Abstract
We observed experimentally the strong effect of nonequilibrium phonons on the intensity of the luminescence of free and bound excitons, created by optical illumination of a Si surface immersed in liquid helium ( T = 1.8 K). The polarity of the phonon-induced luminescence signal strongly depends on the perfection of the surface. Two factors were included in the theoretical explanation of this effect: (1) the phonon-induced dissociation of bound excitons, and (2) the drag of free excitons by phonon flux (phonon-wind effect) which shifts the exciton cloud to the surface, where exciton recombination is strong. This effect is used to study spectral features of phonon propagation in Si and a-Si:H films.
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