Silicon Photonics: Fundamentals and Devices

9.4 Raman Effect in Silicon

Research on Raman scattering in bulk silicon was initiated in the early 1970s, to study optical phonons in the material (see Temple and Hathaway in 4). The zone center optical phonon in crystalline Si (c-Si) is threefold degenerate and is responsible for a Stokes shift in the material. Figure 9.2 gives the observed Raman spectra. The scattered Stokes radiation is downshifted from the pump frequency by an amount equal to the zone center optical phonon frequency, and the shift is shown as 15.6 THz in Figure 9.2. The full width at half maximum (FWHM) of the spectra is 105 GHz, which corresponds to a response time of 10 ps. The second-order Stokes line is also observed, as indicated in Figure 9.2. However, its intensity is more than an order of magnitude lower.

Figure 9.2 Raman spectra in crystalline silicon. Reproduced with permission from [4]. Copyright (1973) American Physcial Society.