Browsing by Subject "Semiconductors--Surfaces."

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    ItemOpen Access
    Phonon renormalization effects in low dimensional electron-hole systems
    (1995) Güven, Kaan
    Ia)vv (linuMisioiial sciniromluclor st i iid iii4's lia\4‘ 1и‘(М1 an (‘Xt(Misiv(‘ i4\soa,rrh iwcix ill (4)iul(4iscd iiiatlcr physics. In j^aii iculai', iiindi (‘llorl has 1)(Ч'п dcvolnd to lhc‘ study ol ciuasi-one-diiiK'iisional siMniconductor sli-iiclures in гесчмП, yc'ars. The IK'W physic'al pluMioiiK'iia. in\'ol\4*d in tlu'sc* sysitMUs arisin,^ diu‘ to th(‘ Г(‘(1п(чм1 dimensionality point to various |)ot(Milial applicalions for iuture teclinologi(.‘s. y\ltliough the theory is lainiliar with tin* "oiK'-dimensionar’ pi’oblem for a long time, the realization of such structures (also known as (juanlum wires) extends onl}^ to ¿1 decade belonx Ilowciver, the по\ч'1 рго(1 исГкя1 t(‘chni([n('s led to a rapid increase in the experimental studies which, in turn, required a mor(' realistic and comi)rc*hensive theory to anal^'/c' and int('rpr('t tln^ obtaiiKnl data. This tlu'sis work intends to make a contribution in i1k‘ diiH’ctioii of th(‘S(' imj>rovem(‘nts. Our study is based on a (juasi-one-diiiKMisional eh'ctron-hole syst em as realized in pliotoexcit(‘d quantum wires, interacting with tlu' bulk bO-])honons. VVe investigate the polaronic corrections to the band gap and the c:arri(n* eilective mass, cirid the dependence of this correction itself to carrier density, temperature, and quantum finite size effects. VVe apply two different formal approaches; tho' p(n·Lurl.)гıtion theory and the vaiiational iiK'thod. 'I'he latter enables the investigation of dynamical screening elfects, thereby clarifying tin? (luestion of validity of the static screi'iiing approximation in one dimension. Our results have shown that dynamical screening is r<'levant in low dimensions. The dielectric function, which is a key quantity in describing tin' many-particle properties, is analyzf'd under diihn(*nt tip'proximations such as the 1 lartree-Fock ap[)roximation, random-|)hase api)roximation. and the more advaiuaxl local-field correction. Several confinement |)otentials (inlinit(‘ well, paralrolic, cj lindrical) are presented. I'kxplicit results iirc.' ol)tained hn' a (¡a.As (|uan(iim wiiv. VVe compare the results of tin' |)olar(niic corn'cticnis with tluit of tin? (‘xchangecorndalion induced corrections. W'e loiiinl that they are comi)arable in orrler of magnitudi', indicating that cari'i('r-|)lu)non int('iactions are more enhanced as the dimensionality reduces, and Ik.micc' should be treated on tin etpial footing along with the carrier-carri(‘r interact i(jiis. WV* make comparison with the pohironic corrections in two diiiK'iisiinial sysUnus. kdiially, we brielly discuss the renormalization due to confined phuiions as well.
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    ItemOpen Access
    A theoretical model for the epitaxial growth of Si(100) surface
    (2000) Dağ, Sefa
    In this thesis, we investigated atomic scale mechanisms of growth on the Si(lOO) surface. First principles quantum molecular dynamics calculations are performed, where self-consistent field electronic structure calculations within the density functional theory, and ionic relaxations carried out concomitantly. By using this method, we first determined the binding energy and binding sites of adatoms and ad-dimers. In the second stage, we simulated different configuration of dimer construction. In the third stage, we analyzed temperature dependent behaviour of dimers and we investigated translational and rotational motion of dimers. Finally, we presented a new theoretical model for ID epitaxial growth.