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ALD Zn(O,S) Thin Films’ Interfacial Chemical and Structural Configuration Probed by XAS

Anup Lal Dadlani, Shinjita Acharya, Orlando Trejo, Fritz B Prinz, Jan Torgersen, "ALD Zn (O, S) thin films’ interfacial chemical and structural configuration probed by XAS", APPLIED MATERIALS AND INTERFACES, vol. 8, pp. 14323-14327, 2016.

The ability to precisely control interfaces of atomic layer deposited (ALD) zinc oxysulfide (Zn(O,S)) buffer layers to other layers allows precise tuning of solar cell performance. The O K- and S K-edge X-ray absorption near edge structure (XANES) of ∼2–4 nm thin Zn(O,S) films reveals the chemical and structural influences of their interface with ZnO, a common electrode material and diffusion barrier in solar cells. We observe that sulfate formation at oxide/sulfide interfaces is independent of film composition, a result of sulfur diffusion toward interfaces. Leveraging sulfur’s diffusivity, we propose an alternative ALD process in which the zinc precursor pulse is bypassed during H2S exposure. Such a process yields similar results to the nanolaminate deposition method and highlights mechanistic differences between ALD sulfides and oxides. By identifying chemical species and structural evolution at sulfide/oxide interfaces, this work provides insights into increasing thin film solar cell efficiencies.