Preferential formation of highly efficient Eu luminescent centers in Eu-doped GaN grown on semipolar (202¯1) GaN

Eu-doped GaN (GaN:Eu) exhibiting bright red emission is a promising material for the realization of ultrahigh-resolution micro-light-emitting diode (LED) displays that can be applied to virtual reality/augmented reality/mixed reality. The full-color monolithic integration of a red GaN:Eu LED and blue/green InGaN LEDs is a key technology, in which the use of semipolar substrates is preferred to suppress wavelength shift in the InGaN LEDs under current injections. We investigate the effects of the growth plane on GaN:Eu-based red emission and find that the emission intensity from a semipolar (202¯1) GaN:Eu is drastically enhanced as compared with a conventional (0001) GaN:Eu,O. Combined excitation–emission spectroscopy reveals that the fraction of Eu luminescent centers with different local structures dramatically changed. A highly efficient Eu center is preferentially formed, and its abundance increases by more than two orders. These results show a clear pathway to develop a red LED with higher light output power.