Present understanding of Eu luminescent centers in Eu-doped GaN grown by organometallic vapor phase epitaxy

Abstract

We have succeeded in growing Eu-doped GaN (GaN:Eu) layers with high crystalline quality by organometallic vapor phase epitaxy, and have demonstrated a low-voltage current-injected red emission from a light-emitting diode (LED) using the GaN:Eu layer with an applied voltage of as low as 3 V. By optimizing growth conditions and device structures, the light output power has increased steadily to up to sub-mW at an injected current of 20 mA. For further improvement of the output power, Eu luminescent centers have been spectroscopically investigated in GaN:Eu. A variety of Eu luminescent sites and a strongly site-dependent energy transfer process were clearly revealed. The energy-transfer efficiency was markedly enhanced by codoping of Mg with Eu. A proposed model for centers with high energy-transfer efficiencies is discussed in relation to the local structure.