R.A. Suris Ioffe Institute, ul. Polytekhnicheskaya 26, St. Petersburg, 194021, Russian Federation
A review of many-body effects in exciton ensembles in semiconductors is given with the emphasis on two-dimensional systems: structures with single and double quantum wells and with quantum microcavities. The Bose—Einstein condensation effect, an accumulation of a macroscopic number of excitons in the ground state of the system, is discussed. The known prohibition on condensation in low-dimensional systems can be lifted due to the disorder resulting from the chaotic potential. Manifestations of the finite exciton lifetime and, correspondingly, of the nonequilibrium of the excitonic system caused by processes of excitons entering and leaving the condensate state are analyzed. Other collective phases of excitons, namely, two-dimensional crystals of dipolar excitons and an electron-hole liquid, formed as a result of interparticle interactions, are discussed.