Optical properties of quaternary kesterite-type Cu2Zn(Sn1−xGex)S4 crystalline alloys: Raman scattering, photoluminescence and first-principle calculations

• Published in: RSC advances Vol. 6; no. 72; pp. 67756 - 67763
• Main Authors: Valakh, M. Ya, Litvinchuk, A. P, Dzhagan, V. M, Yukhymchuk, V. O, Havryliuk, Ye. O, Guc, M, Bodnar, I. V, Izquierdo-Roca, V, Pérez-Rodríguez, A, Zahn, D. R. T
• Format: Journal Article
• Language: English
• Published: 18.07.2016
• Subjects: Alloy systems; Alloys; Mathematical analysis; Photoluminescence; Raman scattering; Semiconductors; Sulfur; Transformations
• ISSN: 2046-2069
• DOI: 10.1039/c6ra13608g

The transformation of the vibrational spectrum of Cu 2 Zn(Sn 1− x Ge x )S 4 single crystals over the entire composition range (0 ≤ x ≤ 1) is studied experimentally by low-temperature Raman scattering and photoluminescence spectroscopies, as well as theoretically in the framework of density functional theory (DFT). It is shown that unlike "classic" mixed binary II-VI and III-V compounds, which are characterized by either one- or two-mode behavior of spectra transformation upon composition variation, the vibrational modes of the quaternary semiconductor Cu 2 Zn(Sn 1− x Ge x )S 4 exhibit both types of behavior within the same alloy system. DFT calculations reveal that the two-mode transformation is in fact observed for the vibrational modes, which possess a very small dispersion across the Brillouin zone, that is typical for a molecular crystal. These modes are due to the "breathing" motion of sulfur within GeS 4 and SnS 4 tetrahedra. The effects of structural (positional) disorder of mixed crystals are analyzed based on Raman scattering as well as photoluminescence results. The transformation of the vibrational spectrum of Cu 2 Zn(Sn 1− x Ge x )S 4 single crystals over the entire composition range (0 ≤ x ≤ 1) is studied experimentally as well as theoretically.