Boson characteristics of the exciton–biexciton system in a GaAs/AlAs type-II superlattice

We report on the appearance of Bose–Einstein statistics of the exciton–biexciton system in a (GaAs)12/(AlAs)12 type-II superlattice. The density relation of the exciton and biexciton is estimated from time-resolved photoluminescence spectra at various excitation powers and bath temperatures. The long lifetime of the type-II exciton, e.g., 2 μs at 5 K, enables us to obtain the precise information of the density relation. In a relatively low exciton-density region, the biexciton density obeys a well-known square law. At an exciton density around 1×1010 cm−2, the biexciton density suddenly increases with a threshold-like nature. This behavior, which is realized at temperatures up to 8 K, can be understood from Bose–Einstein statistics.