Pyrite thin films on amorphous substrates: Interaction with the substrate and doping effects

Recent published literature dealing with FeS pyrite (thin films and single crystals) faces a few and relevant issues: the low photovoltage presented by pyrite (mainly related to the singular nature of its surface), the not yet clearly defined way of making available n and p type reliable samples and the relevance of their stoichiometry. To address the second and third issues, Fe thin films, Ti/Fe and Co/Fe bilayers deposited on sodalime glass and amorphous quartz substrates have been sulfurated at different temperatures (T) (T ≲ 600C) during 20 h to obtain pyrite thin films. Seebeck coefficient and Hall Effect measurements have been carried out at room temperature with the sulfurated samples. It has been found that sulfurated Ti/Fe on sodalime glass presents a change of the Seebeck coefficient sign (from negative to positive) due to a strong interaction of the Ti layer with the substrate, which is not present in the Ti/Fe samples deposited on amorphous quartz. As a consequence of the interaction, a new TiO layer is formed between the sodalime glass substrate and the pyrite layer. Sulfurated Co/Fe bilayers on sodalime glass show a coherent behavior according to the obtained results and previously published works. They all appear to be n-type semiconductors when T ≳ 175C. Non-intentionally doped Fe thin films on sodalime glass behave in a non-conclusive fashion from the point of view of their electrical transport characterization. The Seebeck coefficient (S) of the sulfurated films appear to be S > 0 for all values of T. However, the value and sign of the Hall constant behave in a non-reproducible way. Results are discussed on the light of present knowledge of synthetic pyrite thin films growth and doping.The authors thank technical support from Mr. F. Moreno. Financial support by MINECO-FEDER (MAT2015-65203R) is acknowledged and the project INFANTE (PIE 201550E072) is also recognized. Carlos Morales thanks the Ministerio de Educación Cultura y Deporte of Spain for the FPU grant