Efficient luminescence from rare-earth elements by nitride-based nano-particle

Abstract

We have succeeded in the growth of europium (Eu)-doped GaN layer grown by organometallic vapor-phase epitaxy (OMVPE) and demonstrated the first low-voltage operation of current-injected red emission from a p-type/Eu-doped/n-type GaN light-emitting diode (LED) at room temperature. In order to clarify the growth characteristics, we investigated the growth temperature dependence of luminescence properties. The dominant photoluminescence (PL) peak intensity at 621 nm, due to the intra-4f shell transitions of ⁵D0-⁷F₂ in Eu³⁺ ions, became the highest when the sample was grown at 1000℃. Above 1000℃, the PL peak intensity decreased because of the lower Eu concentration associated with the surface desorption of Eu³⁺ ions. On the other hand, although the Eu concentration of the layer grown at 900℃ was only half of the layer grown at 1000℃ , the pronounced decline in the PL peak intensity was observed with decreasing growth temperature from 1000 to 900℃, which results from the modification of the local structure around Eu³⁺ ions. These results indicate that the growth temperature strongly influences the Eu concentration and the local structure around Eu³⁺ ions. Therefore, an optimized growth temperature exists for strong Eu-related luminescence from Eu-doped GaN layer grown by OMVPE. As for an electronic device, the bright red emission was obtained with an applied voltage as low as 3V under normal lighting conditions. At a d.c. current of 20 mA, the output power, integrated over the ⁵D0-⁷F₂ transition of Eu³⁺ ions (around 621 nm), was 1.3 μW. This result suggests a novel way to realize GaN-based red LEDs and monolithic devices comprising red, green and blue GaN-based LEDs.