The impact of oxygen vacancies on local tunneling properties across rf-sputtered MgO thin films was investigated by optical absorption spectroscopy and conducting atomic force microscopy. Adding O2 to the Ar plasma during MgO growth alters the oxygen defect populations, leading to improved local tunneling characteristics such as a lower density of current hotspots and a lower tunnel current amplitude. We discuss a defect-based potential landscape across ultrathin MgO barriers.
Bibliographical noteFunding Information:
We thank Y. Yin for assistance with optical experiments and D. Halley and S. J. Park for stimulating discussions. This work was supported by the EC FP6 (Grant No. NMP3-CT-2006-033370), the French ANR (Grants No. ANR-06-NANO-033-01 and No. ANR-09-JCJC-0137), and by the Korean MEST (Grant No. 2010K000339 from CNMT under 21st Century Frontier R&D Programs; Grant No. NRF 2010-0020416).