Ultraviolet Light Emitting Devices Using AlGdN
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Ultraviolet Light Emitting Devices Using AlGdN Takashi Kita1, Shinya Kitayama1, Tsuguo Ishihara2, Hirokazu Izumi2, Yoshitaka Chigi3, Tetsuro Nishimoto3, Hiroyuki Tanaka3, and Mikihiro Kobayashi3 1 Department of Electrical and Electronics Engineering, Graduate School of Engineering, Kobe University, Rokkodai 1-1, Nada, Kobe 657-8501, Japan 2 Hyogo Prefectural Institute of Technology, Yukihira 3-1-12, Suma, Kobe 654-0037, Japan 3 YUMEX INC., Itoda 400, Yumesaki, Himeji, Hyogo 671-2114, Japan ABSTRACT We developed ultra-violet field-emission devices using rare-earth nitrides of Al1-xGdxN grown by a reactive radio-frequency magnetron sputtering technique. The Al1-xGdxN phosphor film excited by high-energy electrons shows a resolution limited, narrow intra-orbital luminescence from Gd3+ ions at 318 nm. The devise characteristics depend on injected current and acceleration voltage, which were analyzed by considering multiple excitation process of injected high-energy electrons. INTRODUCTION Ultra-violet (UV) light is indispensable for various industrial processes such as lithography, curing, polymerization using photochemical reactions, sterilization, and medical treatment. For these applications, many kinds of discharge lamps using mercury have been widely used in such fields. However, mercury is recognized as a chemical of global concern due to its long-range transport in the atmosphere, its persistence in the environment, its ability to bioaccumulate in ecosystems and its significant negative effect on human health and the environment. For human life free from mercury, it is strongly desired to develop novel UV lighting source which can replace currently available mercury lamps. Recently, nitridesemiconductor based UV light emitting diodes (LEDs) are attracting strong interest.[1] In LEDs, the emission wavelength can be controlled by the optical band gap, and efficient light emission is realized by utilizing quantum structures. However, the spectral line width limited by the thermal carrier distribution near the band edge causes a relatively broad emission-band width being generally over 10 nm. Moreover, when we need to irradiate large area with the UV light, the flux from a small LED chip must be controlled to prepare uniform power distribution on the large area. Such point source of LEDs with the broad band emission is unfortunately limiting the application. For photo lithography to obtain the high resolution and medical applications to avoid unexpected side effects, light panel with a narrower spectral width is required. Instead of using band-edge emission, we focus on the use of narrow band emissions from the intra-orbital electron transitions of rare earth ions.[2-4] Rare earth ions are widely used in various phosphors, solid state laser crystals, and optical amplifiers. In this work, we focus on Gd which emits the luminescence near 300 nm. To avoid absorption of the UV emission, the host material must have a wide bandgap more than 4 eV. AlN is suitable for this requirement.[5-8] The band gap is approximately 6.2
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