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. Known restriction on the condensation in low-dimensional systems can be lifted due to a disorder resulting from the chaotic potential.The manifestations of the finite exciton lifetime and, correspondingly, of the non-equilibrium nature of the excitonic system caused by the in- and out-scattering of excitons to the condensate state are analyzed. Other collective phases of excitons, namely, two-dimensional crystal of dipolar excitons and the electron-hole liquid, formed as a result of interparticle interactions, are discussed.