Reconfiguration of Intrinsic Depletion-Mode Characteristics of MoS2 Field-Effect Transistors to High-Performance Enhancement-Mode Operation Using an Argon Plasma-Induced p-Type Doping Technique.

Abstract

The intrinsic n-type behavior and unavailability of the appropriate p-type doping method for MoS₂ allows only n-type conduction with depletion mode (D-mode) characteristics and forbids the implementation of p-type field-effect transistors (FETs). The D-mode characteristic results in a high off-current (I_OFF) at zero gate bias, which limits the usage of MoS₂ FETs for industry-scale (n-channel metal-oxide semiconductor) NMOS/(complementary metal-oxide semiconductor) CMOS-logic-based applications due to significant power dissipation. Both these issues, i.e., i) missing technique for p-type doping and ii) D-mode operation are addressed here through the application of argon (Ar) plasma and subsequent O₂ bath. Here, Ar plasma results in the physical removal of sulfur (S) atoms from the MoS₂ surface, introducing sulfur vacancies, and the O₂ bath results in the chemical bonding of O₂ molecules with molybdenum (Mo) atoms at the introduced S vacancy sites. This leads to the formation of shallow acceptor states near the valance band (VB) of MoS₂, resulting in p-type doping and enhancement mode (E-mode) characteristics of MoS₂ FETs. Moreover, using Ar plasma results in the reduction of contact resistance (R_C) of E-mode MoS₂ FETs and hence facilitates achieving high-performance top-gated E-mode MoS₂ FETs with I_OFF (at zero gate bias) in tens of picoamperes and I_ON/I_OFF in seven orders.