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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]

Ultra-thin MoS2 film doping through surface functionalization with physically adsorbed species is of great interest due to its ability to dope the film without reduction in the carrier mobility. However, there is a need for understanding how the thickness of the MoS2 film is related to the induced surface doping for improved electrical performance. In this work, we report on the relation of MoS2 film thickness with the doping effect induced by the n-dopant adsorbate poly(vinyl-alcohol). Field effect transistors built using MoS2 films of different thicknesses were electrically characterized, and it was observed that the ION/OFF ratio after doping in thin films is more than four orders of magnitudes greater when compared with thick films. Additionally, a semi-classical model tuned with the experimental devices was used to understand the spatial distribution of charge in the channel and explain the observed behavior. From the simulation results, it was revealed that the two-dimensional carrier density induced by the adsorbate is distributed rather uniformly along the complete channel for thin films (<5.2 nm) contrary to what happens for thicker films. [ABSTRACT FROM AUTHOR]

The effects of oxidants both in the channel and contact regions of MoS2 transistors are discussed through a systematic experimental study. This letter highlights the issues of partial instability in metal-organic chemical vapor deposition MoS2 and proposes a procedure, which considerably improves the electrical characteristics of back-gated transistors. By avoiding ambient exposure and layer oxidation, contact resistance can be reduced and intrinsic mobility increased by 50%. [ABSTRACT FROM AUTHOR]

A novel method for fast and flexible fin field effect transistor (FinFET) prototyping using a Ga+ focused ion beam is presented. The fin width and height control is explored, aiming for the successful fabrication of prototypes. This method results in fins with negligible Ga incorporation, when compared to traditional focused ion beam milling techniques. Our method for multiple fin FinFET prototyping enables advanced device fabrication and great flexibility regarding both the number of fins and fin width. Working FinFET prototypes have been fabricated using the proposed fin definition method, and the electrical characterization is discussed. [ABSTRACT FROM AUTHOR]

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.

For the integration of two-dimensional (2D) transition metal dichalcogenides (TMDC) with high-performance electronic systems, one of the greatest challenges is the realization of doping and comprehension of its mechanisms. Low-temperature atomic layer deposition of aluminum oxide is found to n-dope MoS 2 and ReS 2 but not WS 2 . Based on electrical, optical, and chemical analyses, we propose and validate a hypothesis to explain the doping mechanism. Doping is ascribed to donor states in the band gap of Al x O y , which donate electrons or not, based on the alignment of the electronic bands of the 2D TMDC. Through systematic experimental characterization, incorporation of impurities (e.g., carbon) is identified as the likely cause of such states. By modulating the carbon concentration in the capping oxide, doping can be controlled. Through systematic and comprehensive experimental analysis, this study correlates, for the first time, 2D TMDC doping to the carbon incorporation on dielectric encapsulation layers. We highlight the possibility to engineer dopant layers to control the material selectivity and doping concentration in 2D TMDC.