First-principles study of vibrational modes and Raman spectra in P-doped Si nanocrystals

We have studied the vibrational modes and Raman spectra of P-doped Si nanocrystals using pseudopotential density functional theory and the Placzek approximation. We find that Si nanocrystal vibrations are largely unaffected by the introduction of P dopants. However, the Raman spectra of doped nanocrystals are enhanced relative to those of pristine nanocrystals, and demonstrate a strong dependence on dopant position. Thus, Raman has the potential of being developed as a tool for probing the location of the dopant within the nanocrystal. Our analysis shows that vibrational modes involving atoms in the vicinity of the dopant give the largest contributions to the Raman spectra.