Although the charge neutrality filter does not guarantee thermodynamic stability, these numbers give an idea of the enormous size of the quaternary PS chemical space, even when compared to other quaternary spaces that do not contain elements with the same versatility as phosphorus. Besides the advantage in size, what are the prospects of finding high quality semiconductors among quaternary PSs? An encouraging trend is that the number of already-known stable quaternary PSs exceeds the number of corresponding ternaries (Figure ). Hence, quaternary PSs should not have intrinsic problems with thermodynamic stability. Other promising features of the existing quaternary compounds are a higher fraction of materials with 3D structural dimensionality with respect to ternaries (Figure ), and a higher fraction of materials with a P/S = 1/4 ratio (Figure ), which typically have lower effective masses (Figure ) than the P/S = 1/3 case.