IMPURITY-INDUCED NARROW BANDS OF CONTINUOUS ELECTRONIC STATES IN DOPED SEMICONDUCTORS

Impurity-induced modification of the density of electronic states in t ransition-metal-doped semiconductors is studied. The model Hamiltonian includes potential scattering of band electrons by impurity atoms ran domly distributed in the host lattice, and hybridization between initi al band states and d orbitals. The bare levels of the atoms are locate d in the band gap. By applying multiple-scattering theory, configurati on-averaged Green functions over the impurity ensemble are calculated by using the Matsubara method in the short-range potential approximati on. We demonstrate that for the defined attractive impurity potentials the potential scattering results in band tail formation. A narrow hig h-density band of free states within the gap have been found. The band is caused by the hybridization that induces the following virtual ele ctron transitions over the impurity ensemble: an initial impurity site --> a band state --> another site --> a band state, etc. It is essent ial that the main high-density peak of the localized states lies withi n this band.