Optical transitions in (ZnCo)Se and (ZnFe)Se: Role of an effective p-d exchange (invited)

In this paper we discuss photoluminescence (PL) and Raman excitations in the diluted magnetic semiconductors Zn1-xCoxSe and Zn1-xFexSe. The PL spectra associated with isolated crystal field d levels are found to rapidly weaken and/or broaden as the transition metal ion concentration approaches and increases beyond a critical value. In addition a Raman continuum, that overlaps with the optical phonon, is observed to develop when the PL features are modified. In the corresponding Zn1-xCoxSe samples the optical phonons acquire a characteristic Fano line shape suggestive of its coupling to the Raman continuum. It is proposed that these changes to the optical transitions arise from the enhancement of an effective p-d hybridization between low-lying d levels and band electrons with increasing x - an effect largely due to the proximity of the Co2+and Fe2+crystal field ground levels to the valence band maximum.