Stacked Janus Device Concepts: Abrupt pn-Junctions and Cross-Plane Channels

Abstract

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Van der Waals Contact to 2D Semiconductors with a Switchable Electric Dipole: Achieving Both n‐ and p‐Type Ohmic Contacts to Metals with a Wide Range of Work Functions

“…The calculated metal–semiconductor separation and binding energies (of 0.26–0.46 J m −2 , Table S3, Supporting Information) suggest that the interaction of pS and Mo 2 CT 2 is van der Walls type, which favor weak Fermi‐level pinning44 and hence the contact type could be effectively tuned by switching the built‐in dipole of pS. This is why our current work constrained to 2D metals because bulk 3D metals could have a stronger Fermi‐level pinning55 and 3D metals may completely screen the cross‐plane dipole of pS 54. These effects from 3D bulk metal may make the SB‐free contact a bit difficult to achieve in 3D metal‐pS junctions.…”

“…Due to the lattice mismatch between pS and Mo 2 CT 2 , special care is needed to build an MpSJ model to obtain a small in‐plane lattice mismatch. As the semiconductor energy gap is sensitive to strain, the lattice constant of pS is fixed and that of Mo 2 CT 2 is adjusted to compensate the lattice misfit, since the metal Fermi level is less sensitive to strain 52–54. The 72 lattice models of MpSJs, including lattice constant, supercell, and magnitude of strain, for pS on Mo 2 CT 2 are listed in Tables S1 and S2, Supporting Information.…”

“…We can neglect it while still give a rather good explanation to the origin of contact‐type transition since the metal–semiconductor interaction has two effects on the band gap of pS that canceled out each other. One effect is the vdW interaction of metal to a semiconductor, which usually reduces the band gap; the other effect is unique to pS, that the metal screen the intrinsic dipole in pS and increase the band gap 54…”

“…One effect is the vdW interaction of metal to a semiconductor, which usually reduces the band gap; the other effect is unique to pS, that the metal screen the intrinsic dipole in pS and increase the band gap. [54] The total potential step (ΔV tot in Figure 3c,d) in MpSJ effectively regulates the SBH. The work-function of metal on the pS side in MpSJ depends on the intrinsic dipole of pS and the interface dipole resulted from the charge redistribution at 2D metal-pS interface.…”

“…This is why our current work constrained to 2D metals because bulk 3D metals could have a stronger Fermilevel pinning [55] and 3D metals may completely screen the cross-plane dipole of pS. [54] These effects from 3D bulk metal may make the SB-free contact a bit difficult to achieve in 3D metal-pS junctions. Due to extremely low/high WF of Mo 2 C(OH) 2 /Mo 2 CO 2 relative to CBM/VBM of pS in both the (001) and (00-1) contact (Figure 2), SB-free n-type contact is formed in Mo 2 C(OH) 2 -pS junctions and SB-free p-type contact is formed in Mo 2 CO 2 -pS junctions, which are similar to that in MSJ with traditional semiconductors without an intrinsic dipole contacting to 2D metals with extremely low/high WF.…”