Temperature dependence of Raman scattering in amorphous films of In_1-xSe_x alloys

Raman scattering (RS) in amorphous films of In_1-xSe_x with 0.70 ≥ x ≥ 0.38 has been studied in backscattering geometry with the use of a single channel Raman spectrometer at room and 10 K temperatures. The recorded RS spectra reveal dominant vibrational density-of-states character. They exhibit a continuum, spanning the Rayleigh line up to a shoulder at about 250 cm^-1, that moves towards lower frequencies as x decreases from 0.70 to 0.38. The bands at about 104, 125 and at 143 and 237 cm^-1 are attributed to In-In, Se₈ ring molecules and Se-chain oscillations, respectively. The structure of In_1-xSe_x alloys is deduced to be a continuous random network based on InSe_4/2 tetrahedral clusters interconnected by Se atoms at the shared corners or local Se-chain fragments or Se₈ rings. With growing In content, some Se atoms in such clusters are replaced by In atoms to an extent dependent on In content. The disappearance of the 143 and 237 cm^-1 bands in the low temperature spectra taken on the In_0.30Se_0.70 film is attributed to the contraction of interatomic bonds, making conditions favorable for breaking Se polymer chains and Se₈ ring molecule formation.