Metal–Insulator Transition and superconductivity in doped semiconductors

Using the effective mass theory and the variational method, the critical concentrations of shallow donors in Si at which the Mott Transition occurs are obtained. Our theory uses the experimentally available donor ionization energies in the low-concentration regime and a mass variation with interimpurity distance to account for the impurity bands. Since the experimentally available donor ionization energies are used, the central-cell effects and valley–orbit interactions are taken into account. Excellent agreement with the available experimental results is obtained for P, As, Sb and Bi donors in Si. Since the critical concentration at which superconductivity occurs in B doped Si is established recently, we predict the concentrations at which superconductivity should occur for these donors also.