Direct observation of carrier dynamics in the localization states of InGaN/GaN quantum wells

Light-emission devices based on InGaN/GaN quantum well (QW) bring about an ongoing revolution in general lighting. One of the highly deliberated discussions in this field is the steep efficiency drop with the increasing indium content of InGaN/GaN QW, posing a critical challenge to InGaN-based long-wavelength optoelectronic devices. Unfortunately, the factors that underlie the limitation remain unclear. Here, by using femtosecond transient absorption spectroscopy, we investigate the carrier dynamics of InGaN/GaN QW and find that the luminescence efficiency of InGaN/GaN QW is closely related to the localization states (LSs), i.e., dot-like In-rich InGaN clusters, in the InGaN layer. We demonstrate that the increase in the indium content can not only decrease the potential depth of LSs to weaken the localization binding effect and enhance the possibility of electrons being trapped by defects, but also enhance the density of LSs to increase the recombination channels and enlarge the full width at half maximum of the luminescence spectra. With these findings, we propose a model of carrier dynamics to deeply understand the emission mechanisms of InGaN/GaN QW, paving a way towards realizing high-performance InGaN-based optoelectronic devices.