GaN quantum dot UV light emitting diode
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GaN quantum dot UV light emitting diode Jeong-Sik Lee2, Satoru Tanaka1, Peter Ramvall2, and Hiroaki Okagawa3 1 Research Institute for Electronic Science, Hokkaido University, Kita 12 Nishi 6 Kita-ku Sapporo 060-0812, Japan 2 Research and Development Center, Nippon EMC, 2008-2 Wada Tama-shi Tokyo 205-0001, Japan 3 Photonics Laboratory, Mitsubishi Cable Industries, 4-3 Ikejiri Itami-shi Hyogo 664-0027, Japan ABSTRACT The fabrication and evaluation of a UV light-emitting diode (LED) incorporating GaN quantum dots as the active layer is demonstrated. The GaN quantum dots were fabricated on an AlxGa1-xN (x~0.1) surface using Si as an antisurfactant. Exposing the AlxGa1-xN surface to the Si antisurfactant prior to GaN growth enabled the formation of quantum dots on a surface where growth by the Stranski-Krastanov mode would not be possible. A fairly high density of dots (1010-1011 cm-2) with controllable dot sizes was achieved. Room temperature luminescence at 360 nm was clearly observed during current injection (cw) into an LED structure including the GaN quantum dots. The origin of the electroluminescence is discussed by comparing it to photoluminescence measurements. INTRODUCTION Optical devices operating in the UV region are becoming increasingly important due to possible future applications in white light-emitting diodes (LEDs), high density versatile disks, medical and environmental tools, etc. White LEDs are especially interesting as replacements for conventional fluorescent lamps, due to their inherent advantages in terms of increased lifetime, higher reliability, environmental issues, etc. Blue and violet LEDs, laser diodes (LDs) and recently white LEDs are already commercially available, based on active layers of the ternary alloy InGaN. The radiative recombination rate of InGaN layers has been found to be unexpectedly high, possibly because of quantum dot-like features induced by local compositional fluctuations [1,2]. Several attempts have been made to manufacture UV LEDs mainly by lowering the In content in InGaN quantum wells (QWs). However, by this approach the external quantum efficiency drastically decreases with reduced In fraction. The reason for this might be a lack of localized states in the InGaN QWs. Research into quantum dots (QD) in nitride semiconductors is attracting a lot of attention, not only because of their unique optical properties [3] but also for device applications. Tanaka et al. [4] have demonstrated GaN QD growth on AlxGa1-xN (x~0.15) surfaces using a Si antisurfactant, which was found to change the mode of GaN growth from step-flow to threedimensional. In addition to fundamental studies, including investigations into the growth mechanisms [5,6] and optical properties [7], preliminary results have been reported [8] that demonstrate stimulated emission from GaN QDs by optically pumping them, which opens the possibility of making GaN QD laser diodes. Device structures grown using this antisurfactant method have advantages in terms of current injection into the QDs, compared with
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