Europium (Eu) doped nitride semiconductors make it possible to create novel optical devices, such as a low threshold lasers and single photon emitters. However, not all europium ions are incorporated in semiconductor optical active site that can be excited through the GaN host. Therefore, it is important to develop methods to selectively incorporate europium ions in higher-efficiency optical sites.

Hiroto Sekiguchi and his colleagues at Toyohashi University of Technology and Hamamatsu Photonics Ltd have improved the emission intensity from europium ions by magnesium co-doping and fabricated red LEDs with europium and magnesium doped active layer grown by ammonia source MBE.

The optimal magnesium co-doping selectively enhanced a specific emission site and contributed to a photoluminescence (PL) intensity increase 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 %.

On the basis of these results, europium doped GaN based LEDs were fabricated. 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. These results suggest that europium and magnesium doped GaN is expected to be utilised for realising new nitride-based light-emitting devices.

This work has been described in the paper, "Red-Light-Emitting Diodes with Site-Selective Eu-Doped GaN Active Layer," by H Sekiguchi et al in Japanese Journal of Applied Physics.