Analysis of strain relaxation by microcracks in epitaxial GaAs grown on Ge/Si substrates

A detailed spectroscopic and morphological study of GaAs epitaxial layers grown by molecular beam epitaxy on Ge buffer layers deposited by low energy plasma enhanced chemical vapor deposition on Si is presented. The aim is to understand the nature of thermal strain relaxation induced by crack formation in the epilayers. The comparison of the experimental data on the spatial strain relaxation pattern with the theoretical prediction from a purely elastic model indicates that strain relaxation around cracks arises from two contributions. At short distances the main contribution is essentially plastic, due to the presence of extended defects. At large distances, on the contrary, elastic relaxation seems to dominate. It is also shown that GaAs grown on Ge/Si substrates is in a state of metastable strain as a consequence of the fact that cracks relax the thermal tensile strain only locally