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Optics and Spectroscopy

Investigation of the mechanisms of exciton coherence relaxation in single GaAs/AlGaAs quantum wells by the methods of excitonic induction

S. V. Poltavtsev, V. V. Ovsyankin, Boris V. Stroganov, Yu. K. Dolgikh, Sergei A. Eliseev, Yu. P. Efimov, V. V. Petrov

Published Oct 1, 2008• 4 citations
Publisher

Abstract

The mechanisms of exciton coherence relaxation in GaAs quantum wells in the linear mode have been experimentally investigated. An experimental technique has been developed for measuring the total phase relaxation rate, rates of reversible and temperature-irreversible excitonic phase relaxation, and the radiative decay rate Γ R of excitonic polarization. The experimental values of Γ R for a quantum well of specified thickness, obtained for a series of samples, have a spread not larger than 15%. This accuracy made it possible to estimate the shape of the dependence of Γ R on the well thickness L Z . It is experimentally found that Γ R is temperature-independent up to 80 K.

DOI
10.1134/s0030400x08100044

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The time evolution and kinetics of photoluminescence (PL) spectra of interwell excitons in double GaAs/AlGaAs quantum wells ( n-i-n structures) have been investigated under the pulse resonance excitation of intrawell 1sHH excitons using a pulsed tunable laser. It is found that the collective exciton phase arises with a time delay relative to the exciting pulse (several nanoseconds), which is due to density and temperature relaxation to the equilibrium values. The origination of the collective phase of interwell excitons is accompanied by a strong narrowing of the corresponding photoluminescence line (the line width is about 1.1 meV), a superlinear rise in its intensity, a long time in the change of the degree of circular polarization, a displacement of the PL spectrum toward lower energies (about 1.5 meV) in accordance with the filling of the lowest state with the exciton Bose condensate, and a significant increase in the radiative decay rate of the condensed phase. The collective exciton phase arises at temperatures T <6 K and interwell exciton densities n =3×10 10 cm −2 . Coherent properties of the collective phase of interwell excitons and experimental manifestations of this coherence are discussed.
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