Doping-Induced Dipole Effects for Barrier-Free P-Type MoS₂–Metal Contacts

This study investigated the effect of substitutional doping on the electrostatics and contact resistance of MoS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>−metal Schottky contacts through first-principles simulations. The introduction of dopants induced interface dipole charges, significantly reducing the Schottky barrier height (φ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub>). As a representative example, Nb doping in MoS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> effectively lowered the p-type Schottky barriers. The delta-function approximation was employed to model the dipole charge and determine the physical relationship between the doping concentration (N<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub>) and φ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> reduction in monolayer-and multilayer-doped MoS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>−metal contacts. Simulations based on this model and the Schottky theory revealed that dipole-induced barrier lowering can reduce contact resistance by several orders of magnitude, achieving values as low as 24 Ω∙μm for a p-type MoS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>−metal contact with a N<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> of 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> and an intrinsic φ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> of 0.1 eV. These findings highlight doping as a transformative approach for achieving low-resistance Ohmic contacts for high-performance two-dimensional field-effect transistors.