Full Energy Spectra of Interface State Densities for n‐ and p‐type MoS₂ Field‐Effect Transistors

Abstract

2D materials are promising to overcome the scaling limit of Si field-effect transistors (FETs). However, the insulator/2D channel interface severely degrades the performance of 2D FETs, and the origin of the degradation remains largely unexplored. Here, the full energy spectra of the interface state densities (D it ) are presented for both n-and p-MoS 2 FETs, based on the comprehensive and systematic studies, i.e., full rage of channel thickness and various gate stack structures with h-BN as well as high-k oxides. For n-MoS 2 , D it around the mid-gap is drastically reduced to 5 × 10 11 cm −2 eV −1 for the heterostructure FET with h-BN from 5 × 10 12 cm −2 eV −1 for the high-k top-gate. On the other hand, D it remains high, ≈10 13 cm −2 eV −1 , even for the heterostructure FET for p-MoS 2 . The systematic study elucidates that the strain induced externally through the substrate surface roughness and high-k deposition process is the origin for the interface degradation on conduction band side, while sulfur-vacancy-induced defect states dominate the interface degradation on valance band side. The present understanding of the interface properties provides the key to further improving the performance of 2D FETs.

A compact model for transition metal dichalcogenide field effect transistors with effects of interface traps

“…, which is consistent with other published data [4]. By optimizing the interface between MoS 2 channel and gate oxide, D it can be reduced and µ can be improved.…”

“…That results in a large amount of numerical calculations in previous models [7,8]. On the other hand, according to experimental results [4], Cq increases exponentially with Vgs and thus C it is negligible in the strong-inversion region. In the sub-threshold region, the sub-threshold swing (SS) is dominated by C it and Cox.…”

“…Interface traps are inevitable in TMD FETs [3,4]. However, in previously published models, they were neglected in [5,6], or a large amount of numerical calculations [7,8] were unavoidable which can introduce the convergence problem.…”

“…Figure 1(c) shows the schematic of Vgs dependences of Cox, Cq, and C it . The real C it keeps as a constant in the sub-threshold region and becomes a complex function of Vgs when the FET goes into the transition and strong-inversion regions owing to the energy distribution of the interface traps [4]. That results in a large amount of numerical calculations in previous models [7,8].…”

Understanding interface properties in 2D heterostructure FETs

“…10(b), the defects states for NbMo are formed just below the valence band maximum [71]. However, interestingly, the defect density of NbMo is smaller than that of VS, even in the Nb-doped p-type MoS2 crystal [21,72]. Moreover, it is reported that p-type conduction for the "n-type" monolayer MoS2 FET was not detected, even using the ion gating; instead, the abnormal conductance peak was observed due to the defect states of VS [73].…”