Structure and properties of ZnSxSe1−x thin films deposited by thermal evaporation of ZnS and ZnSe powder mixtures

• Published in: Materials research express Vol. 2; no. 2
• Main Authors: Valeev, R G, Romanov, E A, Vorobiev, V L, Mukhgalin, V V, Kriventsov, V V, Chukavin, A I, Robouch, B V
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.02.2015
• Subjects: band gap; compounds; EXAFS spectroscopy; Raman spectroscopy; thermal evaporation of ZnS and ZnSe powders mixture; thin films of ZnS; x-ray diffraction
• ISSN: 2053-1591
• DOI: 10.1088/2053-1591/2/2/025006

Interest to ZnSxSe1−x alloys is due to their band-gap tunability varying S and Se content. Films of ZnSxSe1−x were grown evaporating ZnS and ZnSe powder mixtures onto SiO2, NaCl, Si and ITO substrates using an original low-cost method. X-ray diffraction patterns and Raman spectroscopy, show that the lattice structure of these films is cubic ZnSe-like, as S atoms replace Se and film compositions have their initial S Se ratio. Optical absorption spectra show that band gap values increase from 2.25 to 3 eV as x increases, in agreement with the literature. Because S atomic radii are smaller than Se, EXAFS spectra confirm that bond distances and Se coordination numbers decrease as the Se content decreases. The strong deviation from linearity of ZnSe coordination numbers in the ZnSxSe1−x indicate that within this ordered crystal structure strong site occupation preferences occur in the distribution of Se and S ions. The behavior is quantitatively confirmed by the strong deviation from the random Bernoulli distribution of the three sight occupation preference coefficients of the strained tetrahedron model. Actually, the ternary ZnSxSe1−x system is a bi-binary (ZnS+ZnSe) alloy with evanescent formation of ternary configurations throughout the x-range.