PHOTOLUMINESCENCE PROPERTIES OF ZNS EPILAYERS

A comprehensive study is reported of the photoluminescence properties of ZnS thin films between 1.6 and 320 K grown by metalorganic molecula r beam epitaxy and chemical beam epitaxy on GaAs substrates. Both heav y- and light-hole free excitons were observed at low temperatures with linewidths of 7.0 and 5.3 meV, respectively, as well as donor- and ac ceptor-bound excitons and free-to-bound recombination along with their longitudinal optical (LO) phonon replicas. The free exciton emission was observed up to 320 K, and enabled the room temperature band gap of ZnS to be unambiguously determined as 3.723 eV. The temperature depen dence of the peak position, intensity, and linewidth was well describe d by the conventional empirical relations and by Toyozawa's exciton li ne shape theory. The bound exciton peak positions were found to follow the temperature dependence of the band gap whereas the free-to-bound recombination feature was displaced by (1/2)kT above the band gap ener gy. Thermal quenching of the donor-bound exciton was described by a on e-step quenching process with an activation energy of 14.4 meV. The se lf-activation (SA) center was also observed at 2.846 eV with a linewid th of 410 meV. The temperature dependence of the SA emission was well described by the configuration coordinate model. From the thermal broa dening of the SA emission, an average phonon energy of 47.5 meV was de termined in good agreement with the LO phonon energy. (C) 1997 America n Institute of Physics.