Ellipsometric Study of Self-Assembled InAs/GaAs Quantum Dots

We measured the pseudo-dielectric function of self-assembled InAs/GaAs quantum dots at room temperature using spectroscopic ellipsometry. We observed a strong excitonic peak at 0.9 eV, which was attributed to quantum dot transitions. 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. Our room temperature data are very similar to the 1.8 K photoluminescence excitation spectra of InAs/GaAs quantum dots reported in the literature. The higher energy dielectric response of the quantum dots enabled us to estimate the morphology of the quantum dots using effective medium analysis. These results were compared to atomic force microscopy measurement results. Effective medium analysis showed that a GaAs cap layer was preferentially grown on the InAs wetting layer rather than on InAs islands.