IDENTIFICATION OF NA ACCEPTOR IN MOCVD-GROWN ZNS FILMS AND THE EFFECT OF UV-LIGHT ILLUMINATION

Low-temperature photoluminescence (PL) studies have been carried out to identify a Na acceptor level in ZnS films grown by low-pressure metalorganic chemical-vapour deposition. A neutral Na acceptor bound-exciton line at 3.781 eV and related edge-emission bands at about 3.67 eV were observed. In particular, the edge-emission band is attributed to a free-to-Na acceptor transition by a time-resolved spectra experiment. These PL properties have also been investigated by changing growth and Na cell temperatures. The ionization energy of the Na acceptor is estimated to be about 170 meV which is in good agreement with the theoretical value calculated by Baldereschi and Lipari. The effect of UV light illumination was preliminary done to incorporate Na impurities into ZnS films during epitaxial growth. It was found that the Na acceptor bound-exciton line can be significantly enhanced in intensity. © 1989.