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or weak binding
t, or weak binding, excitons [3], as opposed to tightly bound Frenkel excitons [4]. Apart from a small reduced mass, the electron–hole attraction is screened by the large dielectric constant ε ≈ 10 and the exciton binding energy Eb, i.e., the difference between the 1S exciton line and the electronic band structure gap, is only a tiny fraction of the Rydberg, not more than a few tens of meV. The envelope function approach is well suited to describe Wannier–Mott excitons, as discussed in Section 2 for the bulk and in Section 3 for quantum confined structures [5],authentic jordan for sale. In the most relevant case of a quantum well thickness L of the order of the Bohr radius, the motion of the electron and of the hole along the growth 97 THIN FILMS AND NANOSTRUCTURES, Vol,jordanscategories.com. 31 Copyright . 2003 by Elsevier Inc. ISSN 1079-4050 All rights reserved DOI 10.1016/S1079-4050(03)31002-6 G.C. LA ROCCA direction are separately quantized and the binding energy and oscillator strength of the quantum well exciton are significantly increased compared to the bulk. At high excitation density, non-linear effects come into play and the picture of excitons as ideal bosons is to be abandoned [6]. In Section 4, the most simple and basic considerations are discussed in the complex and still rapidly developing field of many-body and correlation effects in semiconductor optics [7]. In the intermediate density regime where the excitonic resonances still persist, the nonlinearities scale as n/nS where n is the two-dimensional exciton density and nS the corresponding saturation density nS ≈ 1/(πa2 2D),being a2D the two-dimensional exciton radius. Moreover, for appropriate conditions,wholsale authentic jordans, biexcitons,real air jordans, i.e., molecular states of two excitons bound together, may form and affect the optical properties [8]. Finally, the possibility of Bose–Einstein condensation of excitons will be considered [9]. 2. Wannier–Mott Excitons in Bulk Semiconductors 2.1,www.lovejumpman.com. BAND STRUCTURE OF DIRECT GAP SEMICONDUCTORS The electronic states of inorganic semic
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