Microscopic Analysis of the Valence Band and Impurity Band Theories of (Ga,Mn)As


We resolved a long-standing controversy between the valence-band and impurity-band picture of diluted magnetic semiconductors (Ga,Mn)As. We calculated the electron density of states for varying content of Mn and showed that no detached impurity band is formed in ferromagnetic materials. The dependence of the Fermi energy on chemical composition is consistent with observed blue shift in infrared absorption spectra and magnetic circular dichroism.

A detailed analysis of various versions of the impurity-band model shows their inconsistency: the width of the impurity band quickly increases with increasing concentration of Mn, the impurity states merge with the valence band already at very small content of Mn, and Fermi energy moves towards the conduction band even faster then for the valence-band picture, in a contradiction to basic assumptions of the impurity-band picture.