Free carrier, free, and bound exciton photoluminescence of quantum well

Free exciton and bound exciton photoluminescence (PL) of a quantum well (QW) in the presence of free carriers is studied in a model that includes the transfer of particles among free carrier, free exciton, and bound exciton states under an external excitation. It is shown that the free carrier state is important not only at high temperature but also at low temperature. General formulas for the free exciton, bound exciton, and free carrier PL are developed. The two-dimensional (2D) law of mass action for the free carrier and free exciton PL is reproduced at high temperature, and the model of the free exciton trapped by the impurities is obtained for the QW system with low defect concentration. Free exciton and bound exciton PL for high defect concentration is also discussed and the 2D law of mass action is obtained at high temperature as well. Experimental observations such as the thermal behavior of free exciton and bound exciton PL, the recently observed sharp temperature-induced reduction of the PL linewidth in coupled QW subjected to an electric field are discussed. An experiment is proposed to understand the origin of this sharp reduction.