Observation of resonant Raman scattering at the Si L2,3 core exciton.

The resonant soft-x-ray emission spectra at the Si ${\mathit{L}}_{2,3}$ core exciton have been measured at 18 K by using synchrotron radiation. As an excitation light source, a very high-resolution monochromator with the undulator was used. The Raman scattering whose energy shifts in proportion to the excitation energy is found below the ${\mathit{L}}_{2,3}$ absorption edge. The intensity of the Raman scattering increases rapidly as the excitation energy comes close to the ${\mathit{L}}_{2,3}$ core exciton. It is found that the Raman scattering resonates at the ${\mathit{L}}_{2,3}$ core exciton which is made around the ${\mathit{X}}_{1}$ conduction minimum. The elementary excitation of the Raman scattering is the valence exciton that is a transition from ${\mathit{X}}_{1}$ or ${\mathit{X}}_{4}$ points in the valence band to the ${\mathit{X}}_{1}$ conduction minimum. The ${\mathit{X}}_{4}$ valence exciton has a characteristic excitation-energy dependence, so that it becomes broad and weak as the resonant Raman process goes to the ordinary Raman process. \textcopyright{} 1996 The American Physical Society.