  Atomic vacancies, such as chalcogen vacancies in 2D TMDs, are important in
changing the host material's electronic structure and transport properties. We
present a straightforward one-step method for growing monolayer MoS2 utilizing
oxidized Molybdenum (Mo) foil using CVD and delve into the transport properties
of as-grown samples. Devices fabricated from these MoS2 sheets exhibit
excellent electrical responses, with the standout device achieving mobility
exceeding 100 cm2V-1s-1. Structural analysis and optical signatures unveiled
the presence of chalcogen defects within these samples. To decipher the
influence of inherent defects on the electronic transport properties, we
measured low-temperature transport on two distinct sets of devices exhibiting
relatively high or low mobilities. Combining the thermally activated transport
model with quantum capacitance calculations, we have shown the existence of
shallow states near the conduction band, likely attributed to sulfur vacancies
within MoS2. These vacancies are responsible for the hopping conduction of
electrons in the device channel. Furthermore, our claims were substantiated
through low-temperature scanning tunnelling microscopy measurements, which
revealed an abundance of isolated and lateral double sulfur vacancies in Mo
foil-grown samples. We found that these vacancies increase the density of
states near the conduction band, inducing intrinsic n-type doping in the MoS2
channel. Consequently, this elevated conductivity enhances the field-effect
mobility of MoS2 transistors. Our study offers insights into chalcogen
vacancies in CVD-grown monolayer MoS2 and highlights their beneficial impact on
electronic transport properties.
