Optically induced intraband electron transfer in self‐assembled InAs quantum dots

Abstract

In our experiments we superimpose a near-infrared excitation laser field with a mid infrared field on an InAs quantum dot ensemble or on a single quantum dot. In the latter case a cw infrared laser excitation and a glow-bar mid infrared field are superimposed in a confocal micro-photoluminescence configuration on a single quantum dot. By comparing the recombination spectra for the superimposed spectra with the spectra from the laser excitation we detect changes in the count rates for the different excitonic states. The decrease of the luminescence intensity in the lower states together with an increasing intensity in higher excited states suggests a direct electron transfer between these states due to absorption of mid infrared light. For the quantum dot ensembles we use interband pump – intraband probe-time domain spectroscopy to study the electron capture and relaxation dynamics within the ensemble. By tuning the femtosecond infrared pulses into resonance with transitions between confined quantum dot states and the wetting layer continuum we gain knowledge about the electron population in the quantum dots ground state and first excited states as a function of delay time between pump and probe pulse. Our experiments indicate the stepwise relaxation through the excited dot states to be the most efficient relaxation pathway into the dot ground state on a timescale between 1.5 ps and 4.7 ps depending on temperature and excitation density. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)