Design of ternary alkaline-earth metal Sn(II) oxides with potential good p-type conductivity

TL;DR

This study uses first-principles calculations to identify new stable ternary alkaline-earth metal Sn(II) oxides with promising electronic properties for p-type conductivity, relevant for optoelectronic devices.

Contribution

It introduces two stable Sn(II)-based compounds, SrSn2O3 and BaSn2O3, with tunable electronic properties, expanding the material space for p-type transparent conductors.

Findings

SrSn2O3 and BaSn2O3 are thermodynamically stable under Sn-rich conditions.

These compounds exhibit band gaps suitable for optoelectronic applications.

Their electronic properties can be tuned by structural modifications.

Abstract

Oxides with good p-type conductivity have been long sought after to achieve high performance all-oxide optoelectronic devices. Divalent Sn(II) based oxides are promising candidates because of their rather dispersive upper valence bands caused by the Sn-5s/O-2p anti-bonding hybridization. There are so far few known Sn(II) oxides being p-type conductive suitable for device applications. Here, we present via first-principles global optimization structure searches a material design study for a hitherto unexplored Sn(II)-based system, ternary alkaline-earth metal Sn(II) oxides in the stoichiometry of MSn2O3 (M = Mg, Ca, Sr, Ba). We identify two stable compounds of SrSn2O3 and BaSn2O3, which can be stabilized by Sn-rich conditions in phase stability diagrams. Their structures follow the Zintl behaviour and consist of basic structural motifs of SnO3 tetrahedra. Unexpectedly they show distinct electronic properties with band gaps ranging from 1.90 (BaSn2O3) to 3.15 (SrSn2O3) eV, and hole effective masses ranging from 0.87 (BaSn2O3) to above 6.0 (SrSn2O3) m0. Further exploration of metastable phases indicates a wide tunability of electronic properties controlled by the details of the bonding between the basic structural motifs. This suggests further exploration of alkaline-earth metal Sn(II) oxides for potential applications requiring good p-type conductivity such as transparent conductors and photovoltaic absorbers.