Stability of point defects in SrTiO$_{3}$ substrates during thin film deposition

During deposition of multiferroic films on SrTiO$_{3}$, the substrate is subjected to ambients similar to those known to alter the oxygen vacancy concentration and conductivity. We have performed electron paramagnetic resonance (EPR) measurements on SrTiO$_{3}$ substrates at selected stages during film deposition as well as during controlled heat treatments. Fe$^{3+}$, Cr$^{3+}$ and an Fe-oxygen vacancy complex, Fe$^{3+}$V$_{o}$, were monitored during isochronal and isothermal vacuum (10$^{-6}$ Torr) and 1 atm O$_{2}$ heat treatments between 200 and 800 $^{\circ}$C. As expected, processing steps involving O$_{2}$ at 950 $^{\circ}$C reduces the concentration of Fe$^{3+}$V$_{o}$, consistent with the O$_{2}$ annealing study. Film deposition at 650 $^{\circ}$C, 5x10$^{-7}$ Torr with 10{\%} ozone returns the Fe$^{3+}$V$_{o}$ signal to the original intensity, consistent with vacuum treatments which follow 1 atm O$_{2}$ annealing. Surprisingly, isochronal and time-dependent vacuum and O$_{2}$ annealing produce the same trend for the Fe$^{3+}$V$_{o}$ signal for T $>$ 500 $^{\circ}$C. The results of all the studies suggest that electrostatic changes, as evidenced by variations in the intensity of Fe$^{3+}$ and Cr$^{3+}$, as well as oxygen vacancy migration can alter substrate characteristics during film growth.