Figure shows the range of formation energy for each defect type in the neutral charge state. The atomic site indices corresponding to the highest and lowest formation energy are labeled in Figure . These sites are labeled in the supercell structure shown in Figure . The range of defect formation energies when all plausible charge states are considered are shown in Figures and for the Ba 0.75 Sr 1.25 CdP 2 alloy. In our convex hull analysis, we find 18 distinct four-phase stability regions of Ba 0.75 Sr 1.25 CdP 2 (Table ) in the quaternary Ba-Sr-Cd-P phase space. In reality, the alloy composition space i.e., x is continuous, but we perform the convex hull analysis assuming V Ba V (a) statistics of neutral defects Sr V Cd V P Cd P P Cd discrete alloy compositions that are marked in Figure . The overall conclusions about the dopability will remain unchanged even if a continuous composition space is considered in the convex hull analysis. In the context of n-type dopability, cation vacancies (V Ba , V Sr , V Cd ) are found to be the "killer" electron-compensating acceptor defects that may limit n-type doping. The formation of cation vacancies will be suppressed under cation-rich growth conditions. As such, we identified the four-phase stability region that corresponds to the most cation-rich conditions such that the ntype dopability window DE n is maximized.