The role of interdiffusion and spatial confinement in the formation of resonant raman spectra of Ge/Si(100) heterostructures with quantum-dot arrays |
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Authors: | I V Kucherenko V S Vinogradov N N Mel’nik L V Arapkina V A Chapnin K V Chizh V A Yur’ev |
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Institution: | (1) Lebedev Physical Institute, Russian Academy of Sciences, Leninskiĭ pr. 53, Moscow, 119991, Russia;(2) Prokhorov General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991, Russia |
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Abstract: | The phonon modes of self-assembled Ge/Si quantum dots grown by molecular-beam epitaxy in an apparatus integrated with a chamber of the scanning tunneling microscope into a single high-vacuum system are investigated using Raman spectroscopy. It is revealed that the Ge-Ge and Si-Ge vibrational modes are considerably enhanced upon excitation of excitons between the valence band Λ3 and the conduction band Λ1 (the E 1 and E 1 + Δ1 transitions). This makes it possible to observe the Raman spectrum of very small amounts of germanium, such as one layer of quantum dots with a germanium layer thickness of ≈10 Å. The enhancement of these modes suggests a strong electron-phonon interaction of the vibrational modes with the E 1 and E 1 + Δ1 excitons in the quantum dot. It is demonstrated that the frequency of the Ge-Ge mode decreases by 10 cm?1 with a decrease in the thickness of the Ge layer from 10 to 6 Å due to the spatial-confinement effect. The optimum thickness of the Ge layer for which the size dispersion of quantum dots is minimum is determined. |
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