The metal-insulator transition in the impurity band of n-type GaAs induced by a magnetic field and loss of dimension

Abstract

Experiments have been performed on the metal—insulator transition in the impurity band of n-type GaAs induced by a high magnetic field. A transition from three to two-dimensional transport has been observed by varying the thickness of the conducting layer with a Schottky barrier gate. When transport is three dimensional the minimum metallic conductivity is in agreement with theory but when transport is two-dimensional the minimum metallic conductance, in the presence of the magnetic field, is less than, the predicted value. It is suggested that within the lower Hubbard band, the mobility edge is a function of carrier concentration (in the absence of compensation) and increases as the Fermi energy increases, implying that its location is not determined solely by the disorder arising from the impurity ions.