van der Waals Stacking Induced Transition from Schottky to Ohmic Contacts: 2D Metals on Multilayer InSe

Abstract

Incorporation of two-dimensional (2D) materials in electronic devices inevitably involves contact with metals, and the nature of this contact (Ohmic and/or Schottky) can dramatically affect the electronic properties of the assembly. Controlling these properties to reliably form low-resistance Ohmic contact remains a great challenge due to the strong Fermi level pinning (FLP) effect at the interface. Herein, we employ density functional theory calculations to show that van der Waals stacking can significantly modulate Schottky barrier heights in the contact formed between multilayer InSe and 2D metals by suppressing the FLP effect. Importantly, the increase of InSe layer number induces a transition from Schottky to Ohmic contact, which is attributed to the decrease of the conduction band minimum and rise of the valence band maximum of InSe. Based on the computed tunneling and Schottky barriers, Cd 3 C 2 is the most compatible electrode for 2D InSe among the materials studied. This work illustrates a straightforward method for developing more effective InSe-based 2D electronic nanodevices.

Tunable Electronic Properties and Potential Applications of 2D GeP/Graphene van der Waals Heterostructure

“…The vdW‐DF functional method with exchange term proposed by Klimes et al was employed for all simulations to describe the van der Waals (vdW) interactions 40. The calculated vertical distance, binding energy, and effective potential are in good agreement with previous reports 41. The interaction between valence electrons and the atomic core is computed within the standard norm‐conserving Troullier–Martins pseudopotential 42.…”

“…The calculated value of E b is −31.42 meV Å −2 (equivalent to 0.50 J m −2 ) for the GeP/Gr heterostructure, which is smaller than the typical vdW force value of about ‐20 meV Å −2 that reported previously by DFT calculations,48 suggesting the superior stability of the GeP/Gr heterostructure for practical applications. The above E b value of the GeP/Gr heterostructure is also smaller than that of the blue phosphorus/Gr (approximately −21 meV Å −2 ),45 C 3 N/Gr heterostructure (about −23 meV Å −2 ),49 InSe/Gr heterostructure 41. More importantly, taken the exfoliation energy of bulk GeP (0.33 J m −2 ) into account,15 the formation of the GeP/Gr heterostructure is anticipated to be experimentally achievable.…”

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

“…Most importantly, bilayer pS contacting to medium‐WF Mo 2 CF 2 can form both n‐ and p‐type SB‐free contacts using the same pS by switching its built‐in electric dipole, and, metallic Mo 2 CF 2 partially screen the cross‐plane dipole in pS resulting in tunable bandgap. Our findings for MpSJ, that is, both n‐ and p‐type SB‐free contacts can be obtained with the same pS contacting to metals with a wide range of work‐functions (which is not limited to extremely low or high metal work‐function as reported in literature),40,46 are essential for high‐performance optoelectronic devices49 and complementary metal‐oxide‐semiconductor (CMOS) logic circuitry 50…”

“…The potential of 2D pS in electronics, however, is yet to be fully explored. The current work explores the potential of 2D pS in metal–semiconductor junctions (MSJ), which plays an important role in low‐power electronics, straintronics, flextronics, piezotronics, optoelectronics, valleytronics, neurotronics, and energy harvesting devices 39–42. A recent work studied blue‐phosphorene‐phase of GeSe with an intrinsic dipole contacts to semimetal graphene 43.…”

“…Particularly, p‐type contacts are relatively difficult to achieve 39,45. SBH becomes tunable and can even vanish in MSJs with 2D metals 40,46–48. However, extremely low or high work‐function is needed for the 2D metal to obtain vanishing SBH.…”