Metal-Nonmetal Transition in Doped Semiconductors

The metal-nonmetal (M-NM) transition observed in some doped semiconductors is discussed on the basis of the Mott-Hubbard-Anderson scheme. A classification of characteristic donor (acceptor) concentration regions is given. The M-NM transition concentration is defined as a concentration at which the states corresponding to the Fermi level become delocalized. Several experimental data near the transition concentration are analyzed and interpreted as lending support to the above-mentioned scheme. A possible picture concerning the position of the Fermi level relative to the mobility gap is proposed and some experimental results are described, which are explained in consistent with this picture.