Ultrafast carrier-relaxation dynamics in self-assembled InAs/GaAs quantum dots

We apply the recently developed technique of ultrafast scanning tunneling microscopy to study carrier dynamics in InAs/GaAs self-assembled quantum-dot samples. The results obtained with this new technique are compared with standard ensemble-averaging ultrafast optoelectronic techniques such as femtosecond optical pump/probe reflectivity measurements and time-resolved terahertz spectroscopy. These measurements reveal a unified picture of the relaxation dynamics in InAs/GaAs self-assembled quantum-dot samples at T = 300 K. The initial carrier relaxation proceeds by Auger carrier capture from the InAs wetting layer on a time scale of 1-2 ps, followed by recombination of carriers in the wetting layer, GaAs substrate, and quantum dots on time scales of 350 ps, 2.3 ns, and 900 ps, respectively. The consistency of these three experimental techniques demonstrates ultrafast scanning tunneling microscopy as a reliable tool for probing the local dynamics of nanostructures.