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Journal of Experimental and Theoretical Physics Letters

Superradiance of a degenerate exciton gas in semiconductors with indirect fundamental absorption edge

Vladimir S. Krivobok, С. Н. Николаев, Victor S. Bagaev, Владимир Сергеевич Лебедев, Е. Е. Онищенко

Published Nov 1, 2014• 2 citations
Publisher

Abstract

It is predicted that superradiant states can be formed in a degenerate exciton gas in a semiconductor with an indirect fundamental absorption edge. The superradiance results from four-particle recombination processes and occurs at photon energies approximately twice as high as the band gap energy. Experimental results supporting the possibility of the observation of superradiance from SiGe/Si quantum wells are presented.

DOI
10.1134/s0021364014170081

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It is predicted that superradiant states can be formed in a degenerate exciton gas in a semiconductor with an indirect fundamental absorption edge. The superradiance results from four-particle recombination processes and occurs at photon energies approximately twice as high as the band gap energy. Experimental results supporting the possibility of the observation of superradiance from SiGe/Si quantum wells are presented.
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The theoretically predicted rapid superradiant decay of coherent 2D excitons on a time scale of approximately 10 ps [1] is expected to be strongly enhanced in multiple QW (MQW) Bragg structures consisting of N identical QWs separated by (Ga,Al)As barriers the thickness of which was adjusted so that the QWs had a distance d equal to one half of the heavy-hole exciton resonance wavelength λ in the medium [2]. This enhancement originates from efficient radiative coupling of excitons excited in different wells via the exchange of transverse photons. Recently we have published [3] degenerate-four-wave-mixing experiments with fs optical pulses on GaAs QW Bragg structures which demonstrate that the radiative lifetime in high-quality GaAs single QWs (SQW) is approximately 5 ps and decreases to less than 2 ps in Bragg samples with N=10. These studies revealed that radiative recombination provides the dominant contribution to the homogenous linewidth of the 2D exciton in high-quality samples and exceeds nonradiative contributions caused by scattering with sample imperfections in contrast to previous assumptions.
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