Dual localization in InGaN/GaN MQWs: Unveiling the bi-exponential decay in time-resolved photoluminescence

The bi-exponential decay characteristics are widely observed and correlated with localized nature of carrier dynamics in InGaN/GaN multiple quantum wells (MQWs). However, few studies focus on the physical origin of bi-exponential decay processes. A thorough understanding of the physical mechanism of the abnormal dual localization is still lacking. Here, a systematic optical spectroscopy investigation on MQWs and single quantum well is conducted. Two distinct types of carrier localization in MQWs have been identified from various perspectives. One is due to the fluctuation of the indium content, which makes the carriers localized at different energy potential minima, resulting in a diverse distribution of the emission wavelength in real space. In addition, the recombination rate decreases with the increase of the measurement wavelength. The other is due to the inhomogeneity of the electric field between each quantum well, wherein the electrons and holes are separately localized, resulting in a decreasing recombination rate with the increase of electric field. These two kinds of localization affect the carrier recombination simultaneously; as a result the decay curve in time resolved photoluminescence exhibits a bi-exponential characteristic at any measured wavelength. A clear understanding of localization is beneficial to precisely controlling the carrier dynamics in MQWs and improving the performances of optoelectronic devices.