Fig. 5: Fermi-level-modulated van der Waals (vdW) semimetal contact electrodes.
a Transfer characteristics of 2H-MoTe2 FETs with vdW Au/1T’- (red), Pt/1T’- (gold), and Ag/1T’-MoTe2 (purple) contacts. Inset illustrates threshold voltage (Vth) shifts by metallized 3D metals on vdW semimetal contacts. b, c Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) characterization of the interfaces at 1T’-MoTe2 deposited by 3D metals; Ag (purple), Au (red), and Pt (gold). Spectra of pristine 1T’-MoTe2 are displayed as gray curves. b UPS spectra of the 3D metal/1T’-MoTe2 surfaces in secondary electron edge region. Work function (WF) can be extracted at the x-intercept of linear regime (solid lines) as kinetic energy (Ek) is the difference between the energy of ultraviolet photons (~21.21 eV for the He I radiation) and binding energy (Eb). c Normalized XPS spectra of Te 3d core level acquired from the 3D metal/1T’-MoTe2 interfaces. Dotted line indicates Eb of pristine 1T’-MoTe2. d Typical Ids–Vg of 2H-MoTe2 FETs contacted with vdW Au/1T’-MoTe2 (red) and 3D Pt (blue) at various temperatures (T). Inset shows the Ion/Ioff ratio with T. e Thermionic barrier height (ΦB) values measured at various Vg for hole transfer with 3D Pt (blue), vdW Ag/1T’-MoTe2 (purple), and vdW Au/1T’-MoTe2 contacts (red) in 2H-MoTe2 FET. The Schottky barrier heights (SBHs), i.e., ΦB values at the flat band voltages (VFB), are indicated by arrows. f Comparison of SBH values of our 2H-MoTe2 FETs (colored stars) with reported ones23,34,36,60,61,62,63 (binned black) depending on WFs of different metal contacts. Fermi level pinning (FLP) factors, S (=dΦB/dWF), for vdW semimetal and 3D contacts are displayed. g, h Band structures depicting formation of SBH and alignment of Fermi level (EF) in 2H-MoTe2 FETs with (g) vdW semimetal and (h) 3D metal contact. Ec and Ev indicate energy levels of conduction and valance band edge, respectively.
