  The effect of doping on the parameters of an electron-hole liquid (EHL) in
heterostructures based on transition metal dichalcogenides is studied. The
phase diagram of the EHL is constructed. It is shown that for the formation of
a high-temperature tightly bound EHL, as well as for the transition from the
semiconducting (exciton) state to the semimetallic one (electron-hole
plasma/liquid), it is advantageous to dope the energy band with larger number
of valleys. The transition from trion gas to electron-hole plasma is
investigated using the modified Mott criterion and variational calculation with
screened potential. The effect of doping on the metal--insulator transition in
the equilibrium case without laser excitation is studied.
