Novel Inorganic DC Lateral Thin Film Electroluminescent Devices Composed of ZnO Nanorods and ZnS Phosphor
- PDF / 506,079 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 43 Downloads / 229 Views
1144-LL19-21
Novel Inorganic DC Lateral Thin Film Electroluminescent Devices Composed of ZnO Nanorods and ZnS Phosphor Tomomasa Satoh, Yuki Matsuzawa, Hiroaki Koishikawa, and Takashi Hirate Faculty of Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama, Japan ABSTRACT A novel inorganic thin-film electroluminescence (TFEL) device exhibiting bright EL emission when driven by a low DC voltage is demonstrated. The DC-TFEL device is based on a composite layer in which aluminum-doped ZnO nanorods are vertically embedded in ZnS:Mn as an EL phosphor. The DC driving voltage is then applied laterally to the composite layer via two side electrodes set 3.5 mm apart. The aluminum-doped ZnO nanorods were synthesized on a glass substrate by low-pressure thermal chemical vapor deposition combined with laser ablation, and the composite layer was formed by electron-beam deposition of ZnS:Mn onto the ZnO nanorods. The thickness of the composite layer was about 160 nm. After electrical modification to breakdown a basal conduction ZnO path, the lateral DC-TFEL device exhibited bright EL emission without avalanche breakdown, achieving a luminance of 747 cd/m2 at 4200 V with a luminous efficiency of 9.2×10-3 lm/W. INTRODUCTION The commercial market for flat panel displays is presently dominated by liquid crystal and plasma technology following considerable progress in performance and cost reduction for these technologies. Organic light-emitting diodes (OLEDs) have recently attracted much attention as a promising technology for the next generation of flat panel displays. In contrast, the development of inorganic thin-film electroluminescent (TFEL) devices, also a promising display technology, lacks momentum. The slow progress in TFEL devices can primarily be attributed to the lack of an efficient blue EL phosphor, as well as the high AC voltage required to drive the devices. As efficient inorganic blue EL phosphors such as BaAl2S4:Eu have now been developed [1,2], only the problems of driving voltage remain to be addressed. A lower DC voltage is highly desirable for driving TFEL devices. The requirement for a high AC voltage stems from the basic operation of inorganic EL phosphors, which require high electric fields of the order of 106 V/cm to induce emission. However, such high electric fields cause avalanche breakdown of the EL host material. Conventional inorganic TFEL devices therefore have a thin-film stack structure consisting of a phosphor layer sandwiched between two insulators, which necessitates an AC driving voltage. To obtain EL emission at lower voltages, the phosphor layer and the insulator layers must be made thinner, and the driving voltage must be applied vertically to the stack via one opaque and one transparent electrode. However, a driving voltage of higher than 200 V is required even for the minimum practical thicknesses of the phosphor and insulator layers. It is thus difficult to realize further decreases in the electric field required to induce emission of the EL active layer. To achieve a
Data Loading...
