Unprecedented Hole Concentration of NiSe<sub>2</sub> Electrodes Leading to Hole Degeneration of Entire WSe<sub>2</sub> Channels.

Bae, Ji Kwon; Ghods, Soheil; Cho, Hyeon Ho; Jang, Hochan; Kim, Seung-Il; Lee, Jae-Hyun; Yu, Hak Ki · Nano Lett · 2024

basic_science · Level V

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Abstract

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 NiSe<sub>2</sub> as an electrode. Utilizing a novel co-evaporation method that suppresses oxidation and contamination, we synthesized NiSe<sub>2</sub> demonstrating a high work function of 5.53 eV, a low resistance of 5.81 × 10<sup>-5</sup> Ω cm, and a record hole concentration exceeding 10<sup>23</sup> cm<sup>-3</sup>. We confirmed that when WSe<sub>2</sub> comes into contact with NiSe<sub>2</sub>, the Fermi level of WSe<sub>2</sub> falls below the work function of NiSe<sub>2</sub>, leading to complete hole degeneration of the channel. This unusual Fermi level alignment correlates with the high hole concentration in NiSe<sub>2</sub> and the maximum energy level of its hole pockets. Our research provides new insights into how an electrode's hole concentration affects channel behavior.