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

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. Cros s-sectional transmission electron;microscopy: and atomic force microscopy a re used to characterize the structural properties of these ae dots. Raman s pectrum shows a downward shift of the Ge-Ge mode, which is attributed to th e phonon confinement in the Ge dots. From polarization dependent Raman spec tra, the strong inter-sub-level transition in the Ge quantum dots is observ ed. The transition is further confirmed by Fourier transform infrared spect roscopy using a waveguide geometry. The observed peak at 5 mu m in the infr ared absorption spectrum is consistent with that in the Raman spectrum and attributed to the transition:between the first two heavy hole band states o f the Ge quantum dots. The polarization dependence measurement is used to s tudy the nature of the transitions. This study suggests the possible use of Ge quantum dots for infrared detector application. (C) 1999 American Vacuu m Society. [S0734-2101(99)04304-3].