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 metalorga nic vapour phase epitaxy (MOVPE) was studied for the first time in sit u by reflectance-anisotropy-spectroscopy (RAS/RDS) and spectroscopic e llipsometry (SE). To analyze in detail the optical response of this hi ghly lattice mismatched system, first RAS and SE spectra were taken fo r well defined InAs coverages (every 0.5 monolayers). During the initi al 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 tr ansition to 3-dimensional growth characteristic features in the RAS sp ectra indicate an anisotropic shape of the growing QDs. The transition from two dimensional to three dimensional growth was monitored in rea l time. Substrate temperatures and growth rates have been systematical ly changed and the postgrowth evolution of the self assembling islands was studied. By taking RAS and ellipsometry transients at characteris tic photon energies and by comparing our experimental results to calcu lations based on an anisotropic effective medium model, we gained insi ght into the evolution of sample properties such as QD density and (av eraged) QD size.