Impact of the Schottky Barrier and Contact‐Induced Strain Variations inside the Channel on the Electrical Behavior of Monolayer MoS2 Transistors

Strain-dependent electronic and optical properties are one of the most appealing features of 2D semiconductors, like monolayer (1L) MoS2. However, measuring and controlling the homogeneity of strain within the channel is crucial for next-generation MoS2 field-effect transistors (FETs). This article reports a multiscale investigation of backgated FETs fabricated using large-area 1L MoS2 flakes grown by liquid-precursor-intermediated chemical vapor deposition on SiO2/Si substrates. The devices exhibit very attractive properties for ultra-low power applications, such as an Ion/Ioff > 106 and a normally off electrical behavior. The combination of temperature-dependent analyses of the FET transfer characteristics and nanoscale resolution potential mapping by Kelvin probe force microscopy shows a fully depleted MoS2 channel at VG = 0 and an effective Schottky barrier ΦB,FB = 0.21 eV at flatband voltage VFB = 17.9 V. An inhomogeneous tensile strain (ε) distribution along the channel length is revealed by micro-Raman and photoluminescence (PL) mapping, with a reduced ε and blue-shifted PL energy close to the Ni/Au source/drain contacts, suggesting a biaxial compression of 1L MoS2 induced by metal deposition. The implications of these observations on the effective mass meff variation along the channel and the current injection from source/drain contacts have been discussed in the perspective of future ultra-scaled-devices applications.