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Through systematic control of the Nd concentration, we show that the carrier density of the two-dimensional electron gas (2DEG) in SrTiO3/NdTiO3/SrTiO3(001) can be modulated over a wide range. We also demonstrate that the NdTiO3 in heterojunctions without a SrTiO3 cap is degraded by oxygen absorption from air, resulting in the immobilization of donor electrons that could otherwise contribute to the 2DEG. This system is, thus, an ideal model to understand and control the insulator-to-metal transition in a 2DEG based on both environmental conditions and film-growth processing parameters.
Bibliographical noteFunding Information:
The authors thank Professor Andre Mkhoyan for helpful discussions. This work at the University of Minnesota was supported primarily by the AFOSR young investigator program (Grant No. FA9550-16-1-0205) and in part by the UMN MRSEC under Grant No. DMR-1420013. We also acknowledge use of facilities at the UMN Characterization Facility and the Nanofabrication Center. The XPS work and computational modeling at PNNL was supported by the U.S. Department of Energy, Office of Science, Division of Materials Sciences and Engineering under Award No. 10122. R. C. was supported by the Linus Pauling Distinguished Post-Doctoral Fellowship at Pacific Northwest National Laboratory (PNNL LDRD Grant No. PN13100/2581). The PNNL work was performed in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at PNNL.
© 2016 American Physical Society.
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