Chemical vapor deposition of ZnS:Mn for thin-film electroluminescent display applications

Abstract

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. © Materials Research Society 2004.