Current Injection UV-Emission from InAlGaN Multi-Quantum-Well Light-Emitting Diodes
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Current Injection UV-Emission from InAlGaN Multi-Quantum-Well Light-Emitting Diodes A. Kinoshita1 2, H. Hirayama1, M. Ainoya1 2, J. S. Kim1, A. Hirata2 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 InAlGaN quaternary material is very attractive for realizing ultraviolet (UV) emitting devices working at 300 – 350 nm wavelength range. We demonstrate current injection into 340 nm-band InAlGaN based UV light emitting diodes (LEDs), for the first time, fabricated by metal organic vapor phase epitaxy (MOVPE). We performed current injection into AlGaN/AlGaN multi quantum well (MQW), bulk InAlGaN quaternary and InAlGaN/InAlGaN MQW LEDs through Mg-doped AlGaN/GaN superlattice hole conductive layers. The injected current density was ranging 0 – 0.5 kA/cm2 under pulsed or CW operation. The intensity of both photoluminescence (PL) and electroluminescence for InAlGaN quaternary-based LED was much higher than that for AlGaN based LEDs at room temperature. From these results InAlGaN quaternary-based QWs are expected to realize high intensity UV LEDs and LDs.
INTRODUCTION III-nitrides are currently attracting 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. The applications of the UV optical devices include high-density optical storage, high-efficiency lighting, chemical or medical apparatus, and disposal facilities for industrial waste water [2]. 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 [3, 4]. 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 [6]. 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 superlattice (SL) structures [8, 9]. We also confirmed that vertical hole conductivity of SL hole conductive layer is improved and achieved current injection emission of 330 nm band from AlGaN MQW using the SL hole conducting G12.6.1
layers [10]. Recently, we achieved highly p-type doping into wide band gap AlGaN by incorporati
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