Carrier diffusion in InAs/GaAs quantum dot layers and its impact on light emission from etched microstructures

We have studied carrier diffusion in self-assembled InAs/GaAs quantum dots (QDs) and light emission from deeply etched microstructures containing QDs using a novel micro-photoluminescence technique based on scanning the laser excitation spot across an etched feature. Complete suppression of carrier diffusion is observed in these QDs at temperatures less than 150 K. At temperatures above 150 K the carrier diffusion length in the QD layer increases with increasing temperature but remains less than the carrier diffusion length in an InGaAs/GaAs quantum well (QW). Carrier diffusion lengths of 6.5 and 9.5 µm were measured for the QD and QW layers at room temperature, respectively. Photoluminescence spectra measured on the same QD sample over the 77–297 K temperature range indicate carrier redistribution occurring between different sized dots in the layer at temperatures above 70 K, suggesting carrier trapping in only the larger dots in the layer is sufficient to prevent carrier diffusion. The expected increase in non-radiative edge recombination in deeply etched microstructures with increasing carrier diffusion length is observed for etched photonic bandgap structures containing both QD and QW active layers. Despite the reduced carrier diffusion length in QD active layers, edge effects dominate carrier recombination processes in a 3.2 µm diameter etched microstructure containing InAs/GaAs QDs at room temperature.