  High quality Van der Waals chalcogenides are important for phase change data
storage, thermoelectrics, and spintronics. Using a combination of statistical
design of experiments and density functional theory, we clarify how the
out-of-equilibrium van der Waals epitaxial deposition methods can improve the
crystal quality of Sb2Te3 films. We compare films grown by radio frequency
sputtering and pulsed laser deposition (PLD). The growth factors that influence
the crystal quality for each method are different. For PLD grown films a thin
amorphous Sb2Te3 seed layer most significantly influences the crystal quality.
In contrast, the crystalline quality of films grown by sputtering is rather
sensitive to the deposition temperature and less affected by the presence of a
seed layer. This difference is somewhat surprising as both methods are
out-of-thermal-equilibrium plasma-based methods. Non-adiabatic quantum
molecular dynamics simulations show that this difference originates from the
density of excited atoms in the plasma. The PLD plasma is more intense and with
higher energy than that used in sputtering, and this increases the electronic
temperature of the deposited atoms, which concomitantly increases the adatom
diffusion lengths in PLD. In contrast, the adatom diffusivity is dominated by
the thermal temperature for sputter grown films. These results explain the wide
range of Sb2Te3 and superlattice crystal qualities observed in the literature.
These results indicate that, contrary to popular belief, plasma-based
deposition methods are suitable for growing high quality crystalline
chalcogenides.
