CHEMICAL VAPOR-DEPOSITION OF ZNS-MN ELECTROLUMINESCENT FILMS IN A LOW-PRESSURE HALOGEN TRANSPORT-SYSTEM

A new technique to produce a manganese-doped zinc-sulfide (ZnS) electroluminescent (EL) film has been developed using a low-pressure chemical vapor deposition system. The Mn2+ ions are doped in the ZnS layer by controlling the flow rate of the hydrogen-chloride (HCl) carrier gas. Undoped ZnS films show <111>-oriented cubic structure, whereas the Mn-doped ZnS films have hexagonal structure with <00.1> preferred orientation. The crystal structure changes from cubic to hexagonal with incorporation of the Mn-dopant. The single crystal layers are epitaxially grown on a silicon substrate at 500-degrees-C. A strong blue-light emission originating from a self-activated center is observed in the photoluminescence spectra. This blue band, however, is rapidly quenched with increasing the Mn concentration. It is clarified that a competitive adsorption phenomenon between Zn-Cl2 and Mn-Cl2 species on the growing surface plays an important role in the growth process and the film characteristics. A high efficiency of 4 lm/W and a steep luminance-voltage curve with a saturation luminance exceeding 3500 cd/m2 are obtained in a device with double insulator structure under 1 kHz excitation. The crystalline properties and luminescence characteristics are discussed in terms of the effect of the Mn-doping and the growth temperature.