Temperature dependence of the optical properties of high-density GaAs quantum dots

We investigate the effect of the quantum dot (QD) density on the thermal escape and the retrapping processes of carriers for unstrained GaAs/AlGaAs QDs through temperature-dependent photoluminescence measurements. We fabricated high-density GaAs QDs (8. 4 × 10 ¹⁰/cm ², dot-dot distance ~34 nm) on an Al _{0. 3}Ga _{0. 7}As/GaAs (111)A surface by using droplet epitaxy. The average lateral size and height of the GaAs QDs are 24 and 6 nm, respectively. Temperature-dependent photoluminescence (PL) studies show that high-density GaAs QDs undergo a sigmoidal-shape energy shift. The sigmoidal dependence of the PL peak energy can be explained by thermal escaping of carriers followed by re-trapping by QDs. Our analysis indicates that the re-trapping probability of thermally-escaped carriers increases with decreasing dot-to-dot distance (corresponding to an increase in the QD density).