  We demonstrate the successful fabrication on CaF$_2$ substrates of
FeSe$_{1-x}$Te$_{x}$ films with $0 \le x \le 1$, including the region of $0.1
\le x \le 0.4$, which is well known to be the "phase-separation region", via
pulsed laser deposition which is a thermodynamically non-equilibrium method. In
the resulting films, we observe a giant enhancement of the superconducting
transition temperature, $T_\mathrm{c}$, in the region of $0.1 \le x \le 0.4$:
the maximum value reaches 23 K, which is approximately 1.5 times as large as
the values reported for bulk samples of FeSe$_{1-x}$Te$_{x}$. We present a
complete phase diagram of FeSe$_{1-x}$Te$_{x}$ films. Surprisingly, a sudden
suppression of $T_\mathrm{c}$ is observed at $0.1<x<0.2$, while $T_\mathrm{c}$
increases with decreasing $x$ for $0.2 \le x < 1$. Namely, there is a clear
difference between superconductivity realized in $x=0-0.1$ and in $x \ge 0.2$.
To obtain a film of FeSe$_{1-x}$Te$_{x}$ with high $T_\mathrm{c}$, the controls
of the Te content $x$ and the in-plane lattice strain are found to be key
factors.
