OPTICAL-TRANSITIONS AND CARRIER RELAXATION IN SELF-ASSEMBLED INAS GAAS QUANTUM DOTS/

We present experimental results concerning optical transitions and car rier dynamics (capture and relaxation) in self assembled InAs/GaAs qua ntum dot structures grown by metalorganic vapor phase epitaxy. Photolu minescence (PL) measurements at high excitation level reveal optical t ransitions above the ground state emission. These transitions are foun d to originate from occupied hole states by solving the quantum dot ei genvalue problem. Time-resolved studies after non-resonant pulse excit ation exhibit a relaxation ladder of the excited carriers from the GaA s barrier down to the ground state of the quantum dots. From both the continuous-wave measurements and the PL-decay curves we conclude that the carrier relaxation at non-resonant excitation is mediated by Coulo mb interaction (Auger effect). PL-decay curves after resonant pulse ex citation reveal a longer rise time compared to non-resonant excitation which is a clear indication of a relaxation bottleneck inside the qua ntum dots. We interpret the rise time (approximate to 400 ps) in this case to originate from relaxation via scattering by acoustic phonons. The PL-decay time of the ground state emission approximate to 700 ps i s interpreted as the excitonic lifetime of the quantum dot. (C) 1996 A merican Institute of Physics.