Browsing by Subject "Semiconductor quantum wires"

Now showing 1 - 13 of 13

Open Access
Characteristic equations for the lasing Modes of infinite periodic chain of quantum wires
(IEEE, 2008-06) Byelobrov, V. O.; Benson, T. M.; Altıntaş, Ayhan; Nosich, A.I.
In this paper, we study the lasing modes of a periodic open optical resonator. The resonator is an infinite chain of active circular cylindrical quantum wires standing in tree space. Characteristic equations for the frequencies and associated linear thresholds of lasing are derived. These quantities are considered as eigenvalues of specific electromagnetic-field problem with "active" imaginary part of the cylinder material's refractive index - Lasing Eigenvalue Problem (LEP). ©2008 IEEE.
Open Access
Confined optical phonon effects on the band gap renormalization in quantum wire structures
(Elsevier Science, 1999) Bennett, C. R.; Güven, K.; Tanatar, Bilal
We consider the different approximations for the bandgap renormalization (BGR) within the random phase approximation (RPA), the quasi-static limit and the plasmon-pole approximation, and compare with the full result. We then include bulk optical phonons and also the phonon confinement using the phonons from the dielectric continuum (DC) model. We show that the results are very similar except at low densities where the quasi-static results overestimate the renormalization.
Open Access
Coulomb drag effect in parallel cylindrical quantum wires
(Pergamon Press, 1996) Tanatar, Bilal
We study the Coulomb drag rate for electrons in two parallel quantum wires. The double-quantum wire structure is modeled for a GaAs material with cylindrical wires having infinite potential barriers. The momentum transfer rate between the wires (Coulomb drag effect) is calculated as a function of temperature for several wire separation distances. We employ the full wave vector and frequency dependent random-phase approximation (RPA) at finite temperature to describe the effective interwire Coulomb interaction. We find that the drag rate at high temperatures (i.e., T ≥ EF/2) is dominated by the collective modes (plasmons) of the system similar to the case in double-well structures. Including the local-field effects in an approximate way we estimate the importance of intrawire correlations to be significant. Copyright © 1996 Published by Elsevier Science Ltd.
Open Access
Dynamical screening effects in hot-electron scattering from electron-hole plasma and LO-phonon modes in quantum wires
(Elsevier, 1996) Bennett, C. R.; Tanatar, Bilal; Constantinou, N. C.
We present a fully dynamical and finite temperature study of the hot-electron momentum relaxation rate and the power loss in a coupled system of electron-hole plasma and bulk LO-phonons in a quantum wire structure. Interactions of the scattered electron with neutral plasma components and phonons are treated on an equal footing within the random-phase approximation. Coupled mode effects substantially change the transport properties of the system at low temperatures. Particularly, the "plasmon-like" and "LO-phonon-like" excitations yield comparable rates which, as a consequence of the singular nature of the ID density of states, can be large at the threshold. This is in contrast to room temperature results where only the LO-phonon mode contributes significantly to the rate. The density and temperature dependence of the power loss reveals that dynamical screening effects are important, and energy-momentum conservation cannot be satisfied above a certain density for a given initial energy.
Open Access
Exchange-correlation effects in the impurity-limited mobility of GaAs quantum wires
(Sci Tech Res Counc Turkey, Ankara, Turkey, 1999) Tanatar, Bilal
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.
Open Access
Hartree-Fock approximation of bipolaron state in quantum dots and wires
(Springer, 2010) Senger, R. T.; Kozal, B.; Chatterjee, A.; Erçelebi, A.
The bipolaronic ground state of two electrons in a spherical quantum dot or a quantum wire with parabolic boundaries is studied in the strong electron-phonon coupling regime. We introduce a variational wave function that can conveniently conform to represent alternative ground state configurations of the two electrons, namely, the bipolaronic bound state, the state of two individual polarons, and two nearby interacting polarons confined by the external potential. In the bipolaron state the electrons are found to be separated by a finite distance about a polaron size. We present the formation and stability criteria of bipolaronic phase in confined media. It is shown that the quantum dot confinement extends the domain of stability of the bipolaronic bound state of two electrons as compared to the bulk geometry, whereas the quantum wire geometry aggravates the formation of stable bipolarons.
Open Access
Lasing modes of infinite periodic chain of quantum wires
(IEEE, 2009-06-07) Byelobrov, V. O.; Benson, T. M.; Sewell, P.; Altıntaş, Ayhan; Nosich, A. I.
In this paper, we study the scattering and eigenvalue problems for a periodic open optical resonator that is an infinite chain of active circular cylindrical quantum wires standing in free space. The scattering problem is solved by the method of partial separation of variables. The eigenvalue problem differs from the first one by the absence of the incident field and presence of "active properties" of cylinders and yields the frequencies and thresholds of lasing. ©2009 IEEE.
Open Access
Nonradiative energy transfer in colloidal CdSe nanoplatelet films
(Royal Society of Chemistry, 2015) Güzeltürk, B.; Olutas M.; Delikanlı, S.; Keleştemur, Y.; Erdem, O.; Demir, Hilmi Volkan
Nonradiative energy transfer (NRET) has been extensively studied in colloidal nanocrystal (quantum dots) and nanorod (quantum wires) assemblies. In this work, we present the first account of spectroscopic evidence of NRET in solid thin films of CdSe based colloidal nanoplatelets (NPLs), also known as colloidal quantum wells. The NRET was investigated as a function of the concentration of two NPL populations with different vertical thicknesses via steady state and time resolved spectroscopy. NRET takes place from the NPLs with smaller vertical thickness (i.e., larger band gap) to the ones with a larger vertical thickness (i.e., smaller band gap) with efficiency up to ∼60%. Here, we reveal that the NRET efficiency is limited in these NPL solid film assemblies due to the self-stacking of NPLs within their own population causing an increased distance between the donor-acceptor pairs, which is significantly different to previously studied colloidal quantum dot based architectures for nonradiative energy transfer. © The Royal Society of Chemistry 2015.
Open Access
Phonon confinement and screening effects on the polaron energy in quantum wires
(Institute of Physics Publishing Ltd., 1995) Tanatar, Bilal; Guven, K.
We study the contribution of confined phonons to the polaron energy in quantum-well wires. We use a dispersionless, macroscopic continuum model to describe the phonon confinement in quantum wires of square cross section. The polaron energy is calculated variationally incorporating the dynamic screening effects. We find that the confined phonon contribution to the polaron energy is comparable to that of bulk phonons in the density range N = 104-107 cm-1. Screening effects within the random-phase approximation significantly reduce the electron-confined phonon interaction, whereas the correlation effects tend to oppose this trend.
Open Access
Raman scattering from confined phonons in GaAs/AlGaAs quantum wires
(Academic Press, 1998) Bairamov, B. H.; Aydınlı, Atilla; Tanatar, Bilal; Güven, K.; Gurevich, S.; Mel'tser, B. Ya.; Ivanov, S. V.; Kop'ev, P. S.; Smirnitskii, V. B.; Timofeev, F. N.
We report on photoluminescence and Raman scattering performed at low temperature (T = 10 K) on GaAs/Al 0.3Ga 0.7As quantum-well wires with effective wire widths of L = 100.0 and 10.9 nm prepared by molecular beam epitaxial growth followed by holographic patterning, reactive ion etching, and anodic thinning. We find evidence for the existence of longitudinal optical phonon modes confined to the GaAs quantum wire. The observed frequency at ω L10 = 285.6 cm -1 for L = 11.0 nm is in good agreement with that calculated on the basis of the dispersive dielectric continuum theory of Enderlein† as applied to the GaAs/Al 0.3Ga 0.7As system. Our results indicate the high crystalline quality of the quantum-well wires fabricated using these techniques. © 1998 Academic Press.
Open Access
Short-range correlations in coupled quantum-wire systems
(TÜBİTAK, 2002) Yurtsever, A.; Tanatar, Bilal
We study the contact values of the inter-wire pair-correlation function in electron-electron and electron-hole double-wire systems. For this purpose the ladder approximation as generalized to multicomponent systems is used. The ladder approximation yields positive values for the inter-wire gee(0) and geh(0) for all values of the density parameter rs and distance d between the wires. This allows us to infer possible instabilities in the system more reliably compared to other approaches. We also investigate the effects of quantum-wire width and screening on the inter-wire pair-correlation functions.
Open Access
Spin correlations in a quasi-one-dimensional electron gas
(Elsevier BV, 1996) Tanatar, Bilal
We study the spin correlations in a quasi-one-dimensional electron gas within the self-consistent-field approximation (SCFA). Electrons confined in a parabolic potential restricted to have free motion in one space dimension, and interact via a Coulomb-type potential are assumed to model quantum wires as realized in semiconductor structures. Density and spin-density response of the interacting electron system is investigated where correlation effects beyond the random-phase approximation (RPA) are embodied in the local-field factors. We calculate the spin-dependent pair-correlation functions and effective potentials, and determine the paramagnon dispersion. We find that electron correlation effects signal a paramagnetic instability for rs > 1.5.
Open Access
Strong coupling characterisation of quasi-1D polarons in cylindrical QW-wires
(Pergamon Press, 1996) Erçelebi, A.; Senger, R. T.
We retrieve, within the strong-coupling theory, the quasi-one dimensional analog of the standard optical polaron relevant to a cylindrical quantum well wire. Under the assumption of perfect confinement the ground state binding energy, effective polaronic mass and the phonon-coupling-induced potential well profiles are given as a function of the wire radius and the electron-phonon interaction strength.