Controlled synthesis of van der Waals CoSfor improved p-type transistor contact.

Two-dimensional (2D) van der Waals (vdW) p-type semiconductors have shown attractive application prospects as atomically thin channels in electronic devices. However, the high Schottky hole barrier of p-type semiconductor-metal contacts induced by Fermi-level pinning is hardly removed. Herein, we prepare a vdW 1T-CoSnanosheet as the contact electrode of a WSefield-effect transistor (FET), which shows a considerably high on/off ratio > 10and a hole mobility of ∼114.5 cmVs. The CoSnanosheets exhibit metallic conductivity with thickness dependence, which surpasses most 2D transition metal dichalcogenide metals or semimetals. The excellent FET performance of the CoS-contacted WSeFET device can be attributed to the high work function of CoS, which lowers the Schottky hole barrier. Our work provides an effective method for growing vdW CoSand opens up more possibilities for the application of 2D p-type semiconductors in electronic devices.