Strain and Intermixing in Single Ge/Si Quantum Dots Observed by Tip-enhanced Raman Spectroscopy

Tip-enhanced Raman spectra of as-grown self-assembled Ge/Si quantum dots have been observed with nano-scale spatial resolution. It is found that the Ge-Ge and Si-Ge modes in the Raman spectra were significantly enhanced only when the tip was on the Ge/Si dots. The Ge content in a single dot was estimated from the relative intensity of the Ge-Ge and Si-Ge modes. It is also found that the Si substrate peak at 520 cm(-1) was shifted considerably in the neighborhood of the Ge/Si dots. This means that the Si substrate suffers stress around the dots.