ROLE OF THE WETTING LAYER IN THE CARRIER RELAXATION IN QUANTUM DOTS

We present picosecond time resolved photoluminescence measurements of GaAs/AlGaAs quantum dot structures-grown by modified droplet epitaxy-where no wetting layer is connecting the dots. We find a fast carrier relaxation time (30 ps) to the dot ground state, which becomes even faster for increasing the photogenerated carrier injection. This shows that the two-dimensional character of the wetting layer is not relevant in determining the quantum dot capture, in contrast with the conclusions of several models so far presented in literature. We discuss the role of the barrier states as well as the possibility of Auger processes involving the zero-dimensional levels of the quantum dots.