UHV-CVD HETEROEPITAXIAL GROWTH OF SI1-XGEX ALLOYS ON SI(100) USING SILANE AND GERMANE

In this paper, we investigate the growth rate and strain relaxation of Si1-xGex layers grown on Si substrates by UHV-CVD. The Si1-xGex growt h rate is found to exhibit two different behaviors as a function of gr owth temperature. Above the temperature corresponding to hydrogen deso rption (T-H), the SiGe growth rate first decreases with x, and finally becomes almost independent of x at higher values of x. Below T-H, the SiGe growth rate first increases with x, then shows a maximum and fin ally becomes almost independent of x at higher values of x. Using in-s itu reflection high-energy electron diffraction (RHEED), transmission electron microscopy and photoluminescence, we have clearly identified two distinct mechanisms for strain relaxation as a function of Ge cont ent: at x=0.15 strain is relaxed by nucleation of misfit dislocations while the film surface remains smooth throughout growth and relaxation process. The introduction of dislocations is found to occur before la ttice relaxation. At x=0.22, strain is first relaxed via formation of coherent islands before reaching the equilibrium critical thickness fo r dislocation nucleation. We also show that in-situ RHEED is a powerfu l technique to probe the evolution of film morphology in an ultra high vacuum chemical vapour deposition system. (C) 1997 Elsevier Science S .A.