Mobility Extraction in 2D Transition Metal Dichalcogenide Devices—Avoiding Contact Resistance Implicated Overestimation

Schottky barrier (SB) transistors operate distinctly different from conventional metal‐oxide semiconductor field‐effect transistors, in a unique way that the gate impacts the carrier injection from the metal source/drain contacts into the channel region. While it has been long recognized that this can have severe implications for device characteristics in the subthreshold region, impacts of contact gating of SB in the on‐state of the devices, which affects evaluation of intrinsic channel properties, have been yet comprehensively studied. Due to the fact that contact resistance (RC) is always gate‐dependent in a typical back‐gated device structure, the traditional approach of deriving field‐effect mobility from the maximum transconductance (gm) is in principle not correct and can even overestimate the mobility. In addition, an exhibition of two different threshold voltages for the channel and the contact region leads to another layer of complexity in determining the true carrier concentration calculated from Q = COX * (VG–VTH). Through a detailed experimental analysis, the effect of different effective oxide thicknesses, distinct SB heights, and doping‐induced reductions in the SB width are carefully evaluated to gain a better understanding of their impact on important device metrics. Mobility overestimation extracted from 2‐terminal measurement is investigated, which is attributed to impacts of contact gating of Schottky barrier in the on‐state of devices. Comprehensive analysis including impacts of effective oxide thickness of gate dielectrics, different TMD channel materials, and an involvement of extrinsic doping schemes are provided to gain a better understanding of their impacts on important device metrics.