SELF-ASSEMBLED INAS GAAS QUANTUM DOTS UNDER RESONANT EXCITATION/

The energy structure and the carrier relaxation in self-assembled InAs /GaAs quantum dots (SADs) is investigated by photoluminescence excitat ion spectroscopy (PLE) and photoluminescence (PL) at resonant excitati on (below the GaAs and the wetting layer bandgap). In PLE measurements we find a clear resonance from the first excited hole state as well a s resonances from a relaxation via different phonons. From a compariso n of the PL-rise times in time resolved spectroscopy, we conclude on a fast electron relaxation (less than or equal to 50 ps) and a slow hol e relaxation with a time constant of about 400 ps. Different relaxatio n paths are observed in the InAs/GaAs quantum dot system and allow us to identify the hole relaxation in the SADs as multiphonon assisted tu nneling. The PL-decay time in the SADs after resonant excitation (abou t 600 ps) is attributed to the lifetime of the quantum dot exciton. In agreement with theoretical predictions, we find a constant lifetime o f about 600 ps for temperatures below 50 K and a linear increase of th e lifetime between 50 and 100 K with a slope of 26 ps/K. (C) 1998 Amer ican Institute of Physics. [S0021-8979(98)01903-3].