Electroluminescence Properties of Eu-doped GaN-based Light-emitting Diodes Grown by Organometallic Vapor Phase Epitaxy
- PDF / 297,749 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 92 Downloads / 194 Views
Electroluminescence Properties of Eu-doped GaN-based Light-emitting Diodes Grown by Organometallic Vapor Phase Epitaxy Atsushi Nishikawa, Naoki Furukawa, Dong-gun Lee, Kosuke Kawabata, Takanori Matsuno, Yoshikazu Terai and Yasufumi Fujiwara Division of Materials and Manufacturing Science, Graduate School of Engineering,Osaka Universtiy, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
ABSTRACT We investigated the electroluminescence (EL) properties of Eu-doped GaN-based lightemitting diodes (LEDs) grown by organometallic vapor phase epitaxy (OMVPE). The thickness of the active layer was varied to increase the light output power. With increasing the active layer thickness, the light output power monotonically increased. The maximum light output power of 50 μW was obtained for an active layer thickness of 900 nm with an injected current of 20 mA, which is the highest value ever reported. The corresponding external quantum efficiency was 0.12%. The applied voltage for the LED operation also increased with the active layer thickness due to an increase in the resistance of the LED. Therefore, in terms of power efficiency, the optimized active layer thickness was around 600 nm. These results indicate that the optimization of the LED structure would effectively improve the luminescence properties. INTRODUCTION Eu-doped GaN is expected to realize a GaN-based red LED, which is a key technology for fabrication of the monolithic devices, composed of red, green and blue GaN-based LEDs for full-color display or lighting technology [1, 2]. In order to realize the GaN-based red emission, the fabrication of Eu-doped GaN layers has mainly been performed by ion implantation with post-thermal annealing or molecular-beam epitaxy [3-7]. However, it is rather difficult to obtain a current-injected red emission from a Eu-doped GaN layer fabricated by those methods because of the difficulty in the consecutive growth of high-quality p-n junction structure with the Eudoped GaN layer. Owing to the successful growth of Eu-doped GaN by OMVPE, we have demonstrated the first current-injected operation of a Eu-doped GaN-based red LED at room temperature (RT) [8, 9]. We have also reported improved luminescence properties with a light output power being as high as 17 μW for the Eu-doped GaN-based red LED grown at atmospheric pressure [10-12]. Although the remarkable improvement was observed in the light output power, it is still insufficient from a practical point of view. The Eu concentrations of the previous studies are under 1020 cm-3, where the luminescence intensity still increases with
9
increasing Eu concentration without concentration quenching of the luminescence intensity. Therefore, the number of Eu ions in the active layer should be increased in order to improve the luminescence intensity. It is inevitable to optimize the LED structure as well as to clarify the properties of the Eu-doped GaN active layer. In this study, we investigated the EL properties of Eu-doped GaN-based LEDs with different active layer thicknesses. EXPERIMENT The sa
Data Loading...
