Mixed-valent states of rare-earth dopants in IV-VI semiconductors

Mixed-valent states of rare-earth dopants in narrow-gap IV-VI semiconductors are analyzed. A theoretical approach to describing rare-earth-doped IV-VI semiconductors is proposed in which the dopant is considered a strongly correlated system, with electronic states coupled to conduction- and valence-band states. The results are illustrated by the example of the Yb dopant, having an almost-filledfshell. It is shown that the system can be described by a narrow resonance level, whose position and width depend on the chemical potential and band gap. The possibility of the formation of mixed-valent states is demonstrated.