  A fundamental understanding of the intrinsic optoelectronic properties of
atomically thin transition metal dichalcogenides (TMDs) is crucial for its
integration into high performance semiconductor devices. Here, we investigate
the transport properties of chemical vapor deposition (CVD) grown monolayer
molybdenum disulfide (MoS2) under photo-excitation using correlated scanning
photocurrent microscopy and photoluminescence imaging. We examined the effect
of local phase transformation underneath the metal electrodes on the generation
of photocurrent across the channel length with diffraction-limited spatial
resolution. While maximum photocurrent generation occurs at the Schottky
contacts of semiconducting (2H-phase) MoS2, after the metallic phase
transformation (1T-phase), the photocurrent peak is observed towards the center
of the device channel, suggesting a strong reduction of native Schottky
barriers. Analysis using the bias and position dependence of the photocurrent
indicates that the Schottky barrier heights are few meV for 1T- and ~200 meV
for 2H-contacted devices. We also demonstrate that a reduction of native
Schottky barriers in a 1T device enhances the photo responsivity by more than
one order of magnitude, a crucial parameter in achieving high performance
optoelectronic devices. The obtained results pave a pathway for the fundamental
understanding of intrinsic optoelectronic properties of atomically thin TMDs
where Ohmic contacts are necessary for achieving high efficiency devices with
low power consumption.
