No abstract

The Electrochemical Atomic Layer Deposition (ECALD) methodology has been recently employed to synthesize thin films of ternary Cu-Zn sulfides, technologically relevant for photovoltaic semiconductors. This approach, which represents probably the first successful synthesis of a ternary Cu-Zn sulfide, consisted in alternate ECALD depositions of CuS and ZnS layers that yielded a compound with a Cu/Zn ratio of about 6, thus confirming the low contribution of Zn in ternary compound already evidenced in previous studies. This paper, which represents the logical sequel, shows that it is possible to establish a well defined relationship between deposition sequence and stoichiometry as done for the other ternary compounds containing Zn.

No abstract

Electrochemical Atomic Layer Deposition (E-ALD) technique has demonstrated to be a suitable process for growing compound semiconductors, by alternating the under-potential deposition (UPD) of the metallic element with the UPD of the non-metallic element. The cycle can be repeated several times to build up films with sub-micrometric thickness. We show that it is possible to grow, by E-ALD, Cu2S ultra-thin films on Ag(111) with high structural quality. They show a well ordered layered crystal structure made on alternating pseudohexagonal layers in lower coordination. As reported in literature for minerals in the Cu-S compositional field, these are based on CuS3 triangular groups, with layers occupied by highly mobile Cu ions. This structural model is closely related to the one of the low chalcocite. The domain size of such films is more than 1000 Å in lateral size and extends with a high crystallinity in the vertical growth direction up to more than 10 nm. E-ALD process results in the growth of highly ordered and almost unstrained ultra-thin films. This growth can lead to the design of semiconductors with optimal transport proprieties by an appropriate doping of the intra metallic layer. The present study enables E-ALD as an efficient synthetic route for the growth of semiconducting heterostructures with tailored properties.

Kesterite, Cu2ZnSn(S,Se)4, are considered promising materials for energy conversion devices, encompassing reduced production costs and low environmental risks. The Electrochemical Atomic Layer Epitaxy (ECALE) method was used to obtain compound semiconductors, in the form of thin films, whose composition belongs to the compositional field of kesterite. Namely, CuxSy and CuxZnyS thin films were considered in this study. Films were characterised through Scanning Electron Microscopy, for film morphology, and X-ray Absorption Spectroscopy, to determine the structure of the film, the metal valence states, the nature of the coordinating ligand. In particular, films are found to always exhibit a Cu2-xS type structure, where Zn is likely tetrahedrally coordinated. The role of the two transition metal cations in modulating the overall properties of the thin layer results fundamental and it opens interesting perspectives in the chemical tuning of the photovoltaic properties.