Evolution of Raman spectra as a function of layer thickness in ultra-thin InSe films

Experimentally, when compared with III-V, II-VI, or IV-IV layered systems, the InSe Raman spectrum does not change very much as a function of the number of InSe layers. A simple linear chain model is sufficient to explain this effect. In our model, two parameters are used to characterize Raman spectra: the halfwidth Γ characterizing the sample quality and the coherence length Λ determined by the sample thickness n. Our analysis shows that the coherence length Λ is linear in n. We obtain a fair agreement between computed and experimental Raman spectra.