Controlled synthesis of van der Waals CoS2 for 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 contact induced by Fermi-level pinning is hardly removed. Herein, we prepare vdW 1T-CoS2 nanosheet as the contact electrode of WSe2 field-effect transistor (FET), which shows a considerably high on/off ratio > 107 and hole mobility of ~114.5 cm2V-1s-1. The CoS2 nanosheets exhibit metallic conductivity with thickness dependence, which surpasses most 2D transition metal dichalcogenide (TMD) metals or semimetals. The excellent FET performance of the CoS2-contacted WSe2 FET device can be attributed to the high work function of CoS2, which lowers the Schottky hole barrier. Our work provides an effective method to grow vdW CoS2 and opens up more possibilities for the application of 2D p-type semiconductors in electronic devices.