STRAIN RELIEF PROCESS AT HIGHLY STRAINED SEMICONDUCTOR HETEROINTERFACES STUDIED BY HIGH-RESOLUTION X-RAY-DIFFRACTION

We investigated the growth (molecular beam epitaxy) and the structural properties of ultrathin Si layers embedded in GaAs(100). Surface reconstructions were monitored by high-energy electron diffraction (RHEED) during growth. A (1 x 2) reconstruction was observed after about 0.05 nm Si growth, while a (2 x 2) reconstruction appeared after 0.4 nm. After exceeding the critical thickness a rotation of the GaAs lattice on Si with respect to the GaAs lattice of the substrate was observed. We show that the thickness of the Si layers can be determined with high accuracy by double-crystal X-ray diffraction. A dynamical model was used for the interpretation of the experimental X-ray diffraction data. The diffraction experiments indicate that the critical thickness of Si on GaAs is between 1.0 and 1.5 nm.