OPTICAL CHARACTERIZATION OF ULTRA-HIGH-PURITY ZINC SELENIDE EPILAYERS

We studied, by photoluminescence (PL) and PL excitation spectroscopies, unintentionally doped ZnSe epilayers, grown by molecular beam epitaxy using ultra-high-purity sources of zinc and selenium. We find that the PL from such samples is dominated by free excitonic transitions with weak contributions from transitions due to donor-bound excitons. In particular, we discuss a possible origin of a peak I0v located at 22380 cm-1 (2.7738 eV). Selective PL and PL excitation experiments conclusively show that I0v is due to an independent transition and not related to excitonic processes. We also find that as we increase Zn/Se beam pressure ratio, an increase in the intensity of I0v is observed. In addition, the coupling constant for I0v to LO phonons is found to be ≈0.04 which is very weak considering the fact that its localization energy of ≈29 meV is very large. These observations together with the fact that the full width at half maximum for I0v is ≈2 meV, which is large compared to <1 meV for typical impurity-bound exciton lines, lead us to tentatively suggest that I0v may be a result of recombinations involving states due to localized defects or complexes. © 1989.