Effects of photoassisted deposition and/or photoassisted annealing on characteristics of ZnS:Mn thin-film electroluminescent devices

Abstract

Some essential photoinduced effects on the characteristics of ZnS:Mn electron-beam evaporated films and thin-film electroluminescent (TFEL) devices based on them have been revealed when Hg-lamp irradiation and quartz halogen lamp illumination are used during deposition and postannealing, respectively. The photoassisted deposition with the irradiation of the ZnS:Mn flux or a substrate results in some improvement of the crystal structure of the films, an enhancement of the intensity of photoluminescence and electroluminescence (EL), an increase of the threshold voltage of EL and the luminous efficiency, a lesser change and the quicker stabilization of EL characteristics during short-term forced aging. The use of the photoassisted rapid annealing instead of a usual long-term annealing in a vacuum furnace causes some enlargement of the crystallites and the improvement of performance of the TFEL devices. Both photoassisted processes used lead to a significant reduction of the impurity photocurrent in the photodepolarization spectra. The above results indicate that the following photoinduced changes take place in the ZnS:Mn film: a more densely packed lattice, an increase of the energy depth of the free-electron source, a decrease of the number of pores and defects, particularly, the defects responsible for the radiationless processes and the instability of the EL characteristics in the course of the device operation. Possible mechanisms of the photoinduced effects are discussed.