Seong Yeoul Kim1,Xinglu Wang1,Roy Joy1,Robert Wallace1
The University of Texas at Dallas1
Seong Yeoul Kim1,Xinglu Wang1,Roy Joy1,Robert Wallace1
The University of Texas at Dallas1
The issue of high contact resistance (R<sub>c</sub>) has remained an unsolved issue for transition metal dichalcogenides (TMDs) and it became more significant in sub-nano channel lengths. While the recent findings on bismuth (Bi) metal contacts on MoS<sub>2</sub> have reported remarkably low contact resistance and high on-current density, these results are not yet fully established.[1] It is necessary to first understand the interfacial chemistry and the band alignment between Bi and TMDs because the Fermi level may vary depending on the interfacial properties.[2]<br/> In this work, the interface properties of Bi/TMDs (MoS<sub>2</sub>, MoSe<sub>2</sub>, WS<sub>2</sub>, and WSe<sub>2</sub>) are investigated by utilizing an <i>in-situ</i> ultrahigh vacuum (UHV) cluster system including X-ray photoelectron spectroscopy (XPS) and an e-beam evaporator.[3] Metallization and interface analysis was conducted within UHV conditions to allow the precise investigation of the Bi/TMDs interface made possible by suppressing the effect of contamination from the ambient. Band alignments were investigated by using XPS core-level shift and valence band maximum spectra of the Bi/TMDs interface. The Fermi levels of the Bi/TMD interfaces are formed close to the conduction band minimum for all investigated TMDs after Bi deposition. Additionally, it was found that bonding associated with interfacial reaction of Bi/TMDs was below the limit of XPS detection (< 1 at. %). Based on the atomic force microscopy (AFM), Bi metal follows a Volmer-Weber (VM) growth mode consistent with a lack of interaction between Bi and TMDs. Ultimately, these results show that Bi forms van der Waals (vdW) interface with n-type contact properties on variable TMDs semiconductor materials.<br/><br/>Add acknowledgment for NEWLIMITS and NSF project: “This work was supported in part by NEWLIMITS, a center in nCORE, a Semiconductor Research Corporation (SRC) program sponsored by NIST through award number 70NANB17H041, and the National Science Foundation (DMR 2002741).<br/><br/>[1] Shen et al. <i>Nature</i> <b>2021</b>, <i>593</i> (7858), 211–217.<br/>[2] Wang et al. <i>ACS Appl. Mater. Interfaces</i> <b>2021</b>, <i>13</i> (13), 15802–15810.<br/>[3] Wallace, R.M. <i>ECS. Trans.</i> <b>2008</b>, <i>16 </i>(5) 255-271.