Effects of the impurity-impurity and impurity-host interactions on the charge density and the related processes

Transitions via impurities, in addition to transitions from the valence band to the conduction band in semiconductors increase the generation of electron-hole pairs. These transitions lead to alterations in the electronic density around the impurities, and as a consequence, to modifications in the forces on the impurities. In many cases it leads to an increase in the non-radiative recombination. The understanding of these processes at an atomic scale is very important for the physics of doped semiconductors, and technologically, for optoelectronic and spintronic devices. Using simple approximate models based on first-principles, the charge density and the related processes are analyzed. The results show that an increase in the impurity-host interaction or an increase in the concentration of the impurity leads to small variations in the density around the impurities for different charge states and a decrease in the effective Coulomb repulsion. These facts reduce the mechanism of non-radiative recombination via multi-phonon emission.