Combinatorial Synthesis of Magnesium Tin Nitride Semiconductors

Nitride
materials feature strong chemical bonding character that
leads to unique crystal structures, but many ternary nitride chemical
spaces remain experimentally unexplored. The search for previously
undiscovered ternary nitrides is also an opportunity to explore unique
materials properties, such as transitions between cation-ordered and
-disordered structures, as well as to identify candidate materials
for optoelectronic applications. Here, we present a comprehensive
experimental study of MgSnN2, an emerging II–IV–N2 compound, for the first time mapping phase composition and
crystal structure, and examining its optoelectronic properties computationally
and experimentally. We demonstrate combinatorial cosputtering of cation-disordered,
wurtzite-type MgSnN2 across a range of cation compositions
and temperatures, as well as the unexpected formation of a secondary,
rocksalt-type phase of MgSnN2 at Mg-rich compositions and
low temperatures. A computational structure search shows that the
rocksalt-type phase is substantially metastable (>70 meV/atom)
compared
to the wurtzite-type ground state. Spectroscopic ellipsometry reveals
optical absorption onsets around 2 eV, consistent with band gap tuning
via cation disorder. Finally, we demonstrate epitaxial growth of a
mixed wurtzite-rocksalt MgSnN2 on GaN, highlighting an
opportunity for polymorphic control via epitaxy. Collectively, these
findings lay the groundwork for further exploration of MgSnN2 as a model ternary nitride, with controlled polymorphism, and for
device applications, enabled by control of optoelectronic properties
via cation ordering.