Capture and Escape of Charge Carriers in Quantum Dots

A report describes an experimental investigation of effects of thermally induced intermixing of In0.6Ga0.4As and GaAs on the dynamics of photoexcited charge carriers in In0.6Ga0.4As/GaAs quantum dots. The quantum dots (nanometer-size islands of In0.6Ga0.4As surrounded by GaAs) were grown by metal-organic chemical-vapor deposition. The dynamics at temperatures from 60 to 300 K were investigated by time-resolved photoluminescence measurements with subpicosecond temporal resolution, on both specimens as grown and specimens in which intermixing had been effected by a post-growth anneal. The measurement data were interpreted as signifying that at lower temperatures, the carrier lifetimes in the dots are determined by radiative recombination, which becomes substantially faster after intermixing, while at temperatures >150 K, thermal emission of carriers predominates. Capture of carriers into the dots was found to be fast and governed by carrier-carrier scattering; at room temperature and high excitation intensity, a carrier capture time of 0.72 ps was observed in the intermixed dots. These findings have implications for the development of quantum-dot lasers.