Resonant State of Substitutional Oxygen in ZnSe

We have studied the effect of hydrostatic pressure on low- temperature photoluminescence (PL) spectra of ZnSe doped with oxygen. MBE-grown samples containing up to 2x10$^{19}$/cm$^{3}$ of oxygen have been studied. A broad PL spectral feature associated with the O-states emerges at the pressures around 30- 40 kbar as the fundamental bandgap of ZnSe increases with pressure. It gradually becomes the predominant emission structure and shifts towards higher energy with increasing pressure but at a much slower rate than the exciton emission in ZnSe. By extrapolating the experimental data to the atmospheric pressure, the energy position of the resonant O-states is found to be $\sim$0.20 eV above the conduction-band edge of ZnSe. The location of the resonant state provides a key parameter for modeling the electronic structure of highly mismatched ZnO$_{x} $Se$_{1-x}$ alloy.