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P-type electrical contacts for two-dimensional transition metal dichalcogenides

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Digital logic circuits are based on complementary pairs of n- and p-type field effect transistors (FETs) via complementary metal oxide semiconductor (CMOS) technology. In three dimensional (3D or bulk) semiconductors, substitutional doping of acceptor or donor impurities is used to achieve p- and n-type FETs. However, the controllable p-type doping of low-dimensional semiconductors such as two-dimensional transition metal dichalcogenides (2D TMDs) has proved to be challenging. Although it is possible to achieve high quality, low resistance n-type van der Waals (vdW) contacts on 2D TMDs1–5, obtaining p-type devices from evaporating high work function metals onto 2D TMDs has not been realised so far. Here we report high-performance p-type devices on single and few-layered molybdenum disulphide (MoS2) and tungsten diselenide (WSe2) based on industry-compatible electron beam evaporation of high work function metals such as Pd and Pt. Using atomic resolution imaging and spectroscopy, we demonstrate near ideal vdW interfaces without chemical interactions between the 2D TMDs and 3D metals. Electronic transport measurements reveal that the Fermi level is unpinned and p-type FETs based on vdW contacts exhibit low contact resistance of 3.3 kΩ·μm, high mobility values of ~ 190 cm2-V-1s-1 at room temperature with saturation currents in excess of > 10-5 Amperes per micron (A-m-1) and on/off ratio of 107. We also demonstrate an ultra-thin photovoltaic cell based on n- and p-type vdW contacts with an open circuit voltage of 0.6 V and power conversion efficiency of 0.82%.



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Nature Research
European Commission Horizon 2020 (H2020) ERC (101019828)
EPSRC (EP/T026200/1)
Royal Society (NIF/R1/180138)
Royal Society (WRM\FT\180009)
ERC Adv Grant