Sputter deposition and structural characterization of BiCuSeO epitaxial films on (001)/(110) SrTiO₃ substrates

BiCuSeO epitaxial films were grown on (001)/(110) SrTtO₃ (STO) substrates by RF magnetron sputter deposition. A sputter power over 40 W was needed to transfer target composition to substrate, leading to a fast deposition rate over 17.5 nm/min. The films grown on (001) STO at 100−150 °C showed a dominant [110] orientation instead of [001], which was what expected in view of the smallest lattice misfit and perfect match in symmetry between (001) BiCuSeO and (001) STO. This was caused by slow film growth along c-axis that could not follow the fast deposition rate, whereas a fair lattice misfit, combined with strong bonding along directions vertical to c-axis, entails the growth along [110] at low temperature. Preferred [001] orientation only occurred at high temperature (>350 °C) when the kinetic process was accelerated. However, high temperature and the fast deposition rate imposed by the required sputter power led to the growth of multiple orientations. Epitaxial growth of (001) BiCuSeO film on (001) STO was achieved after the deposition rate was reduced to 0.67 nm/min by a periodically opening and closing shutter installed in front of sputter target. Interestingly, (001) BiCuSeO epitaxial film could be grown on (110) STO at a fast deposition rate of 15 nm/min. Such films on (110) STO had to be grown at higher temperature (∼500 °C). In contrast to (001) STO, (110) STO did not had good lattice match with any BiCuSeO orientation other than [001], so fast kinetic process only promoted the growth of single [001] orientation.