Impact of contact resistance on the electrical properties of MoS₂ transistors at practical operating temperatures

Molybdenum disulphide (MoS₂) is currently regarded as a promising material for the next generation of electronic and optoelectronic devices. However, several issues need to be addressed to fully exploit its potential for field effect transistor (FET) applications. In this context, the contact resistance, R_C, associated with the Schottky barrier between source/drain metals and MoS₂ currently represents one of the main limiting factors for suitable device performance. Furthermore, to gain a deeper understanding of MoS₂ FETs under practical operating conditions, it is necessary to investigate the temperature dependence of the main electrical parameters, such as the field effect mobility (μ) and the threshold voltage (V_th). This paper reports a detailed electrical characterization of back-gated multilayer MoS₂ transistors with Ni source/drain contacts at temperatures from T = 298 to 373 K, i.e., the expected range for transistor operation in circuits/systems, considering heating effects due to inefficient power dissipation. From the analysis of the transfer characteristics (I_D-V_G) in the subthreshold regime, the Schottky barrier height (Φ_B ≈ 0.18 eV) associated with the Ni/MoS₂ contact was evaluated. The resulting contact resistance in the on-state (electron accumulation in the channel) was also determined and it was found to increase with T as R_C proportional to T^3.1. The contribution of R_C to the extraction of μ and V_th was evaluated, showing a more than 10% underestimation of μ when the effect of R_C is neglected, whereas the effect on V_th is less significant. The temperature dependence of μ and V_th was also investigated. A decrease of μ proportional to 1/T^α with α = 1.4 ± 0.3 was found, indicating scattering by optical phonons as the main limiting mechanism for mobility above room temperature. The value of V_th showed a large negative shift (about 6 V) increasing the temperature from 298 to 373 K, which was explained in terms of electron trapping at MoS₂/SiO₂ interface states.