Optical evidence of strong coupling between valence-band holes andd-localized spins inZn1−xMnxO

Abstract

We report on optical-absorption study of ${\text{Zn}}_{1-x}{\text{Mn}}_x\text{O}$ $\left(x=0–0.06\right)$ films on fused silica substrates taking special attention to the spectral range of the fundamental absorption edge (3.1–4 eV). Well-pronounced excitonic lines observed in the region 3.40–3.45 eV were found to shift to higher energies with increasing Mn concentration. The optical band-gap energy increases with $x$ too, reliably evidencing strong coupling between oxygen holes and localized spins of manganese ions. In the 3.1–3.3 eV region the optical-absorption curve in the manganese-contained films was found to shift to lower energies with respect to that for undoped ZnO. The additional absorption observed in this range is interpreted as a result of splitting of a localized Zhang-Rice-type state into the band gap.