An efficiency droop model of the saturated radiative recombination rate and its verification by radiative and nonradiative carrier lifetime measurements in InGaN-based light emitting diodes

Abstract

We have proposed an efficiency droop model which can comprehensively explain experimental IQE droop phenomena occurring at different temperatures, materials, and active structures. In our model, carriers are located and recombined both radiatively and nonradiatively inside randomly distributed In-rich areas of InGaN-based QWs and the IQE droop originates from the saturated radiative recombination rate and the monotonically increasing nonradiative recombination rate there. Due to small effective active volume and small density of states of In-rich areas, carrier density is rapidly increased even at low current density and the radiative recombination rate is easily saturated by different distributions of electrons and holes in the momentum k-space. A measurement method that can separately estimate the radiative and nonradiative carrier lifetimes just at room temperature is theoretically developed by analyzing the time-resolved photoluminescence (TRPL) response. The method is applied to a blue InGaN/GaN QW LED. The experimental results show that the radiative carrier lifetime increases and the nonradiative carrier lifetime saturates with increasing TRPL laser power, which is one of direct evidences validating our IQE droop model.