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Enhanced transport in transistor by tuning transition-metal oxide electronic states interfaced with diamond

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Science Advances  28 Sep 2018:
Vol. 4, no. 9, eaau0480
DOI: 10.1126/sciadv.aau0480
  • Fig. 1 Schematic structure of diamond:H surface undergoing different ALD processes and their resulting interface electronic properties with diamond:H/MoO3 versus diamond:H/HyMoO3−x transistors.

    (A) Application of a typical MoO3 ALD process on diamond:H, resulting in surface termination degradation. (B and C) Modified ALD process of MoO3 and HyMoO3−x for preserving diamond:H termination. Right side from top to bottom: Schematic cross-sectional diagram with interface atomistic representations of diamond:H/MoO3 (top) and diamond:H/HyMoO3−x (bottom) FETs and their respective electronic band energy structures with different oxidation state ratios. CB, conduction band; VB, valence band.

  • Fig. 2 XPS of ALD-grown MoO3 and HyMoO3−x films.

    (A) Deconvolution of Mo 3d core-level spectra of Mo oxidation states Mo6+, Mo5+, and Mo4+ for MoO3 and HyMoO3−x ALD grown with different precursor ratios. (B) Deconvolution of O 1s core-level spectra of O states Mo–O and Mo–OH for MoO3 and HyMoO3−x ALD grown with different precursor ratios. (C) Dependence of Mo 3d oxidation states and O 1s states for Mo–O and Mo–OH percentages on the flux ratio of C12H30MoN4 to H2O. (D) AFM 3D view of 1 μm × 1 μm area of diamond:H/HyMoO3−x (the input flux ratio of C12H30MoN4 to H2O is 6.2 for AFM sample). A.U., arbitrary units.

  • Fig. 3 Electrical and surface characterizations before and after process fabrication.

    (A) Hall effect sheet concentration and (B) hole mobility of diamond:H/H2.3MoO2.5 versus diamond:H/MoO3 STD structures versus RTA effect (600°C). (C) XPS Mo 3d core-level spectra measurements of diamond:H/H2.3MoO2.5 and diamond:H/MoO3 before and after 6-min RTA. Mo oxidation state ratios of Mo6+, Mo5+, and Mo4+ are noted. UPS spectra of the Mo oxide synthesized layers showing (D) near Fermi edge region valence band and (E and F) secondary cutoff region, right after their synthesis (MoO3 and HyMoO3), and following their respective optimized process fabrication conditions (MoO3−x and HyMoO3−x).

  • Fig. 4 Comparison of FET characteristics.

    Comparison of diamond:H/H2.3MoO2.5 (A to C) and diamond:H/MoO3 (D to F) FET characteristics with the same dimensions: 24-μm gate length, 40-μm gate width, and 15-μm source/drain-to-gate separation: (A versus D) output characteristics, (B versus E) subthreshold characteristics, and (C versus F) transconductance and transfer characteristics (note the different scales).

  • Fig. 5 Transmission line model and key metric values for both transistors.

    (A) Left: I-V curves as measured from TLM test structures with distances (D = 10 to 45 μm) on diamond:H/MoO3 (black lines) and diamond:H/HyMoO3−x (red lines) samples (right). Linear fitting curves of corresponding sample TLM pattern. Rc and Rsh stand for contact and sheet resistance, respectively. The test structures are integrated with the FETs and have undergone the entire FET fabrication process. Distance values are actual measurements obtained from scanning electron microscopy (SEM). (B) Comparison of key figures of merit in diamond:H/MoO3 and diamond:H/H2.3MoO2.5 FET devices after full process fabrication and Hall bar structures before process fabrication.

  • Fig. 6 Band energy diagram comparison of the different cross-section heterostructure cases.

    Band energy diagram of the cross-section heterostructure for the different interface configurations following their stoichiometric situation: (A) diamond:H/MoO3 pre-processed structure, (B) diamond:H/MoO3−x/Ti-Au, and (C) diamond:H/HyMoO3−x/Ti-Au after device process fabrication.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/9/eaau0480/DC1

    Surface characterization

    FET fabrication

    FET interface structure

    Fig. S1. AFM characterization on 10 μm × 10 μm areal top surface of diamond:H/H2.3MoO2.5.

    Fig. S2. XRD pattern obtained for the ALD thin film on diamond:H substrate.

    Fig. S3. Fabrication procedure of diamond:H/HyMoO3−x MOSFET.

    Fig. S4. Cross-section SEM of a diamond:H/HyMoO3 (10 nm)/Ti-Au (10 to 100 nm) prepared sample.

  • Supplementary Materials

    This PDF file includes:

    • Surface characterization
    • FET fabrication
    • FET interface structure
    • Fig. S1. AFM characterization on 10 μm × 10 μm areal top surface of diamond:H/H2.3MoO2.5.
    • Fig. S2. XRD pattern obtained for the ALD thin film on diamond:H substrate.
    • Fig. S3. Fabrication procedure of diamond:H/HyMoO3−x MOSFET.
    • Fig. S4. Cross-section SEM of a diamond:H/HyMoO3 (10 nm)/Ti-Au (10 to 100 nm) prepared sample.

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