Enhanced light output of Eu, O-codoped GaN caused by reconfiguration of luminescent sites during post-growth thermal annealing

Abstract

Luminescence efficiency of Eu-related emission from Eu, O-codoped GaN (GaN:Eu, O) strongly depends on the local structure of Eu ions. Growth at relatively low temperature (∼960 °C) not only enables high Eu doping concentration but also elevates Eu-clustering due to its low diffusion coefficient, which results in formation of a large number of inefficient luminescent sites. We have studied the impact of post-growth thermal annealing at high temperatures on elimination of Eu clusters by photoluminescence measurements. These clarify that thermal annealing at high temperatures induces changes in the structural conformation and converts inefficient luminescent sites to efficient ones. As a result, the sample annealed at 1100 °C shows increased luminescence efficiency with a maximum of 5.1 times that of the as-grown sample. Post-growth thermal annealing offers a way to improve the efficiency of GaN:Eu, O further for practical application in III-nitride-based monolithic three-primary colors' light-emitting diodes.