Electronic structure and migrational properties of interstitial zinc in ZnSe

We report optically detected electron paramagnetic resonance via photoluminescence in ZnSe after in situ 4.2 K irradiation with 2.5 MeV electrons. The isolated interstitial is identified in the Td site surrounded by four zinc atoms, (Znᵢ)Zn⁺, as well as in the Td site surrounded by four Se atoms, (Znᵢ)Se⁺. Analysis of the central ⁶⁷Zn and neighboring ⁷⁷Se atom hyperfine interactions for the two sites, plus other considerations, allows estimates of their second donor levels to be at ~1.6 and ~1.0 eV below the conduction band, respectively. Migration of the interstitial under optical excitation at 1.5--25 K is detected by monitoring its cyclic conversion between the two configurations, as well as by interconversion between various close zinc-interstitial--zinc-vacancy Frenkel pairs. The dependence of the process on temperature, excitation wavelength and intensity, and sample history is described, and a possible model for the mechanism is proposed.