Abstract | The interfacial properties of a series of Si/Si₁₋ₓGeₓ superlattices with the same unit period (∼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°C are studied by x-ray and Raman scattering techniques. For growth at 250°C, the interfaces are chemically abrupt, but exhibit a pronounced vertically correlated physical roughness that increases from ∼0.3 nm near the substrate to ∼2 nm at the surface. Growth at intermediate temperatures (400–550°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 (∼0.14° toward [001]) and with an inplane length scale of ∼1.2 µrn is observed. Higher growth temperatures (620–750°C) further enhanced the intermixing and caused undulation (100 nm length scale) of the interfaces. |
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