  In this present study, we systematically investigated the structural,
electronic, optical and transport properties of pristine and group II, group
IVa doped GaS monolayers using density functional theory (DFT). The strong
formation energy suggests realization of group II & group IVa doped GaS. A
semiconductor to metallic transition occurs in GaS monolayer with doping.
Moreover, doped GaS monolayers have shown tunable optical properties. Doped GaS
monolayers show optical activity in both ultraviolet (UV) as well as visible
region. EEL spectra of GaS shift towards high energy region (red shift) with
group II elements doping while no significant shift is observed for group IVa
elements doping in both the polarizations. We found quantum conductance of 4G0
for doped GaS monolayer except for Be-doped GaS. The metallic character of
doped GaS is clearly captured in tunneling current characteristics showing
ohmic-like characteristics for doped GaS monolayer. This is due to finite
density of states associated with S atoms of doped GaS. The doping extends the
functionalities of pristine GaS with tunable properties suggesting doped GaS as
a potential candidate for use in photo-diodes, photo-catalysts, photo-detectors
and bio-sensing.
