RAMAN-SCATTERING STUDIES OF PHONONS IN QUASI-PERIODIC SUPERLATTICES BASED ON GENERALIZATIONS OF THE FIBONACCI SEQUENCE

We report Raman scattering measurements on several different SiSiGe quasiperiodic superlattices. The structures, which are generalizations of the well known Fibonacci superlattices, are defined by the recursion relation Sj=(Sj-1)nSj-2 The structure factor for this structure exhibits peaks at wavevectors klm≡ 2π(l+mτ) d where d is a length that characterize irrational number given by τ= [n+(n2+4) 1 2] 2. We calculate the acoustic phonon Raman spectrum using the photoel in the plane wave approximation. The effect of self-similarity is clearly seen in the expression for the structure factor. Raman spectra on several samples demonstrate the effect of self-similarity on the spectrum, as well as differences between the structures with different n. The wavelength dependence of the Raman spectrum demonstrates the limits of the model we are using to calculate the Raman spectrum. © 1990.