  We report the synthesis of tetragonal $\mathrm{FeS}_x\mathrm{Se}_{1-x}$ films
($x \leq 0.78$) by pulsed-laser deposition. To fabricate the tetragonal alloy
films with tetragonal FeSe and hexagonal FeS targets, we adopted an alternate
deposition technique with FeSe buffer layer on MgO(001). The overall film
composition is controlled by the thickness ratio of FeS / FeSe layers. The
out-of-plane lattice parameter of the films follows Vegard's law, demonstrating
homogeneous alloying by inter-diffusion. The sulfur solid solubility reaches $x
= 0.78$ in the $\mathrm{FeS}_x\mathrm{Se}_{1-x}$ films, which is by far larger
than $x \approx 0.40$ in bulk governed by the tetragonal phase instability.
