Recent experiments with Bose-condensate of indirect excitons in quantum-well traps in semiconductor heterostructures show long-scale coherence of recombination emission under appropriate CW laser pumping. We suggest that such coherence results from the existence of high-quality polariton modes, which are formed due to strong coupling of exciton polarization and electromagnetic field in a trap. These modes are of whispering-gallery origin and can be excited via stimulated emission of excitons supplied by the CW laser pumping. We analyze in detail the structure and spectrum of polariton modes taking into account polarization relaxation and radiative losses. We derive characteristic equation for mode wave-vectors and solve it numerically for the experimental parameters. The quality factors of a small number of modes are found to reach 10000 and higher. In the case of high density and narrow enough spectral linewidth of excitons, which could be achieved due to Bose-Einstein condensation, some modes become unstable giving rise to exciton lasing. We investigate their growth rates, instability thresholds, energy losses, and saturation amplitudes. Under typical experimental conditions, we indicate lasing polariton modes which can be responsible for the observed long-scale coherence of exciton emission.

Date Published: 18 November 2008
PDF: 6 pages
Proc. SPIE 7138, Photonics, Devices, and Systems IV, 713826 (18 November 2008); doi: 10.1117/12.818077

Published in SPIE Proceedings Vol. 7138:
Photonics, Devices, and Systems IV
Pavel Tománek; Dagmar Senderáková; Miroslav Hrabovský, Editor(s)