An annealing study of an oxygen vacancy related defect in $SrTiO3$ substrates

The study addresses the stability of point defects in $SrTiO3$ (STO) during thin film processing using electron paramagnetic resonance (EPR) spectroscopy. In particular, the intensity of the $Fe3+VO$ EPR signal is monitored after various steps during the growth of STO films on STO substrates. Controlled $O2$ and vacuum heat treatments are also performed to clarify the fundamental mechanisms responsible for the effects of different processing steps. Comparison of results from film fabrication with those obtained during exposure to the control ambient shows that the presence of oxygen in the pretreatment growth atmosphere decreases the amount of the $Fe3+VO$ complex, but exposure to the low pressure environment of the growth chamber returns the signal to the original intensity. These results are consistent with accepted theories of oxygen vacancy diffusion. However, an unexpected decrease in the oxygen vacancy related signal is also observed during vacuum treatment of an as-received sample. Furthermore, the decrease occurs over the same temperature range as seen for an $O2$ anneal. The difference between the $O2$ and vacuum treatments is revealed in postannealing photoinduced EPR and resistivity measurements, which indicate that vacancy related centers change charge state during the $O2$ anneal and are not removed by oxygen. The effect of the vacuum treatment, though different from that of oxygen, is not yet clear as no charge state changes were induced after exposure to visible or ultraviolet radiation, but the conductivity of the samples changed.