Quantum indistinguishability effects of confined polyexcitons

We report experimental evidence for the existence of confined polyexcitons in strain-relaxed epitaxial SiGe layers by means of low-temperature photoluminescence. The number of excitons, n, up to four in a polyexciton is confirmed. Our data clearly show that only one type of polyexciton is confined in potential wells generated by lower band-gap regions in SiGe layers due to alloy fluctuations. The radiative annihilation of a polyexciton with a given n produces n-1 photons and a single exciton left behind. The most striking fact is that confined polyexcitons having n>2 do not decay to polyexcitons having n-1. These observations can be explained by the quantum effect of indistinguishability of polyexcitons which possess either zero or integral spin. This effect is enhanced in a confined well since confined polyexcitons interact strongly among themselves in a limited spatial region. Our observations are important to understand the unique properties of a few quantum particles in a confined region. © 1999 The American Physical Society.