Influence of metal-induced doping on different 2D MoS2 epilayers for field effect transistors

Molybdenum disulfide (MoS2), a prominent member of the transition metal dichalcogenide family, stands out for its unique electronic and optical properties. To date, it is not well understood how doping works with distinct epitaxial layers to metal deposition. We investigate the charge doping effects of Bi and Au on MoS2 using Raman spectroscopy and transport measurements with Bi contacts, analyzing how doping influences epilayer growth and the electrical characteristics of coalesced monolayer (1L) and bilayer (2L) MoS2. We observe that coalesced 1L MoS2 provides a surface conducive to homogeneous doping, while regions with 2L MoS2 exhibit almost no signature for doping but improved device performance due to its enhanced carrier density. Specifically, our results show that field-effect transistors with Bi-contacted 2L MoS2 channels offer approximately 5× higher current density, 1.8× lower contact resistance (RC), and 2× greater field-effect mobility compared to 1L channels. However, 1L MoS2 retains a superior on/off current ratio, exceeding 108, while the on/off ratio for 2L MoS2 is approximately 106. The findings shed light on the interplay between epitaxial layers and metal deposition, offering valuable insights into tailoring MoS2 devices to meet the demands of advanced electronic applications for enhanced performance and functionality.