A Methodological Study of the Best Solution for Generating White Light Using Nitride-Based Light-Emitting Diodes

Autor: Motokazu Yamada, Yukio Narukawa, Takashi Mukai, Yoshinori Murazaki, Hiroto Tamaki
Rok vydání: 2005
Předmět:
Zdroj: IEICE Transactions on Electronics. :1860-1871
ISSN: 1745-1353
0916-8524
Popis: In search of suitable white-LED for general illumination, we fabricated various types of white-LEDs using different methods. As the first method, we used the multichip method in which multiple emitters were mounted in one package. This type showed a good general color-rendering index (Ra) = 90 by the optimizing the emission wavelength of each LED chip. However, the electric driving circuitry was too complex for use in general illumination. Secondly, we used a monolithic white-LED by using the multicolor emitting multiple-quantum well (MQW) for the active layers, which consisted of quantum wells (QWs) with different In compositions. A high Ra = 80.1 was obtained in the three-color-emitting white-LED but the luminous efficacy (η L ) was only 8.11 1m/W. As the third method, we used the color conversion method using phosphors. We fabricated a white-LED which consisted of a near-UV-LED chip and blue/yellow phosphors in order to improve the luminous efficacy of the white-LED under high forward-bias current. At 100 mA, the luminous flux (I L ) was estimated to be 7.61m. However, this white-LED degraded quickly, because the epoxy resin used for package was the general purpose one and deteriorated under the UV-light from the n-UV-LED. Next, we improved the Ra and η L of a traditional white-LED which consisted of blue-LED chip and yellow phosphor. In order to improve the Ra, we added a newly developed red phosphor. We obtained a Ra = 87.7 at low-color-temperature. Then, in order to improve the efficiency of the white-LED, we improved the extraction efficiency (η EX ) of the blue-LED by using a patterned sapphire substrate and a high reflection Rh-mesh-patterned p-electrode. Then, we obtained a 62.0 1m/W at 20 mA. As a result, we concluded that the color conversion method of using a blue-LED for general illumination has advantages in efficiency, color-rendering, cost and lifetime. It also has simpler electric driving circuitry.
Databáze: OpenAIRE
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