Raman scattering by intervalley carrier-density fluctuations in n-type Ge: Uniaxial stress and resonance effects

We report the observation of light scattering by intervalley density fluctuations in n-type germanium. This scattering appears as a Lorentzian tail near the exciting laser frequency extending up to 500 cm-1. Application of a uniaxial stress of 15 kbar along [111] results in the disappearance of this scattering, thus confirming the assignment to intervalley fluctuations. The effect has been shown to resonate near the E1 interband gap of Ge (2.1 eV). An analysis of the dependence of the scattering on photon wavelength suggests that the effect is due mainly to intravalley diffusion and not to intervalley scattering.