The influence of hydrogen gas anneals on the electrical properties of nominally undoped, oxygen-deficient SrTiO3-x single crystals was investigated. Titanium getter layers and vacuum anneals were used to obtain oxygen-deficient SrTiO3-x with a low electrical resistivity. These crystals showed an optical absorption peak at 2.92 eV and strong midinfrared absorption. Subsequent anneals at 800 °C in forming gas, which contained 10% hydrogen, returned the crystals into the insulating, transparent state. The mechanisms by which hydrogen anneals can compensate for the effects of oxygen vacancies in SrTiO3-x are discussed. The results show that forming gas anneals of stoichiometric SrTiO3 can lead to complex electrical conduction behavior.
Bibliographical noteFunding Information:
The authors thank Dr. Anderson Janotti and Professor Chris van de Walle for useful discussions. The research was supported by the National Science Foundation through the UCSB MRL (Award No. DMR05-20415) and DMR (Award No. DMR-0602244). One author (R. E.-H.) thanks the Alexander von Humboldt Foundation for support through the Feodor Lynen program.