High-concentration doping of Eu ions working as luminescent centers in GaN is required to improve light output of optical devices. GaN nanocolumns can be used to achieve high crystallinity in high-concentration Eudoped GaN (GaN:Eu). In this study, optical properties of a GaN:Eu nanocolumn grown by RF-plasma-assisted molecular-beam epitaxy (RF-MBE) are investigated and GaN:Eu nanocolumn light-emitting diodes (LEDs) are demonstrated. Suppression of yellow luminescence and concentration quenching of PL intensity are observed at RT for GaN:Eu nanocolumns. When the effect of Eu concentration on optical properties is analyzed using rate equation, an increase in the Eu concentration is observed to affect 5 D 0 lifetime corresponding to back transfer, and not the effective cross-section corresponding to transfer efficiency. Based on these results, GaN:Eu nanocolumn LEDs are fabricated on an n-type (111) Si substrate. Clear rectification characteristics and sharp red luminescence are observed. The light output increases with increasing Eu concentration up to a concentration of 6 Â 10 20 cm À3 . These results suggested that GaN:Eu nanocolumns provide feasible crystal to realize novel optical devices.

For the first time, a rare‐earth‐doped GaN nanocolumn light‐emitting diode is fabricated on an n‐type (111) Si substrate, grown by rf‐plasma‐assisted molecular beam epitaxy. The nanocolumn structure remained in the n‐GaN and europium‐doped GaN active regions, but the lateral growth was enhanced in the p‐GaN region such that a continuous film was obtained. Clear diode characteristics and a sharp red luminescence with two dominant peaks at 620.3 and 633.8 nm were observed at room temperature. The shift in the wavelength with an increase in the injected current was <0.2 nm. Thus, this device has the potential for application as a stable‐wavelength optical device.