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2D materials offer a pathway for further scaling of CMOS technology. However, for this to become a reality, both n-MOS and p-MOS should be realized, ideally with the same (standard) material. In the specific case of MoS2 field effect transistors (FETs), ambipolar transport is seldom reported, primarily due to the phenomenon of Fermi level pinning (FLP). In this study we identify the possible sources of FLP in MoS2 FETs and resolve them individually. A novel contact transfer technique is used to transfer contacts on top of MoS2 flake devices that results in a significant increase in the hole branch of the transfer characteristics as compared to conventionally fabricated contacts. We hypothesize that the pinning not only comes from the contact-MoS2 interface, but also from the MoS2-substrate interface. We confirm this by shifting to an hBN substrate which leads to a 10 fold increase in the hole current compared to the SiO2 substrate. Furthermore, we analyse MoS2 FETs of different channel thickness on three different substrates, SiO2, hBN and Al2O3, by correlating the p-branch ION/IOFF to the position of oxide defect band in these substrates. FLP from the oxide is reduced in the case of Al2O3 which enables us to observe ambipolar transport in a bilayer MoS2 FET. These results highlight that MoS2 is indeed an ambipolar material, and the absence of ambipolar transport in MoS2 FETs is strongly correlated to its dielectric environment and processing conditions. [ABSTRACT FROM AUTHOR]

Defect characterization of 2D materials is a critical aspect for their successful integration in future electronic devices. Here, a simple characterization technique is proposed that opens a path for fast, non‐invasive, quality assessment of transition metal dichalcogenide layers, such as MoS2, and their interfaces. It relates to the correlation between substrate‐induced traps and the indirect‐to‐direct photoluminescence peak ratio. It is shown that the indirect peak is quenched when interfacial trap sites are present. A physical mechanism is proposed to explain the observations based on different recombination mechanisms. [ABSTRACT FROM AUTHOR]

Implementing two-dimensional materials in field-effect transistors (FETs) offers the opportunity to continue the scaling trend in the complementary metal-oxide-semiconductor technology roadmap. Presently, the search for electrically active defects, in terms of both their density of energy states and their spatial distribution, has turned out to be of paramount importance in synthetic transition metal dichalcogenides layers, as they are suspected of severely inhibiting these devices from achieving their highest performance. Although advanced microscopy tools have allowed the direct detection of physical defects such as grain boundaries and point defects, their implementation at the device scale to assess the active defect distribution and their impact on field-induced channel charge modulation and current transport is strictly restrained. Therefore, it becomes critical to directly probe the gate modulation effect on the carrier population at the nanoscale of an FET channel, with the objective to establish a direct correlation with the device characteristics. Here, we have investigated the active channel in a monolayer MoS 2 FET through in situ scanning probe microscopy, namely, Kelvin probe force microscopy and scanning capacitance microscopy, to directly identify active defect sites and to improve our understanding of the contribution of grain boundaries, bilayer islands, and defective grain domains to channel conductance.

2D materials offer a pathway for further scaling of CMOS technology. However, for this to become a reality, both n-MOS and p-MOS should be realized, ideally with the same (standard) material. In the specific case of MoS 2 field effect transistors (FETs), ambipolar transport is seldom reported, primarily due to the phenomenon of Fermi level pinning (FLP). In this study we identify the possible sources of FLP in MoS 2 FETs and resolve them individually. A novel contact transfer technique is used to transfer contacts on top of MoS 2 flake devices that results in a significant increase in the hole branch of the transfer characteristics as compared to conventionally fabricated contacts. We hypothesize that the pinning not only comes from the contact-MoS 2 interface, but also from the MoS 2 -substrate interface. We confirm this by shifting to an hBN substrate which leads to a 10 fold increase in the hole current compared to the SiO 2 substrate. Furthermore, we analyse MoS 2 FETs of different channel thickness on three different substrates, SiO 2 , hBN and Al 2 O 3 , by correlating the p-branch I ON /I OFF to the position of oxide defect band in these substrates. FLP from the oxide is reduced in the case of Al 2 O 3 which enables us to observe ambipolar transport in a bilayer MoS 2 FET. These results highlight that MoS 2 is indeed an ambipolar material, and the absence of ambipolar transport in MoS 2 FETs is strongly correlated to its dielectric environment and processing conditions.