Transition metal dichalcogenides (TMDCs) have emerged as promising channel materials for field-effect transistors (FETs) due to their atomically thin nature, tunable bandgaps, and high carrier mobility potential. Unlike conventional silicon-based FETs, TMDC-FETs offer unique advantages such as immunity to short-channel effects at reduced dimensions, making them suitable for next-generation nanoelectronics. However, several challenges must be addressed to realize their full potential, including contact engineering, dielectric integration, and mobility limitations.

Contact engineering is a critical aspect of TMDC-FET performance. The formation of Schottky barriers at the metal-TMDC interface often leads to high contact resistance, limiting current injection. Fermi-level pinning, caused by metal-induced gap states or defects at the interface, exacerbates this issue. For instance, in MoS2 FETs, the Fermi level tends to pin near the conduction band edge regardless of the metal work function, resulting in significant electron Schottky barriers. Strategies to mitigate this include using low-work-function metals like scandium or titanium, which reduce the electron injection barrier. Alternatively, phase-engineered contacts, where metallic phases of TMDCs (e.g., 1T-MoS2) are locally induced at the contact regions, have shown promise in lowering contact resistance. Another approach involves van der Waals contacts, where metals are transferred onto TMDCs without direct deposition, minimizing interface defects.

Dielectric integration is another challenge in TMDC-FETs. The absence of dangling bonds on TMDC surfaces complicates the deposition of high-quality dielectrics via conventional methods like atomic layer deposition (ALD). Poor dielectric interfaces introduce charged impurities and traps, degrading mobility and subthreshold swing. To address this, hexagonal boron nitride (hBN) is often used as a gate dielectric due to its atomically smooth surface and low trap density. However, hBN is challenging to scale for large-area applications. Alternative approaches include using high-k dielectrics like HfO2 with seed layers or organic self-assembled monolayers to improve nucleation and reduce interface traps. The choice of dielectric also impacts the gate control and leakage currents, with high-k materials offering better electrostatic control but potentially introducing more defects.

Mobility limitations in TMDC-FETs arise from various scattering mechanisms, including phonon scattering, Coulomb scattering from charged impurities, and defects within the TMDC lattice. At room temperature, phonon scattering dominates, limiting the mobility of monolayer MoS2 to around 100 cm²/Vs. Coulomb scattering can be mitigated by using substrates with low surface roughness and charge traps, such as hBN or SiO2 with rigorous cleaning. Defect engineering, such as sulfur vacancy passivation using thiol chemistry, has been shown to improve mobility by reducing trap states. Strain engineering is another strategy, where uniaxial or biaxial strain modifies the band structure, enhancing carrier transport. For example, applying tensile strain to WS2 can reduce the effective mass of electrons, leading to higher mobility.

Performance enhancement strategies extend beyond contact and dielectric optimization. Doping, both substitutional and electrostatic, can modulate carrier concentrations and improve conductivity. Substitutional doping involves replacing chalcogen or transition metal atoms with heteroatoms, such as niobium for p-type doping in MoS2. Electrostatic doping, achieved via gate biasing or charge transfer layers, offers non-destructive tuning but requires precise control. Encapsulation with hBN or other inert materials protects TMDCs from environmental degradation, preserving their electronic properties. Additionally, heterostructure engineering, where different TMDCs are stacked to form type-II band alignments, can enhance carrier separation and reduce recombination.

Comparing TMDC-FETs with silicon and other 2D material-based FETs highlights their relative strengths and weaknesses. Silicon FETs benefit from mature fabrication processes and high mobilities (up to 1400 cm²/Vs for electrons), but face limitations in scalability below 5 nm due to short-channel effects. Graphene-based FETs exhibit ultra-high mobilities (exceeding 10,000 cm²/Vs) but lack a bandgap, resulting in poor on-off ratios. TMDC-FETs bridge this gap with moderate mobilities and sizable bandgaps (1-2 eV), enabling both high on-off ratios and nanoscale operation. However, their mobility is still lower than silicon, and contact resistance remains higher than in graphene devices. Other 2D materials like black phosphorus offer higher mobilities but suffer from ambient instability, unlike the more robust TMDCs.

In summary, TMDC-FETs represent a compelling alternative to silicon and other 2D materials for future transistor technologies. Advances in contact engineering, dielectric integration, and mobility enhancement are critical to unlocking their potential. While challenges remain, the unique properties of TMDCs position them as strong candidates for post-silicon electronics, particularly in applications requiring atomic-scale thickness and tunable bandgaps. Continued research into material synthesis, interface engineering, and device architecture will be essential to overcome current limitations and achieve performance parity with established technologies.