Low Resistance Ohmic Contact to P-type Monolayer WSe2

Advanced microelectronics in the future may require semiconducting channel materials beyond silicon. Two-dimensional (2D) semiconductors, characterized by their atomically thin thickness, hold immense promise for high-performance electronic devices at the nanometer scale with lower heat dissipation. One challenge for achieving high-performance 2D semiconductor field effect transistors (FET), especially for p-type materials, is the high electrical contact resistance present at the metal-semiconductor interface. In conventional bulk semiconductors, low resistance ohmic contact is realized through heavy substitutional doping with acceptor or donor impurities at the contact region. The strategy of substitutional doping, however, does not work for p-type 2D semiconductors such as monolayer tungsten diselenide (WSe$_2$).In this study, we developed highly efficient charge-transfer doping with WSe$_2$/$\alpha$-RuCl$_3$ heterostructures to achieve low-resistance ohmic contact for p-type WSe$_2$ transistors. We show that a hole doping as high as 3$\times$10$^{13}$ cm$^{-2}$ can be achieved in the WSe$_2/\alpha$-RuCl$_3$ heterostructure due to its type-III band alignment. It results in an Ohmic contact with resistance lower than 4 k Ohm $\mu$m at the p-type monolayer WSe$_2$/metal junction. at room temperature. Using this low-resistance contact, we demonstrate high-performance p-type WSe$_2$ transistors with a saturation current of 35 $\mu$A$\cdot$ $\mu$m$^{-1}$ and an I$_{ON}$/I$_{OFF}$ ratio exceeding 10$^9$ It could enable future microelectronic devices based on 2D semiconductors and contribute to the extension of Moore's law.