Universal low-temperature Ohmic contacts for quantum transport in transition metal dichalcogenides

Low carrier mobility and high electrical contact resistance are two major obstacles prohibiting explorations of quantum transport in TMDCs. Here, we demonstrate an effective method to establish low-temperature Ohmic contacts in boron nitride encapsulated TMDC devices based on selective etching and conventional electron-beam evaporation of metal electrodes. This method works for most extensively studied TMDCs in recent years, including MoS2, MoSe2, WSe2, WS2, and 2H-MoTe2. Low electrical contact resistance is achieved at 2 K. All of the few-layerTMDCdevices studied show excellent performance with remarkably improved field-effect mobilities ranging from 2300 to 16 000 cm 2 V-1 s(-1), as verified by the high carrier mobilities extracted from Hall effect measurements. Moreover, both high-mobility n-type and p-typeTMDCchannels can be realized by simply using appropriate contact metals. Prominent Shubnikov-de Haas oscillations have been observed and investigated in these high-quality TMDC devices.