Two-dimensional metallic alloy contacts with composition-tunable work functions

Heterostructures made using two-dimensional semiconducting transition metal dichalcogenides could be used to build next-generation electronic devices. However, their performance is limited by low-quality metal–semiconductor contacts, and it remains challenging to create contacts with variable work functions using metals or metallic transition metal dichalcogenides. Here we show that a one-step chemical vapour deposition method can be used to fabricate nanoplates of a two-dimensional metallic alloy VS 2 x Se 2(1– x ) (where 0 ≤ x ≤ 1), which has a continuously tunable band alignment. The work function of the alloy can vary from 4.79 ± 0.01 eV (VSe 2 , x = 0) to 4.64 ± 0.01 eV (VS 2 , x = 1.00). The van der Waals heterostructures of VS 2 x Se 2(1– x ) and p-type tungsten diselenide (WSe 2 ) exhibit increased contact potential difference as x varies from 0 to 1, with transistors made using VSe 2 /WSe 2 contacts showing a lower potential difference and better device performance than transistors with VSSe/WSe 2 contacts, and in both cases, achieve better performance than devices with evaporated metal contacts. The contact potential difference in heterostructures of the alloy and n-type molybdenum disulfide can be turned from −71.5 mV (VSe 2 ) to 0 mV (VSSe) to 59.3 mV (VS 2 )—that is, from Schottky to ohmic contacts—with the lowest-work-function (VS 2 ) transistors showing the best performance.