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Abstract
If light beam propagates through matter containing point impurity centers, the amount of energy absorbed by the media is expected to be either independent of the impurity concentration N or proportional to N, corresponding to the intrinsic absorption or impurity absorption, respectively. Comparative studies of the resonant transmission of light in the vicinity of exciton resonances measured for 15 few-micron GaAs crystal slabs with different values of N, reveal a surprising tendency. While N spans almost five decimal orders of magnitude, the normalized spectrally-integrated absorption of light scales with the impurity concentration as N1/6. We show analytically that this dependence is a signature of the diffusive mechanism of propagation of exciton-polaritons in a semiconductor.
Highlights
Exciton-polaritons are light-matter quasiparticles which may be excited by light in the spectral vicinity of exciton resonances in semiconductors[1]
The samples for our studies were based on the epitaxial layers of GaAs, grown on the bulk semi-insulating GaAs substrates by means of either molecular beam epitaxy (MBE) or vapor phase epitaxy (VPE)
In what follows we show that in the diffusive propagation regime, the integrated absorption is governed by the characteristic time spent by diffusing polaritons in the crystal slab, which in turn depends non-linearly on the impurity concentration
Summary
Exciton-polaritons are light-matter quasiparticles which may be excited by light in the spectral vicinity of exciton resonances in semiconductors[1]. It is well known that the group velocity of an EP may vary from the speed of light in the semiconductor crystal down to the speed of a mechanical exciton which is several orders of magnitude lower, depending on the relative weight of excitonic and photonic fractions[10]. Due to their excitonic component, EPs efficiently interact with acoustic phonons, eventually decaying non-radiatively. Due to their photonic component, EPs can decay radiatively to vacuum photonic modes outside the sample[11]. The spectrally resolved absorption of light in a crystal A is related to the reflectivity R and transmission T by the energy conservation law:
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