Manfred Bayer¹, Pawel Hawrylak², Simon Fafard² and Alfred Forchel¹

We present the results of a detailed study of excitons in In(Ga)As self-assembled quantum dots. Typically the magnitude of Coulomb interaction effects is smaller than the inhomogeneous broadening of spectra recorded on quantum dot arrays. For their resolution, optical spectroscopy on single quantum dots was performed.

For studying the exciton density of states, different types of dot structures were fabricated. Type 1 dots have only two confined electronic shells (s and p), while in type 2 dots an additional the d-shell is confined. From excitation spectroscopy we find that the exciton absorption depends strongly on the symmetry of the studied quantum dots. For dots, which exhibit rotational symmetry around the heterostructure growth direction, the spectra become particularly simple. For such structures, we observe a strong variation of the absorption spectra with the number of shells in the dots.

The variations of the dot symmetry are also reflected by the fine structure of the ground state exciton. The fine structure is determined by the electron-hole exchange interaction and by the Zeeman-interaction of the carrier spins with an external magnetic field. The symmetry class of the dots can be traced from the magnetic field dependences of the polarization of the emission and of the spin splitting.