  The disentanglement of single and many particle properties in 2D
semiconductors and their dependencies on high carrier concentration is
challenging to experimentally study by pure optical means. We establish an
electrolyte gated WS2 monolayer field-effect structure capable to shift the
Fermi level from the valence into the conduction band suitable to optically
trace exciton binding as well as the single particle band gap energies in the
weakly doped regime. Combined spectroscopic imaging ellipsometry and
photoluminescence spectroscopies spanning large n- and p-type doping with
charge carrier densities up to 10^14 cm-2 enable to study screening phenomena
and doping dependent evolution of the rich exciton manifold whose origin is
controversially discussed in literature. We show that the two most prominent
emission bands in photoluminescence experiments are due to the recombination of
spin-forbidden and momentum-forbidden charge neutral excitons activated by
phonons. The observed interband transitions are redshifted and drastically
weakened under electron or hole doping. This field-effect platform is not only
suitable for studying exciton manifold but is also suitable for combined
optical and transport measurements on degenerately doped atomically thin
quantum materials at cryogenic temperatures.
