Raman scattering from a self-organized Ge dot superlattice

We present a Raman scattering study of a self-organized Ge dot superlattice. The structure, which consists of 20 periods of Ge quantum dots sandwiched by 6 nm Si spacers, is grown on a Si (100) substrate by solid source molecular beam epitaxy. Cross-sectional transmission electron microscopy is used to characterize the structural properties of these Ge dots. Raman spectrum shows a downward shift of the Ge–Ge mode, which is attributed to the phonon confinement in the Ge dots. From polarization dependent Raman spectra, strong inter-sub-level transition in the Ge quantum dots is observed. From a simple calculation, the observed peak at 1890 cm−1 in the polarized spectrum is attributed to the transition between the first two heavy hole states of the Ge quantum dots.