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 $T_d$ site surrounded by four zinc atoms, $({\mathrm{Zn}}_i{)}_{\mathrm{Zn}}^{+},$ as well as in the $T_d$ site surrounded by four Se atoms, $({\mathrm{Zn}}_i{)}_{\mathrm{Se}}^{+}.$ Analysis of the central ${}^{67}\mathrm{Zn}$ and neighboring ${}^{77}\mathrm{Se}$ atom hyperfine interactions for the two sites, plus other considerations, allows estimates of their second donor levels to be at $\sim 1.6$ and $\sim 1.0\hspace{0.5em}\mathrm{eV}$ 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.