Spectral diffusion in nitride quantum dots: Emission energy dependent linewidths broadening via giant built‐in dipole moments

We present a study about the origin of the huge emission linewidths broadening commonly observed for wurtzite GaN/AlN quantum dots. Our analysis is based on a statistically significant number of quantum dot spectra measured by an automatized µ‐photoluminescence mapping system applying image recognition techniques. A clear decrease of the single quantum dot emission linewidths is observed with rising overall exciton emission energy. 8‐band k · p based model calculations predict a corresponding decrease of the built‐in exciton dipole moments with increasing emission energy in agreement with the measured behavior for the emission linewidths. Based on this proportionality we explain the particular susceptibility of nitride quantum dots to spectral diffusion causing the linewidth broadening via the linear quantum‐confined Stark effect. This is the first statistical analysis of emission linewidths that identifies the giant excitonic dipole moments as their origin and estimates the native defect‐induced electric field strength to ～2 MV/m. Our observation is in contrast to less‐polar quantum dot systems as e.g. arsenides that exhibit a naturally lower vulnerability to emission linewidth broadening due to almost negligible exciton dipole moments. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)