A sulfonitride transparent conductive thin film with ultra-high refractive index

TL;DR

This paper reports the first thin-film synthesis of Zr2SN2, a metal sulfonitride with an ultra-high refractive index and combined optical transparency and electrical conductivity, opening new avenues for transparent conductors.

Contribution

It introduces a novel thin-film growth method for metal sulfonitride compounds, specifically Zr2SN2, with exceptional optical and electrical properties.

Findings

Zr2SN2 films are transparent across most of the visible spectrum.

Zr2SN2 exhibits a high average refractive index of 2.95.

Zr2SN2 shows degenerate n-type conductivity with high carrier density.

Abstract

With the rise of AI-assisted materials screening, extraordinary properties are now frequently predicted in experimentally uncharted material systems, highlighting the need to develop new synthesis methods for unconventional materials beyond the classic bulk powder form. Here, we establish the first thin-film growth route for any metal sulfonitride compound by realizing Zr2SN2 films with a rare and compelling combination of optical and electrical properties. Zr2SN2 is transparent across most of the visible range while exhibiting a very high average refractive index of 2.95 in the visible, exceeding expectations based on conventional refractive index-bandgap scaling. Importantly, the same Zr2SN2 film shows degenerate n-type conductivity with carrier density above 10^20 cm-3 and intragrain mobility above 8 cm2V-1s-1, approaching those of established transparent conductive oxides. Zr2SN2 thus demonstrates that strong light-matter interaction, optical transparency and electrical conductivity can be reconciled within a single material platform, revealing a new class of high-refractive-index transparent conductors.