Schematic images of the object of study: (a, b) metal-dielectric-undoped semiconductor structure and band diagram in thermodynamic equilibrium: M – metal (Ti), 1 – Al2O3, 2, 4, 6 – GaAs, 3, 5 – AlGaAs, Φm – work function of Ti, χ1, χs – electron affinity of Al2O3 and GaAs, working layer 4 is empty; (c, d) a variant of the operating mode corresponding to a 2DHG (T ~ 1 K, eVTG < 0 is the difference of the Fermi levels in the working layer and the upper gate).