Structure, morphology and evolution of interfaces in Si/Si1-xGex superlattices

The interfaces in Si0.65Ge0.35/Si superlattices grown at different temperatures (250\u2013750 \ub0C) and number of repetitions (5, 10, 20) are studied by x-ray and Raman scattering techniques. At 250 \ub0C the interfaces are chemically abrupt, but exhibit a pronounced vertically correlated physical roughness that increases in magnitude with thickness. In the range of 400\u2013550 \ub0C interfaces are smooth but intermixed over at least two monolayers, and asymmetrically broadened with the alloy/Si interfaces width about twice (0.25 vs 0.5 nm) that of the Si/alloy interfaces. At higher temperatures (620\u2013750 \ub0C) undulations of 1 nm amplitude and 100 nm length scale develop at the alloy/Si interfaces. This morphological change appears to be strain-driven and causes some relaxation of the built-in strain. Moderate annealing (20 s at 750 \ub0C) induces partial relaxation of the superlattices and out-diffusion ( 3c0.5 nm) of Ge into the contiguous Si layers, but has relatively little effect on the interfacial widths.NRC publication: Ye