Ellipsometric study of self-assembled InAs/GaAs quantum dots

We measured the pseudo-dielectric function of self-assembled InAs/GaAs quan tum dots at room temperature using spectroscopic ellipsometry. We observed a strong excitonic peak at 0.9 eV, which was attributed to quantum dot tran sitions. We also observed a plateau from 1.2 eV to 1.4 eV, which arose from steplike joint density of states originating from an InAs wetting layer. O ur room temperature data are very similar to the 1.8 K photoluminescence ex citation spectra of InAs/GaAs quantum dots reported in the literature. The higher energy dielectric response of the quantum dots enabled us to estimat e the morphology of the quantum dots using effective medium analysis. These results were compared to atomic force microscopy measurement results. Effe ctive medium analysis showed that a GaAs cap layer was preferentially grown on the InAs wetting layer rather than on InAs islands.