Chemical Vapor Deposition of ZnS:Mn for Thin-Film Electroluminescent Display Applications

Results are presented from a systematic investigation to design and optimize a low-pressure chemical vapor deposition (CVD) process for manganese-doped zinc sulfide (ZnS:Mn) thin films for electroluminescent (EL) device applications. The CVD process used diethylzinc (DEZ), di-π-cyclopentadienyl manganese (CPMn), and hydrogen sulfide (H₂S) as co-reactants and hydrogen (H₂) as carrier gas. A design of experiments approach was used to derive functionality curves for the dependence of ZnS:Mn film properties on substrate temperature and flow rates (partial pressures) of DEZ, CPMn, H₂S, and H₂. Film physical, chemical, structural, and optical properties were examined using Rutherford backscattering spectrometry, dynamic secondary ion mass spectroscopy, x-ray photoelectron spectroscopy, nuclear-reaction analysis, x-ray diffraction, transmission electron microscopy, atomic force microscopy, and scanning electron microscopy. EL measurements were carried out on ZnS:Mn-based dielectric–sulfur–dielectric stacks incorporated into alternating-current thin-film electroluminescent devices. An optimized process window was established for the formation of films with predominantly (0 0 2) orientation, grain size larger than 0.2 μm, and Mn dopant level approximately 0.5 at.%. A brightness of 407 cd/m² (119 fL) and efficiency of 1.6 lm/W were obtained, as measured at 40 V above threshold voltage and 60 Hz frequency.