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Royal Society of Chemistry, Journal of Materials Chemistry C Materials for optical and electronic devices, 42(3), p. 11017-11028, 2015

DOI: 10.1039/c5tc02663f

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Combinatorial Insights into Doping Control and Transport Properties of Zinc Tin Nitride

This paper is available in a repository.
This paper is available in a repository.

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Abstract

ZnSnN 2 is an Earth-abundant semiconductor analogous to the III-Nitrides with potential as a solar absorber due to its direct bandgap, steep absorption onset, and disorder-driven bandgap tunability. Despite these desirable properties, discrepancies in the fundamental bandgap and degenerate n-type carrier density have been prevalent issues in the limited amount of literature available on this material. Using a combinatorial RF co-sputtering approach, we have explored a growth-temperature-composition space for Zn 1+x Sn 1-x N 2 over the ranges 35–340 • C and 0.30–0.75 Zn/(Zn+Sn). In this way, we identified an optimal set of deposition parameters for obtaining as-deposited films with wurtzite crystal structure and carrier density as low as 1.8 x 10 18 cm-3. Films grown at 230 • C with Zn/(Zn+Sn) = 0.60 were found to have the largest grain size overall (70 nm diameter on average) while also exhibiting low carrier density (3 x 10 18 cm-3) and high mobility (8.3 cm 2 V-1 s-1). Using this approach, we establish the direct bandgap of cation-disordered ZnSnN 2 at 1.0 eV. Furthermore, we report tunable carrier density as a function of cation composition, in which lower carrier density is observed for higher Zn content. This relationship manifests as a Burstein-Moss shift widening the apparent bandgap as cation composition moves away from Zn-rich. Collectively, these findings provide important insight into the fundamental properties of the Zn-Sn-N material system and highlight the potential to utilize ZnSnN 2 for photovoltaics.