Anharmonic interactions and temperature effects in Raman spectra of Si nanostructures

•Additional Raman band from Si crystallites, arising at high excitation power, is studied.•Model proposed assumes biaxial strain in laser-heated crystallites splits F2g, Eg phonon states.•Fermi resonance between acoustical modes of L-point and optical mode of Г-point is supposed.

An additional Raman phonon band observed for Si crystallites at high excitation power is studied theoretically. Laser-induced heating is supposed to induce stress in crystallites, leading to splitting of degenerated F2g, Eg phonon states into А′ and А′′ ones. The enhancement of anharmonicity effects expected at high temperature may lead to strong coupling between А′ (А′′) fundamental modes with combination tones arising at splitting F2g, Eg states. As a result, the Fermi resonance interaction between the optical modes from Г-point and sum of acoustic modes from L-point can explain the temperature behavior of experimentally observed additional optical phonon band in Raman spectra of Si nanocrystallites.