Raman scattering and infrared absorption in multiple boron-doped Ge dots

Abstract

Multiple boron-doped Ge quantum dots are investigated. The structure, which consists of 20 periods of Ge quantum dots stacked with 6 nm Si spacers, is grown on a Si (100) substrate by solid source molecular beam epitaxy. Cross-sectional transmission electron microscopy and atomic force microscopy are 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, the strong inter-sub-level transition in the Ge quantum dots is observed. The transition is further confirmed by Fourier transform infrared spectroscopy using a waveguide geometry. The observed peak at 5 μm in the infrared absorption spectrum is consistent with that in the Raman spectrum and attributed to the transition between the first two heavy hole band states of the Ge quantum dots. The polarization dependence measurement is used to study the nature of the transitions. This study suggests the possible use of Ge quantum dots for infrared detector application.