Search Results (3)

2D field-effect transistors (FETs) fabricated with transition metal dichalcogenide (TMD) materials are a potential replacement for the silicon-based CMOS. However, the lack of advancement in p-type contact is also a key factor hindering TMD-based CMOS applications. The less investigated path towards improving electrical characteristics based on contact geometries with low contact resistance (R_C) has also been established. Moreover, finding contact metals to reduce the R_C is indeed one of the significant challenges in achieving the above goal. Our research provides the first comparative analysis of the three contact configurations for a WSe₂ monolayer with different noble metals (Rh, Ru, and Pd) by employing ab initio density functional theory (DFT) and non-equilibrium Green’s function (NEGF) methods. From the perspective of the contact topologies, the R_C and minimum subthreshold slope (SS_MIN) of all the conventional edge contacts are outperformed by the novel non-van der Waals (vdW) sandwich contacts. These non-vdW sandwich contacts reveal that their R_C values are below 50 Ω∙μm, attributed to the narrow Schottky barrier widths (SBWs) and low Schottky barrier heights (SBHs). Not only are the R_C values dramatically reduced by such novel contacts, but the SS_MIN values are lower than 68 mV/dec. The new proposal offers the lowest R_C and SS_MIN, irrespective of the contact metals. Further considering the metal leads, the WSe₂/Rh FETs based on the non-vdW sandwich contacts show a meager R_C value of 33 Ω∙μm and an exceptional SS_MIN of 63 mV/dec. The two calculated results present the smallest-ever values reported in our study, indicating that the non-vdW sandwich contacts with Rh leads can attain the best-case scenario. In contrast, the symmetric convex edge contacts with Pd leads cause the worst-case degradation, yielding an R_C value of 213 Ω∙μm and an SS_MIN value of 95 mV/dec. While all the WSe₂/Ru FETs exhibit medium performances, the minimal shift in the transfer curves is interestingly advantageous to the circuit operation. Conclusively, the low-R_C performances and the desirable SS_MIN values are a combination of the contact geometries and metal leads. This innovation, achieved through noble metal leads in conjunction with the novel contact configurations, paves the way for a TMD-based CMOS with ultra-low R_C and rapid switching speeds. Full article

Tungsten diselenide (${\mathrm{WSe}}_2$) has emerged as a promising ambipolar semiconductor material for field-effect transistors (FETs) due to its unique electronic properties, including a sizeable band gap, high carrier mobility, and remarkable on–off ratio. However, engineering the contacts to ${\mathrm{WSe}}_2$ remains an issue, and high contact barriers prevent the utilization of the full performance in electronic applications. Furthermore, it could be possible to tune the contacts to ${\mathrm{WSe}}_2$ for effective electron or hole injection and consequently pin the threshold voltage to either conduction or valence band. This would be the way to achieve complementary metal–oxide–semiconductor devices without doping of the channel material.This study investigates the behaviour of two-dimensional ${\mathrm{WSe}}_2$ field-effect transistors with multi-layer palladium diselenide (${\mathrm{PdSe}}_2$) as a contact material. We demonstrate that ${\mathrm{PdSe}}_2$ contacts favour hole injection while preserving the ambipolar nature of the channel material. This consequently yields high-performance p-type ${\mathrm{WSe}}_2$ devices with ${\mathrm{PdSe}}_2$ van der Waals contacts. Further, we explore the tunability of the contact interface by selective laser alteration of the ${\mathrm{WSe}}_2$ under the contacts, enabling pinning of the threshold voltage to the valence band of ${\mathrm{WSe}}_2$, yielding pure p-type operation of the devices. Full article

The monitoring of ethylene is of great importance to fruit and vegetable quality, yet routine techniques rely on manual and complex operation. Herein, a chemiresistive ethylene sensor based on reduced graphene oxide (rGO)/tungsten diselenide (WSe₂)/Pd heterojunctions was designed for room-temperature (RT) ethylene detection. The sensor exhibited high sensitivity and quick p-type response/recovery (33/13 s) to 10–100 ppm ethylene at RT, and full reversibility and excellent selectivity to ethylene were also achieved. Such excellent ethylene sensing behaviors could be attributed to the synergistic effects of ethylene adsorption abilities derived from the negative adsorption energy and the promoted electron transfer across the WSe₂/Pd and rGO/WSe₂ interfaces through band energy alignment. Furthermore, its application feasibility to banana ripeness detection was verified by comparison with routine technique through simulation experiments. This work provides a feasible methodology toward designing and fabricating RT ethylene sensors, and may greatly push forward the development of modernized intelligent agriculture. Full article