Catalytic effect of nano-thick gold electrodes on p-doping of diselenides during annealing process

Two-dimensional transition metal dichalcogenides (TMDs) show great promise for developing the next generation of electronic and optoelectronic devices. However, most TMDs have n-type or n-dominant bipolar characteristics, and this severely limits their potential for being designed as multi-functional heterostructures. Recently, thermal annealing has been reported as an easy means of p-doping TMDs, but the mechanism remains ambiguous, thereby preventing reliable outcomes and it becoming a mature doping technology for TMDs. Here, the mechanism of thermal annealing for p-doping a 2D selenide is investigated thoroughly, revealing the key role of the catalytic effect of nano-thick gold electrodes in achieving p-doping. As an example, 2D SnSe2 with a fairly high electron density of ∼1018 cm−3 is used, and its electrical performance is greatly enhanced after thermal annealing when 30-nm-thick gold electrodes are deposited. The results of performing XPS and Auger electron spectroscopy on samples before and after annealing show that the p-doping effect is due to the oxidation of selenide atoms, during which the gold acts as a critical catalytic element. This method is also shown to be valid for other 2D selenides including WSe2 and MoSe2, and the present findings offer new avenues for enriching the electrical properties of 2D selenides by means of annealing.