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.
Controlling site
disorder in ternary and multinary compounds enables
tuning optical and electronic properties at fixed lattice constants
and stoichiometries, moving beyond many of the challenges facing binary
alloy systems. Here, we consider possible enhancements to energy-related
applications through the integration of disorder-tunable materials
in devices such as light-emitting diodes, photonics, photovoltaics,
photocatalytic materials, batteries, and thermoelectrics. However,
challenges remain in controlling and characterizing disorder. Focusing
primarily on II–IV–V2 materials, we identify
three metrics for experimentally characterizing cation site disorder.
Complementary to these experiments, we discuss simulation methods
to understand disordered materials. Nonidealities, such as off-stoichiometry
and oxygen incorporation, can occur while synthesizing metastable
disordered materials. While nonidealities may seem undesirable, we
describe how if harnessed they could provide another knob for tuning
disorder and subsequently properties. To illustrate the effects of
disorder on device-relevant properties, we provide case examples of
disordered materials and their potential in device applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.