Effect of Se vapor pressure and thermal dissociation process on excitonic-emission lines in molecular beam epitaxially grown high-purity zinc selenide

It has been found that two dominant bound-exciton (BE) emission lines at 2.7954 and 2.7815 eV in the not-deliberately-doped ZnSe single crystal layers grown by molecular beam epitaxy, can be strongly affected by heat treatment in controlled Se vapor pressure. The emission intensity of the 2.7954-eV line was shown to decrease remarkably with increasing Se vapor pressure and from its temperature dependence the line is ascribed to the recombination of excitons bound to a neutral donor whose ionization energy is about 36 meV. On the other hand, the 2.7815-eV line, which is due to the recombination of a neutral acceptor BE, became more intense and sharp with increasing Se vapor pressure. The characteristics of the principal BE lines variable with Se vapor pressure are discussed.