Density functional theory based study of chlorine doped WS2-metal interface

Abstract

Investigation of a TMD-metal interface is essential for the effective functioning of monolayer TMD based field effect transistors (FETs). In this work, we employ Density Functional Theory (DFT) calculations to analyze the modulation of the electronic structure of monolayer WS 2 with chlorine doping and the relative changes in the contact properties when interfaced with gold and palladium. We initially examine the atomic and electronic structures of pure and doped monolayer WS 2 supercell and explore the formation of mid gap states with band splitting near the conduction band edge. Further we analyze the contact nature of the pure supercell with Au and Pd. We find that while Au is physiosorped and forms n-type contact, Pd is chemisorped and forms p-type contact with a higher valence electron density. Next, we study the interface formed between the Cl-doped supercell and metals and observe a reduction in the Schottky barrier height (SBH) in comparison to the pure supercell. This reduction found is higher for Pd in comparison to Au which is further validated by examining the charge transfer occurring at the interface. Our study confirms that Cl doping is an efficient mechanism to reduce the n-SBH for both Au and Pd which form different types of contact with WS 2 .After the fabrication of FET using monolayer MoS 2 , 1 2D layered transition metal dichalcogenides(TMDs) have garnered enormous attention in the electron devices community. Apart from MoS 2 , other TMDs as such WS 2 2,3 , WSe 2 4 , MoSe 2 5 and MoTe 2 6 are also explored as channel material for FET's. In the absence of efficient doping techniques, these transistors exhibit SBH at source/drain contact which leads to low ON current. Tremendous efforts are dedicated to reduce the contact resistance at TMD-metal interface by employing different techniques both theoretically and experimentally. [7][8][9][10][11][12] However, most of these efforts are focused towards MoS 2 and WSe 2 and a minimum study is devoted to other TMD'smetal contact interfaces. A study using ballistic MOSFET model reveals that WS 2 outperforms all other TMD's 13 . Experimental reports of WS 2 device fabrication 2 and Cl doping technique for reducing WS 2 -metal contact resistance are also reported 14 . However, theoretical investigations of WS 2 metal contact interface using first principles is still lacking in the literature. Since first principles are extensively used to analyze the graphene-metal 15,16 , MoS 2 -metal 17 and WSe 2 -metal 18 , it is believed that it will efficiently describe the contact nature with other TMD's as well. For WS 2 , chlorine doping, which is done by replacing sulfur atoms is the first ever method demonstrated experimentally to reduce the WS 2 -contact resistance, exhibiting both high drain current and field-effect mobility. 14 In this work we employ density function theory (DFT) to study the electronic structure of the interface between WS 2 and one physiosorped (Au) and one chemisorped (Pd) metal. We then examine the effect of chlorine doping by substituti...

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