Efficient Ohmic Contact in Monolayer CrX₂N₄ (X = C, Si) Based Field‐Effect Transistors

Abstract

Developing Ohmic contact systems or achieving low contact resistance is significant for high‐performance semiconductor devices. This work comprehensively investigates the interfacial properties of CrX2N4 (X = C, Si) based field‐effect transistors (FETs) with different metal (Ag, Au, Cu, Ni, Pd, Pt, Ti, and graphene) electrodes by using electronic structure calculations and quantum transport simulations. It is highlighted that the stronger interlayer coupling allows CrC2N4 to form an n‐type Ohmic contact with Ti electrode in the vertical direction. Furthermore, the absence of tunneling barrier at the CrC2N4–Ti interface greatly improves the electron injection efficiency. On the other hand, the studied metals form Schottky contact with CrC2N4 at the lateral interface due to Fermi level pinning (FLP) effects. Surprisingly, the strong FLP effects restrict the Schottky barrier heights of CrSi2N4‐metal contacts to a narrow range. Where Ag, Au, Ni, Pd, Pt, Ti electrodes and Ag, Ti electrodes form ideal ohmic contact with CrSi2N4 in the vertical and lateral directions, respectively, while the other metals form quasi‐ohmic contact. Ti exhibits the highest contact performance as the electrode in both CrC2N4 and CrSi2N4 based FETs. The findings may provide fundamental understanding for designing high‐performance and energy‐efficient FETs based on CrX2N4.

First-Principles Investigation of MXene/MoSi2N4 van der Waals Heterostructures: Strong Fermi Level Pinning Effect Resulting in Ohmic Contact with Low Contact Resistance

“…In addition to SBH, tunneling possibility ( P TB ) is an important factor in measuring the device performance for carrier injection efficiency at the M/S interface, which can be calculated using the barrier width ( W B ) and barrier height ( H B ) from the plane-average electrostatic potential. ,, We simplify the irregular calculated barriers into square barriers. P TB is defined as P TB = exp ( − 2 2 m H B ℏ × W B ) where m and ℏ are the mass of free electron and reduced Planck’s constant.…”

Hydrogen-bonding enables two-dimensional metal/semiconductor tunable contacts approaching the quantum limit and the modified Schottky–Mott limit simultaneously

“…Sc and Ti can be in close contact with MoGe 2 N 4 with negligible gaps, which is consistent with previous studies. 20,21 Normally this strong chemical interaction disrupts the intrinsic electronic structure of the semiconductor, generating MIGS and leading to a strong FLP. Remarkably, the hydrogen-bonds in Ti 3 C 2 (OH) 2 /MoGe 2 N 4 belong to a moderate chemisorption that combines a small contact gap and a clean interface.…”

“…The larger work function difference between the metal and semiconductor leads to a larger Δ V , which is one of the main reasons for the deviation of the obtained Schottky barrier from the original Schottky–Mott rule for M/S contact. 21,23,39 Considering the interface dipole, the Schottky–Mott rule can be modified to the following equation: 40,53 ϕ n = W m − χ + Δ V and ϕ p = IE − W m − Δ V where ϕ n and ϕ p are the electron and hole Schottky barrier, respectively. χ and IE are the electron affinity and ionization energy of the semiconductor, respectively.…”

“…The tunneling-specific resistivity ( ρ T ) is estimated by using Simmon's model 50,51 as follows:where α = 1 under an ideal rectangular potential barrier. If , the above equation yields non-physical results, so the low-bias ( V → 0) approximation is used to calculate ρ T in this case, as follows: 20,21 …”

“…Especially for attractive future-oriented materials, such as transition metal carbides (MXenes), 15 transition metal nitrides (TMNs), 16,17 2D binary III-VI/IV-VI compounds 18 etc., achieving ideal contacts remains a critical pending challenge. [19][20][21][22] In this work, metallic functionalized MXenes are demonstrated to form ultra-clean and close hydrogen-bonding contacts with various 2D semiconductor monolayers based on first-principles. Although many theoretical [23][24][25][26][27] and experimental studies [28][29][30][31][32] have shown that MXenes can form good electrical contacts with various semiconductors due to their good conductivity and work function matching, the reported results are still limited to the range of weak vdW contacts with non-negligible tunnelling resistance.…”