Unprecedented Hole Concentration of NiSe₂ Electrodes Leading to Hole Degeneration of Entire WSe₂ Channels

Semimetal electrodes for 2D semiconductors have been extensively studied; however, research on p-type semimetals has been limited due to the scarcity of materials that satisfy both high work functions and low resistances. In response, we investigated the behavior of NiSe₂ as an electrode. Utilizing a novel co-evaporation method that suppresses oxidation and contamination, we synthesized NiSe₂ demonstrating a high work function of 5.53 eV, a low resistance of 5.81 × 10^-5 Ω cm, and a record hole concentration exceeding 10²³ cm^-3. We confirmed that when WSe₂ comes into contact with NiSe₂, the Fermi level of WSe₂ falls below the work function of NiSe₂, leading to complete hole degeneration of the channel. This unusual Fermi level alignment correlates with the high hole concentration in NiSe₂ and the maximum energy level of its hole pockets. Our research provides new insights into how an electrode's hole concentration affects channel behavior.