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Conference on Lasers and Electro-Optics

Life-time limited dephasing time of confined exciton on CuCl quantum dots

Kuon Inoue, Ryosuke Kuribayashi, Kazuaki Sakoda, Alexander V. Baranov

Published Jan 1, 1998• 0 citations
Publisher

Abstract

Summary form only given. The dephasing time T/sub 2/ of an exciton in the weak confinement regime in semiconductor quantum dots (QDs) is expected to be quite long, or equivalently, the electronic structure should be composed of discrete ultranarrow or atomic-like levels. These characteristics are very attractive for potential application of QDs to devices. In view of no observation of such a long T/sub 2/ value, we directly measured T/sub 2/ of confined excitons in CuCl QDs by using both a degenerate fourwave-mixing (FWM) and a heterodyne photon echo (HPE) experiment, using very weak pumping power.

DOI
10.1109/cleo.1998.676147

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Ultranarrow homogeneous linewidth of a Z3{Z}_{3}Z3​ exciton in CuCl quantum dots was studied by using accumulated photon echo. CuCl quantum dots embedded in two kinds of matrices, namely, an alminoborosilicate glass and a NaCl crystal, were studied. The narrowest homogeneous linewidth at low temperature was 1 $\ensuremath{\mu}\mathrm{eV}.$ The temperature dependence of the homogeneous linewidth was similar, above 5 K for both kinds of samples, but in the lower-temperature region, a remarkable difference was observed between them. It indicates that the matrix definitely affects the dephasing process of a confined exciton in quantum dots at low temperatures. The observed temperature dependence was explained by the contribution of the confined phonon in quantum dots and the two-level system in the matrix.
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We use the Dresden Free-Electron-Laser (FELBE) to investigate intersublevel coherence times in semiconductor quantum dots (QDs) by degenerate four-wave mixing (DFWM) spectroscopy. We know from pump-probe measurements1on a series of quantum dot samples with varying intersublevel energy that intersublevel relaxation times of the s-p intersublevel transition can become very long (up to 1.5 ns). Due to the discrete nature of these sublevels, intersublevel coherence times should exhibit similar time constants at low temperatures where “pure dephasing” is suppressed.