Tn situ monitoring of InAs-on-GaAs quantum dot formation in MOVPE by reflectance-anisotropy-spectroscopy and ellipsometry

The formation of InAs quantum dots (QDs) on GaAs(001) during metalorganic vapour phase epitaxy (MOVPE) was studied for the first time in situ by reflectance-anisotropy-spectroscopy (RAS/RDS) and spectroscopic ellipsometry (SE). To analyze in detail the optical response of this highly lattice mismatched system, first RAS and SE spectra were taken for well defined InAs coverages (every 0.5 monolayers). During the initial wetting layer growth the surface dimer configuration changes from a c(4 x 4)/GaAs-like to a (2 x 4)InAs-like reconstruction. After the transition to 3-dimensional growth characteristic features in the RAS spectra indicate an anisotropic shape of the growing QDs. The transition from two dimensional to three dimensional growth was monitored in real time. Substrate temperatures and growth rates have been systematically changed and the postgrowth evolution of the self assembling islands was studied. By taking RAS and ellipsometry transients at characteristic photon energies and by comparing our experimental results to calculations based on an anisotropic effective medium model, we gained insight into the evolution of sample properties such as QD density and (averaged) QD size.