Oxygen-Induced Phase Separation in Sputtered Cu-Sn-I-O Thin Films

Authors：Zollner, Eva M.; Selle, Susanne; Yang, Chang; Ritter, Konrad; Eckner, Stefanie; Welter, Edmund; Grundmann, Marius; Schnohr, Claudia S.^*

Source：Physica Status Solidi (A) Applications and Materials, 2023, 220(5).

DOI：10.1002/pssa.202200646

• amorphous semiconductors
• CuI
• CuSnI
• electron microscopy
• X-ray absorption spectroscopy

Amorphous Cu-Sn-I is a promising p-type transparent semiconductor. Therefore, herein, composition and structure of sputtered Cu-Sn-I thin films with varying thickness and Sn content are investigated by different electron microscopy techniques, energy-dispersive X-ray spectroscopy, and X-ray absorption spectroscopy at the Cu, Sn, and I K-edge. After exposure to air, the sputtered films are found to contain significant amounts of oxygen, leading to a complete phase separation of the resulting Cu-Sn-I-O films. Spatially-resolved compositional analysis and high-resolution transmission electron microscopy reveal that one phase consists of crystalline gamma-CuI while the other phase is composed of amorphous Cu-Sn-O, most likely a mixture of SnO2 and Cu2O/CuO. X-ray absorption spectroscopy confirms that the local structural environment of the Sn and I atoms is similar to that in amorphous SnO2 and crystalline CuI, respectively. In contrast, the X-ray absorption near edge structure and the extended X-ray absorption fine structure of the Cu K-edge both demonstrate that Cu atoms are not only bonded to I but also to O atoms. The incorporation of oxygen into the sputtered films thus completely alters the material and therefore clearly needs to be inhibited.

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