Effect of interdiffusion and quantum confinement on Raman spectra of the Ge/Si(100) heterostructures with quantum dots

TL;DR

This study investigates how interdiffusion and quantum confinement affect the Raman spectra of Ge/Si quantum dots, revealing enhanced vibrational modes and size-dependent phonon frequency shifts using Raman scattering.

Contribution

It demonstrates the influence of interdiffusion and quantum confinement on Raman spectra of Ge/Si quantum dots, including phonon frequency shifts and the ability to detect signals from very small volumes.

Findings

Enhanced Ge-Ge and Si-Ge vibrational modes at specific excitations

Si diffusion into Ge quantum dots forming Ge_xSi_{1-x} solid solution

Decrease in Ge-Ge mode frequency with reduced layer thickness

Abstract

We used Raman scattering for study the phonon modes of self-organized Ge/Si quantum dots, grown by a molecular-beam epitaxy method. It is revealed, that Ge-Ge and Si-Ge vibrational modes considerably intensify at excitation of exciton between the {Lambda}3 valence and {Lanbda}1 conduction bands (transitions E1 and E1+{Delta}1), that allows to observe Raman scattering spectrum from extremely small volumes of Ge, even from one layer of quantum dots with the layer thickness of ~ 10 A. It is shown that Si diffuses into the Ge quantum dots from the Si spacer layers forming Ge_xSi_{1-x} solid solution, and Si concentration was estimated. It is revealed, that the frequency of Ge-Ge mode decreases in 10 1/cm at decreasing of the Ge layer thickness from 10 up to 6 A as a result of phonon size confinement effect.