High Efficiency UV-Emission at 345 nm from InAlGaN Light-Emitting Diodes
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High Efficiency UV-Emission at 345 nm from InAlGaN Light-Emitting Diodes A. Kinoshita1 2, H. Hirayama1, M. Ainoya1 2, T. Yamabi1 2, A. Hirata and Y. Aoyagi1 1 The Institute of Physical and Chemical Research (RIKEN), Hirosawa 2-1, Wako-shi, Saitama, 351-0198, Japan 2 Department of Chemical Engineering, Waseda University, Okubo 3-4-1, Shinjuku-ku, Tokyo, 169-8555, Japan ABSTRACT Optical and electrical properties of 340 nm-band bright UV-light emitting diodes (LEDs) were compared between In0.03Al0.20Ga0.77N and other active regions. Single peaked and high efficiency ultraviolet (UV) emission at 345 nm from In0.03Al0.20Ga0.77N LEDs is achieved under continuous current injection conditions. Any significant broadening and peak shift of the electroluminescence (EL) spectrum were not observed. We attribute such a good properties to using of high quality InAlGaN-quaternary active layer. The EL intensity of the InAlGaN quaternary-based LED showed more one order of magnitude higher intensity than that of AlGaN and GaN based LEDs. Additionally, The I-L characteristics of the InAlGaN quaternary-based LED showed a linearly increasing of intensity with increasing of injection current density, that is also observed for InGaN based LEDs. This shows the recombination efficiency of the InAlGaNbased LED is as much as that of InGaN based LEDs. From these results InAlGaN quaternary is expected to be a promising material for UV LEDs and LDs.
INTRODUCTION III-nitrides are currently attracting a great interest for the application of visible or ultraviolet (UV) laser diodes (LDs) and light-emitting diodes (LEDs) [1]. Our goal is the development of UV LEDs and LDs working at wavelength of shorter than 360 nm. The application of these UV optical devices are high-density optical storage, high-efficiency lighting, chemical or medical apparatus, and disposal facilities for industrial wastewater. To date, InGaN based emitters operating in the visible or near UV wavelength range (λ>380 nm) have been commercially used. In order to obtain much shorter wavelength than that obtained from InGaN based emitters, AlGaN based UV devices should be developed. There are several reports on AlGaN-based UV devices [2-5] and InAlGaN based devices [6]. We achieved 333 nm of electroluminescence (EL) from Al0.03Ga0.97N/Al0.25Ga0.75N multi quantum well (MQW) LED with Mg-doped GaN/AlGaN SL hole conductive layers [5]. However, there are two serious problems in using AlGaN for the UV emitters. The first one is that the room-temperature emission intensity of AlGaN MQW is much weaker than that of InGaN MQW [7-9]. This is due to the high density of the threading dislocations. We proposed utilization of InAlGaN as the active layer, instead of AlGaN, because the emission intensity of InAlGaN is as strong as that of InGaN at room temperature [7]. The second one is the difficulty of current injection through the high Al composition (>30 %) AlGaN layer. Several groups reported that hole concentration in p-type layer is improved by using Mg-doped AlGaN/AlGaN or AlGaN/GaN superla
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