TRANSMISSION ELECTRON-MICROSCOPY OBSERVATION OF THE EARLY GROWTH-STAGES OF SIGE GROWN ON SI SUBSTRATES BY CONVENTIONAL LOW-PRESSURE CVD

TEM was used to observe lattice defects in Si0.75Ge0.25 islands and in the film subsequently grown by conventional LPCVD at 680 degrees C on (100)-oriented and 0.5 degrees-misoriented Si substrates without any buffer layers. Large isolated islands grew on the oriented substrate. The lattice-mismatched islands, which contained the defects originated from the surface contaminants, released their strain energy by genera ting lattice-misfit dislocations and thus the thick film was relaxed. Reducing the growth temperature decreased the size of the islands, whi ch enabled a strained film to be grown. Many coalesced islands grew on the misoriented substrate at 680 degrees C. No misfit dislocations we re observed in the thick film. This was thought to be due to the incre ase in the nucleation sites depending on the step density of the subst rate surface. In contrast to the undoped alloy, the highly B-doped all oy grew coherently on the oriented substrate at 680 degrees C. The hig h B-doping seems to reduce lattice strain so that the alloy growth ini tiates in a two-dimensional growth mode.