Magnetic-field-induced metal-nonmetal transition in GaAs-${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$As heterostructures

The metal-nonmetal transition in GaAs-${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Al}}_{\mathrm{x}}$As heterostructures has been investigated using electrical conductivity and Hall measurements in the presence of a magnetic field and hydrostatic pressure. The binding energy of a magnetodonor, composed of donor atoms and electrons separated from each other by a spacer, has been measured as a function of magnetic field for different surface densities controlled by the pressure. A simple model is presented which accounts qualitatively for the observed effects.