Effect of oxygen and ozone on p-type doping of ultra-thin WSe2 and MoSe2 field effect transistors.

We report on the p-type doping effect of oxygen and ozone molecules on mono- and few-layer WSe2 and MoSe2 field effect transistors. We show that adsorption of oxygen and ozone under ambient conditions results in subtantial doping and corresponding enhancement in the hole conductivity of the devices. Ozone-induced doping is found to be rapid and efficient, saturating within minutes of exposure whereas oxygen-induced doping occurs over a period of days to reach the equivalent level of doping. Our observations reveal that the water adlayer on the material surface plays a crucial role in solubilizing oxygen and ozone and in forming a redox couple with a large chemical potential.