The Role of Interdiffusion and Spatial Confinement in the Formation of Resonant Raman Spectra of Ge/Si(100) Heterostructures with Quantum-Dot Arrays

摘要

The phonon modes of self-assembled Ge/Si quantum dots grown by molecular-beamepitaxy in an apparatus integrated with a chamber of the scanning tunnelingmicroscope into a single high-vacuum system are investigated using Ramanspectroscopy. It is revealed that the Ge-Ge and Si-Ge vibrational modes areconsiderably enhanced upon excitation of excitons between the valence band$\Lambda_3$ and the conduction band $\Lambda_1$ (the E1 and E1 + $\Delta_1$transitions). This makes it possible to observe the Raman spectrum of verysmall amounts of germanium, such as one layer of quantum dots with a germaniumlayer thickness of 10 \r{A}. The enhancement of these modes suggests a strongelectron-phonon interaction of the vibrational modes with the E1 and E1 +$\Delta_1$ excitons in the quantum dot. It is demonstrated that the frequencyof the Ge-Ge mode decreases by 10 cm^-1 with a decrease in the thickness of theGe layer from 10 to 6 \r{A} due to the spatial-confinement effect. The optimumthickness of the Ge layer, for which the size dispersion of quantum dots isminimum, is determined.