Exciton diamagnetic shift in realistic quantum wells

Abstract

Exciton absorption spectra, diamagnetic shifts and localization of wave functions in realistic AlGaAs quantum wells with disorder are investigated. Two effective electron masses are chosen, bulk and enhanced due to confinement, in order to show the mass influence on the exciton properties. Whereas the absorption spectra and the localization of the wave function are modified only slightly, the diamagnetic shift turns out to be very sensitive. It is also shown that the average diamagnetic shift increases with the exciton energy.Semiconductor quantum wells (QW) have been a subject of intensive study for many years. The reduction in size of active layers in these structures leads to a stronger influence of imperfections, specifically well width fluctuations. Near band-edge optical properties of semiconductors are dominated by the excitons. Their sensitivity to disorder and especially the localization of the exciton wave function gives us the possibility to investigate certain aspects of the underlying structure at the length of the exciton Bohr radius (see Ref.[1] and references therein).Up to now, numerical simulations of the exciton properties were performed using either potentials generated artificially or coming from simple growth simulations [2]. Good agreement between theory and experiment could be achieved if two basic parameters of the disorder in the confinement potential (variance and correlation length) were adjusted (see e.g. [3]). Recently, the previously used factorization of the total wave function valid for weak disorder was tested and some differences in the absorption spectra and the wave function properties were revealed [4]. It has also been confirmed both theoretically [4] and experimentally [5], that the diamagnetic shift varies in a non-monotonic way among different localized excitons. Furthermore, the reduced values of the measured diamagnetic shift could not be explained only by the influence of the disorder. The giant magnetoresistance as a combined effect of both: the disorder and the magnetic field, has been observed in coupled QWs [6].In this paper, a potential correlation function deduced from experiment [7] is taken as input to generate new electron and hole lateral disorder potentials. The exciton Schrödinger equation is solved exactly including a perpendicular magnetic field. Absorption spectra and diamagnetic shifts are calculated. Two values for the electron effective mass are adopted: the bulk one (m . It is shown that the diamagnetic shift is very sensitive to the choice of the effective electron mass, unlike absorption spectra, binding energies, or localization of the wave function.The single sublevel approximation with the confinement wave functions for electron u e (z e ) and hole u h (z h ) of the realistic quantum well is assumed [7]. Then, the in-plane Hamiltonian for excitons in a disordered QW in effective mass approximation under applied perpendicular magnetic field B in the Coulomb

Optical exciton Aharonov-Bohm effect, persistent current, and magnetization in semiconductor nanorings of type I and II

“…The necessity of a high (deep) potential of the lighter particle has already been pointed out. 34 The material which matches these criteria best is InAs/AlGaSb in our case. This system clearly deserves further investigations, both theoretically and experimentally.…”

“…In the limiting case of strong electron and hole confinement which can be achieved either by combining materials with appropriate band alignments or by the inclusion of strain, 34 the wave function can be further factorized…”

Magnetoexcitonic optical absorption in semiconductors under strong magnetic fields and intense terahertz radiation in the Voigt configuration

“…On the other hand, it is also well known that a strong static magnetic field leads to not only the diamagnetic shift of the absorption edge but also a series of discrete peaks in the optical absorption spectra. These distinct peaks are due to the Landau quantization of the motion of electrons and holes in the plane perpendicular to the magnetic field [17][18][19]. Thus, the extension of the THz dynamical Franz-Keldysh effect to magnetoexcitons will be a very interesting subject.…”