  ZnSnN2 is an Earth-abundant analog 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 \emph{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 been able to explore a growth-temperature-composition space for
Zn(1+x)Sn(1-x)N(2) over the ranges 35-340 degrees C and 0.30-0.75 Zn/(Zn+Sn).
In this way, we were able to identify 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 degrees 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)). Furthermore, we report
evidence of a Burstein-Moss shift widening the apparent bandgap as cation
composition becomes increasingly Sn-rich, and tunable carrier density as a
function of cation composition (lower carrier density for higher Zn content),
which suggests the formation of defect complexes. Collectively, these findings
provide important insight into the fundamental properties of the Zn-Sn-N
material system, and also highlight the potential to utilize ZnSnN2 for
photovoltaics.
