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Probing electron transport across a LSMO/Nb:STO heterointerface at the nanoscale

K. G. Rana, S. Parui, and T. Banerjee
Phys. Rev. B 87, 085116 – Published 13 February 2013
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  • INTRODUCTION
  • EXPERIMENTAL TECHNIQUES
  • EXPERIMENTAL DETAILS
  • RESULTS
  • DISCUSSIONS AND SUMMARY
  • ACKNOWLEDGEMENTS
    • References

    Abstract

    We investigate electron transport across a complex oxide heterointerface of La0.67Sr0.33MnO3 (LSMO) on Nb:SrTiO3 (Nb:STO) at different temperatures. For this, we employ the conventional current-voltage method as well as the technique of ballistic electron emission microscopy (BEEM), which can probe lateral inhomogeneities in transport at the nanometer scale. From current-voltage measurements, we find that the Schottky barrier height (SBH) at the LSMO/Nb:STO interface decreases at low temperatures accompanied by a larger than unity ideality factor. This is ascribed to the tunneling dominated transport caused by the narrowing of the depletion width at the interface. However, BEEM studies of such unbiased interfaces do not exhibit SBH lowering at low temperatures, implying that this is triggered by the modification of the interface due to an applied bias and is not an intrinsic property of the interface. Interestingly, the SBH at the nanoscale, as extracted from BEEM studies, at different locations in the device is found to be spatially homogeneous and similar both at room temperature and at low temperatures. Our results highlight the application of BEEM in characterizing electron transport and its homogeneity at such unbiased complex oxide interfaces and yield insights into the origin of the temperature dependence of the SBH at biased interfaces.

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    • Received 26 December 2012

    DOI:https://doi.org/10.1103/PhysRevB.87.085116

    ©2013 American Physical Society

    Authors & Affiliations

    K. G. Rana, S. Parui, and T. Banerjee*

    • Physics of Nanodevices, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, Netherlands

    • *t.banerjee@rug.nl

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    Issue

    Vol. 87, Iss. 8 — 15 February 2013

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    Images

    • Figure 1
      Figure 1
      (a) Sketch of the I-V measurement on a LSMO/Nb:STO device. (b) The different energy levels in the metal and semiconductor are shown along with the Schottky barrier height, which is defined as the difference between the work function of LSMO and electron affinity in Nb:STO. (c) Schematic layout of the BEEM technique (not to scale). The tunnel voltage, VT, is applied between the PtIr STM tip and the LSMO film, with the tunnel current, IT, kept constant by feedback. The LSMO/Nb:STO interface is thus unbiased. (d) Energy band diagram of the BEEM technique showing the injected hot electron distribution. The electrons transmitted in the LSMO film after scattering are collected in the conduction band of the Nb:STO semiconductor.Reuse & Permissions
    • Figure 2
      Figure 2
      (a) Current-voltage I-V characteristics for the LSMO/Nb:STO Schottky diode at room temperature, at 200 K, and at 120 K. A clear rectification is observed in all cases. (b) The Schottky barrier heights and the ideality factors are extracted from (a) using Eq. (1) at different measurement temperatures.Reuse & Permissions
    • Figure 3
      Figure 3
      (a) BEEM spectra for the LSMO (13 u.c.)/Nb:STO Schottky interface at RT (red) and at 120 K (green). Each spectrum is a representative of several spectra taken at the same location. (b) The extracted SBH at the LSMO (13 u.c.)/Nb:STO Schottky interface, obtained by plotting the square root of the normalized IB with VT and fitting it to the Bell-Kaiser model at RT, and (c) the same plot at 120 K. The insets in (b) and (c) show the distribution of Schottky barrier heights obtained at different locations in the device at RT and at 120 K, respectively.Reuse & Permissions
    • Figure 4
      Figure 4
      (a) Variation of E0 (tunneling parameter) with temperature. The blue dotted line represents the fit given by Eq. (7). (b) Depletion width in Nb:STO, calculated from Eq. (8) with varying temperature. The red solid curve is at zero bias, i.e., V=0 V, whereas the blue dashed curve is at an applied bias of 0.5 V. The blue plot shows that the depletion width in Nb:STO reduces with the external applied field at all temperatures.Reuse & Permissions
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