Phase- and Thickness-Controlled Chemical Vapor Deposition of SnSe and SnSe2 Films: Thermodynamic and Kinetic Insights into Phase Selection

Phase selection among competing stoichiometric compounds during nonequilibrium vapor-phase growth remains a fundamental challenge because experimentally accessible growth parameters ultimately influence phase formation through both thermodynamic driving forces and atomic-scale kinetic processes. Here, we investigate phase selection between SnSe and SnSe2 during low-pressure chemical vapor deposition (CVD) by integrating systematic growth experiments, first-principles thermodynamic calculations, and ab initio molecular dynamics (AIMD) simulations. Systematic regulation of the relative Sn/Se chemical environment and growth temperature establishes distinct SnSe- and SnSe2-dominant growth regimes. Thermodynamic calculations show that SnSe is preferentially stabilized under Sn-rich conditions with low Se chemical potential, whereas increasing the Se chemical potential shifts the thermodynamic preference toward SnSe2. Complementary atomistic simulations reveal that increasing Se availability progressively promotes SnSe2-like local coordination, while elevated temperature enhances Sn−Se interdiffusion and redistributes Se toward more spatially dispersed, locally Se-deficient configurations. Building on the established phase-selective growth conditions, we further demonstrate independent thickness tunability through growth-time control, with SnSe and SnSe2 film thicknesses spanning 15−123 and 13.5−120 nm, respectively. Together, these results show that stoichiometry-dependent phase competition under nonequilibrium growth conditions reflects the combined effects of thermodynamic stability and atomic kinetics, while film thickness can be adjusted through growth-time control. These results provide insight into the relationship between growth conditions, phase selection, and film thickness in compositionally related layered chalcogenides.