x}Al_xAs quantum wells is calculated by using variational approach. Results have been obtained as a function of the potential symmetry, the size of the quantum well, and the coupling parameter of the wells in the presence of a magnetic field applied parallel to the growth direction. The role of the asymmetric barriers, magnetic field, barrier and well width in determining the tunability of the excitonic binding parameters of the GaAs/Ga_{1-x}Al_xAs system is discussed.
Improvement In Electroabsorption And The Effect Of The Electric Field In The Tuneable Wavelength Converter, Hüseyi̇n Sari, Esi̇n Kasapoğlu, Yüksel Ergün, İsmai̇l Sökmen
Improvement In Electroabsorption And The Effect Of The Electric Field In The Tuneable Wavelength Converter, Hüseyi̇n Sari, Esi̇n Kasapoğlu, Yüksel Ergün, İsmai̇l Sökmen
Turkish Journal of Physics
The numerical results of the study of a novel wavelength converter which can be tuned with the application of an external field are presented. For this device, exciton binding energies, radiuses and the absorption coefficient are numerically analysed as a function of electric field. We showed that the interband transition energy and the overlap function between electron and hole changes abruptly when an electric field is applied. This phenomenon can be used the increase the change in the absorption coefficient and reduce the on-state transmission loss in electroabsorption modulators.
A Gainasp/Inp Vertical Cavity Surface Emitting Laser For 1.5 \Mu M Operation, R. Sceats, N. Balkan, M. J. Adams, J. Masum, A. J. Dann, S. D. Perrin, I. Reid, J. Reed, P. Cannard, M. A. Fisher, D. J. Elton, M. J. Harlow
A Gainasp/Inp Vertical Cavity Surface Emitting Laser For 1.5 \Mu M Operation, R. Sceats, N. Balkan, M. J. Adams, J. Masum, A. J. Dann, S. D. Perrin, I. Reid, J. Reed, P. Cannard, M. A. Fisher, D. J. Elton, M. J. Harlow
Turkish Journal of Physics
We present the results of our studies concerning the pulsed operation of a bulk GaInAsP/InP vertical cavity surface emitting laser (VCSEL). The device is tailored to emit at around 1.5 \mu m at room temperature. The structure has a 45 period n-doped GaInAsP/InP bottom distributed Bragg reflector (DBR), and a 4 period Si/Al_2O_3 dielectric top reflector defining a 3-\lambda cavity. Electroluminescence from a 16 \mu m diameter top window was measured in the pulsed injection mode. Spectral measurements were recorded in the temperature range between 125K and 240K. Polarisation, lasing threshold current and linewidth measurements were also carried out at …
An Investigation Of Electrical Properties Of Porous Silicon, G. Algün, M. Ç. Arikan
An Investigation Of Electrical Properties Of Porous Silicon, G. Algün, M. Ç. Arikan
Turkish Journal of Physics
In this work, electrical properties of porous silicon structures, formed with electrochemical anodization in HF acid solution under two different current densities, were investigated. In these experiments, Sb doped (111)-oriented n-type silicon samples with 0.006-0.015 \Omega cm resistivity was used. Samples were anodized in a solution of 38% HF and 99% C_2H_2OH at 1:1 ratio for 15 minutes. After anodization, the structures that formed at low current density (J = 5 mA/cm^2) was compared with structures that formed at high current density (J = 30 mA/cm^2). Both structures and electrical properties were investigated.