Design of Metastable Tin Titanium Nitride Semiconductor Alloys

We report on design of optoelectronic properties in previously unreported metastable tin titanium nitride alloys with spinel crystal structure. Theoretical calculations predict that Ti alloying in metastable Sn₃N₄ compound should improve hole effective mass by up to 1 order of magnitude, while other optical bandgaps remains in the 1-2 eV range up to x ∼ 0.35 Ti composition. Experimental synthesis of these metastable alloys is predicted to be challenging due to high required nitrogen chemical potential (Δμ_N ≥ +1.0 eV) but proven to be possible using combinatorial cosputtering from metal targets in the presence of nitrogen plasma. Characterization experiments confirm that thin films of such (Sn_1-xTi_x)₃N₄ alloys can be synthesized up to x = 0.45 composition, with suitable optical band gaps (1.5-2.0 eV), moderate electron densities (10¹⁷ to 10¹⁸ cm^-3), and improved photogenerated hole transport (by 5×). Overall, this study shows that it is possible to design the metastable nitride materials with properties suitable for potential use in solar energy conversion applications.