Effects of hydrostatic pressure on Raman scattering in Ge quantum dots

Raman scattering under hydrostatic pressure is used to investigate the phonon modes of self-organized Ge quantum dots (QD’s) grown by solid source molecular-beam epitaxy. The pressure dependence of Ge-Ge phonon and Si acoustical-overtone (2TA) modes are studied from 0 to 67 kbar at room temperature. Our results show that the overlapping spectra of the Ge-Ge phonon and Si 2TA modes occur around $303\hspace{0.5em}{\mathrm{cm}}_{-1}$ at ambient pressure which can be resolved at relatively low pressure of about 3 kbar. The linear pressure coefficient of Ge-Ge phonon mode in QD’s is found to be $0.29\hspace{0.5em}{\mathrm{cm}}_{-1}/\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r},$ which is slightly smaller than the corresponding quantity in bulk Ge.