Abstract
The dependence of the phonon frequencies of the quaternaryCu(In1−xGax)5Se8 films with tetragonal structure on the Ga content have beensystematically investigated by means of Raman scattering. The dominantA1 modeshifts from 151 cm−1 for CuIn5Se8 to 160 cm−1 for CuGa5Se8 in an approximately polynomial but not linear curve, because different typesof local tetrahedral cationic clusters around Se distribute in the defectcrystal structures. The vibrational modes in the low-frequency region below125 cm−1 clearly show one-mode behaviour, whereas significant changes in the frequency range from 160 to235 cm−1 indicate defect-induced structural disorder and show two-mode behaviourdue to Ga addition. Additionally, the quenching of the Raman band at174 cm−1 for the Ga-rich films reveals that this mode should most probably originatefrom other similar localized structure phases in chalcopyrite-relatedCuIn5Se8 butnot CuGa5Se8, due to the Ga inhibition effect. Such results should be ascribed to asymmetric distributionof Ga and In on a microscopic scale, resulting in the different properties of bonds betweenlocal clusters.
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