Raman spectra of Si∕Ge∕Si (100) structures with Ge quantum dots (QDs) obtained by means of the low-temperature (200–300°C) molecular beam epitaxy are investigated. An extremely narrow Ge phonon line of the “anomalously” high intensity and a doublet structure of the Ge–Si mode are observed. These features are explained by the formation of a pure pseudomorphic state of a QD array to a Si substrate. Additional broad Ge phonon lines related to inelastic strain relaxation are found under the variation of growth conditions. The observed strain relaxation is strongly nonuniform for the two well known mechanisms of inelastic strain relaxation.

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Ge layer grown on Si(100) at the low temperature of ∼100 °C by molecular beam epitaxy is studied using scanning tunneling microscopy and Raman spectroscopy. It is found that crystalline and pseudomorphic to the Si substrate Ge islands are formed at the initial growth stage. The islands acquire the base size of 1.2–2.6 nm and they form arrays with the super-high density of (5–8) × 1012 cm−2 at 1–2 nm Ge coverages. Such a density is at least 10 times higher than that of Ge “hut” clusters grown via the Stranski-Krastanov growth mode. It is shown that areas between the crystalline Ge islands are filled with amorphous Ge, which is suggested to create potential barrier for holes localized within the islands. As a result, crystalline Ge quantum dots appear being isolated from each other.