  Thin film growth of iron chalcogenides by pulsed laser deposition (PLD) is
still a delicate issue in terms of simultaneous control of stoichiometry,
texture, substrate/film interface properties, and superconducting properties.
The high volatility of the constituents sharply limits optimal deposition
temperatures to a narrow window and mainly challenges reproducibility for
vacuum based methods. In this work we demonstrate the beneficial introduction
of a semiconducting FeSe$_{1\text{--}x}$Te$_x$ seed layer for subsequent
homoepitaxial growth of superconducting FeSe$_{1\text{--}x}$Te$_x$ thin film on
MgO substrates. MgO is one of the most favorable substrates used in
superconducting thin film applications, but the controlled growth of iron
chalcogenide thin films on MgO has not yet been optimized and is the least
understood. The large mismatch between the lattice constants of MgO and
FeSe$_{1\text{--}x}$Te$_x$ of about 11% results in thin films with a mixed
texture, that prevents further accurate investigations of a correlation between
structural and electrical properties of FeSe$_{1\text{--}x}$Te$_x$. Here we
present an effective way to significantly improve epitaxial growth of
superconducting FeSe$_{1\text{--}x}$Te$_x$ thin films with reproducible high
critical temperatures ($\geq$ 17 K) at reduced deposition temperatures (200
{\deg}C - 320 {\deg}C) on MgO using PLD. This offers a broad scope of various
applications.
