Direct evidence for screening of the Coulomb interaction in quasi-two-dimensional systems

Magnetic freeze-out of inversion electrons into bound Si donors in GaAs-${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Al}}_{\mathrm{x}}$As heterostructures with a spacer has been investigated experimentally and compared with the theory. An inclusion of screening of the Coulomb interaction between electrons and donors is essential for the description of magneto-donor behavior. Features related to overlap of the donor wave functions and the resulting metal-nonmetal transition are demonstrated and discussed.