Many‐Body Theory for the Dense Exciton Gas of Direct Semiconductors. III. Response of the Many‐Exciton System on an Externally Driven Light Field

The nonlinear response of a dense exciton gas in a platelet on an externally driven field is discussed using non equilibrium Green's function technique. A generalized Boltzmann‐equation of excitons containing many‐particle corrections in the diffusion‐, drift‐ and collision‐term is derived. Using a relaxed distribution (Boltzmann‐distribution) and an unrelaxed distribution (macro‐occupation) of ls‐excitons a bistability in exciton density as well as in the transmitted light intensity is obtained for a nearly resonant and stationary applied pump‐field of intensity 0.1 and 10kW/cm 2 , respectively. The bistability is obtained as a pure excitonic effect below the Mott‐transition.