NATURE AND EVOLUTION OF INTERFACES IN SI/SI1-XGEX SUPERLATTICES

The interfacial properties of a series of Si1-xGex/Si superlattices with the same unit period (similar to 10 nm Si and 5 nm Si0.65Ge0.35) but with different number of repetitions (5, 10, 20) or prepared at different temperatures in the range 250-750 degrees C are studied by x-ray and Raman scattering techniques. For growth at 250 degrees C, the interfaces are chemically abrupt, but exhibit a pronounced vertically correlated physical roughness that increases from similar to 0.3 nm near the substrate to similar to 2 nm at the surface. Growth at intermediate temperatures (400-550 degrees C) resulted in structures with physically smooth interfaces, independent of the number of periods, but intermixed over at least two monolayers, and asymmetrically broadened with an alloy/Si interface width about twice (0.25 vs 0.5 nm) that of the Si/alloy interface. In that temperature range, a roughness component aligned with the substrate miscut angle (similar to 0.14 degrees toward [001]) and with an inplane length scale of similar to 1.2 mu m is observed. Higher growth temperatures (620-750 degrees C) further enhanced the intermixing and caused undulation (100 nm length scale) of the interfaces.