Polariton Dispersion Law in Periodic Bragg and Near-Bragg Multiple Quantum Well Structures

The structure of polariton spectrum is analyzed for periodic multiple quantum well structures with periods at or close to Bragg resonance condition at the wavelength of the exciton resonance. The results obtained used to discuss recent reflection and luminescent experiments by M. H\"{u}bner et al [Phys. Rev. Lett. {\bf 83}, 2841 (1999)] carried out with long multiple quantum well structures. It is argued that the discussion of quantum well structures with large number of wells is more appropriate in terms of normal modes of infinite periodic structures rather then in terms of super- and sub- radiant modes.Comment: replaced with a new version, an error in one of the equations is correcte

Effects of inhomogeneous broadening on reflection spectra of Bragg multiple quantum well structures with a defect

The reflection spectrum of a multiple quantum well structure with an inserted defect well is considered. The defect is characterized by the exciton frequency different from that of the host's wells. It is shown that for relatively short structures, the defect produces significant modifications of the reflection spectrum, which can be useful for optoelectronic applications. Inhomogeneous broadening is shown to affect the spectrum in a non-trivial way, which cannot be described by the standard linear dispersion theory. A method of measuring parameters of both homogeneous and inhomogeneous broadenings of the defect well from a single CW reflection spectrum is suggested.Comment: 27 pages, 6 eps figures; RevTe