Toyohashi, Japan--Researchers at Toyohashi University of Technology have created high-power red LEDs by codoping gallium nitride (Gan) with europium (Eu) and magnesium (Mg).1
Due to their sharp spectral line and high efficiency emission, Eu-doped nitride semiconductors show potential for novel optical devices such as low-threshold lasers and single-photon emitters. However, not all the Eu ions in the GaN host are incorporated in optically active sites that can be excited through the GaN. Therefore, it is important to develop methods to selectively incorporate Eu ions in higher-efficiency optical sites.
Hiroto Sekiguchi and colleagues at Toyohashi University of Technology and Hamamatsu Photonics (Hamamatsu City, Japan) have improved the emission intensity from Eu ions by Mg co-doping, and fabricated red LEDs with a Eu- and Mg-doped active layer grown by ammonia-source molecular-beam epitaxy (MBE).
The optimal Mg co-doping selectively enhanced a specific emission site and contributed to an increase in photoluminescence (PL) intensity of more than one order of magnitude. From the ratio of PL integrated intensity at 25 K to that at 300 K, the PL efficiency was determined to be as high as 77%. In the doped GaN based LEDs, clear rectification characteristics with a turn-on voltage of 3.2 V were observed and a pure red emission was observed by the naked eye at room temperature.
Source: Research highlight: http://www.tut.ac.jp/english/newsletter/research_highlights/research03.html#sec1
1. Hiroto Sekiguchi et al., Jpn. J. Appl. Phys. 52 (2013); DOI: 10.7567/JJAP.52.08JH01