LUMINESCENCE SPECTROSCOPY OF INAS SELF-ASSEMBLED QUANTUM DOTS

We present selective photoluminescence and photoluminescence excitatio n spectroscopy on self-assembled quantum dots. These spectroscopic tec hniques reveal a large apparent 'Stokes' shift in In(Ga)As-Ga(Al)As se lf-assembled quantum dots. We demonstrate that the first two excited s tates observed in PLE originate from the doubly-degenerate first excit ed state. The ground state is not observed in the quantum dot PLE due to the sharp d-funtion-like density of states of individual dots. Our experimental data agree with a recent theoretical calculation, suggest ing that both the degeneracy-lifting and broadening of energy levels a re caused by the random potential of compositional, size and strain fl uctuations. Due to large energy separations in these quantum dots, we also demonstrate the importance of multi-phonon relaxation processes. (C) 1997 Academic Press Limited