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Direct observation of a two-dimensional hole gas at oxide interfaces

Abstract

The discovery of a two-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 interface1 has resulted in the observation of many properties2,3,4,5 not present in conventional semiconductor heterostructures, and so become a focal point for device applications6,7,8. Its counterpart, the two-dimensional hole gas (2DHG), is expected to complement the 2DEG. However, although the 2DEG has been widely observed9, the 2DHG has proved elusive. Herein we demonstrate a highly mobile 2DHG in epitaxially grown SrTiO3/LaAlO3/SrTiO3 heterostructures. Using electrical transport measurements and in-line electron holography, we provide direct evidence of a 2DHG that coexists with a 2DEG at complementary heterointerfaces in the same structure. First-principles calculations, coherent Bragg rod analysis and depth-resolved cathodoluminescence spectroscopy consistently support our finding that to eliminate ionic point defects is key to realizing a 2DHG. The coexistence of a 2DEG and a 2DHG in a single oxide heterostructure provides a platform for the exciting physics of confined electron–hole systems and for developing applications.

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Fig. 1: Atomically abrupt p-type interface in epitaxially grown STO/LAO/STO heterostructure.
Fig. 2: Electrical transport properties of the top and bottom interfaces in the STO/LAO/STO heterostructure.
Fig. 3: Charge distribution in the STO/LAO/STO heterostructure.
Fig. 4: Oxygen-vacancy distribution in the STO/LAO/STO heterostructure.

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Acknowledgements

This work was supported by the National Science Foundation (NSF) under DMREF Grant number DMR-1629270, AFOSR under award number FA9550-15-1-0334 and AOARD under award number FA2386-15-1-4046. Transport measurement at the University of Wisconsin-Madison was supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, under award number DE-FG02-06ER46327. Research at the University of Nebraska-Lincoln was supported by the NSF MRSEC (Grant no. DMR-1420645). T.J.A. and L.J.B. acknowledge support from NSF grant DMR 1305193. Use of the Advanced Photon Source was supported by the US DOE, Office of Science, Office of Basic Energy Sciences, under Contract no. DE-AC02-06CH11357. STEM and in-line electron holography works by S.H.O. were supported by the Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (NRF-2015M3D1A1070672) and NRF grant funded by the Korea government (NRF-2015R1A2A2A01007904).

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H.L. and C.B.E. conceived the project. C.B.E., M.S.R., E.Y.T., S.H.O. and L.J.B. supervised the experiments. H.L., J.W.L. and C.B.E. fabricated and characterized the thin-film samples. N.C. and M.S.R. carried out the electrical transport measurements. J.L., B.P., J.S. and S.H.O. carried out the STEM and in-line holography measurements. T.J.A. and B.N. performed the DR-CLS measurements. T.R.P. and E.Y.T. performed the theoretical calculations. H.Z. performed the synchrotron diffraction measurements. H.L., N.C., J.L., T.A., T.R.P., H.Z. and C.B.E. prepared the manuscript. C.B.E. directed the overall research.

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Correspondence to C. B. Eom.

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Lee, H., Campbell, N., Lee, J. et al. Direct observation of a two-dimensional hole gas at oxide interfaces. Nature Mater 17, 231–236 (2018). https://doi.org/10.1038/s41563-017-0002-4

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