Eu-doped GaN (GaN:Eu) is a promising material for the active layer in nitride-based red light-emitting diodes (LEDs). Recently, we have demonstrated the first GaN:Eu-based red LED operating at low voltage. However, for practical applications it is necessary to improve the light output. One method for enhancing the luminescence output is to increase the concentration of Eu ions. However, for normal growth temperatures and high Eu concentrations, the formation of precipitation on the sample surface was observed. In this contribution, we will discuss the properties of the Eu precipitation and demonstrate how lowering the growth temperature can reduce it.
For GaN:Eu samples grown at lower temperatures, mirror-like surface with no precipitations was obtained and the room-temperature photoluminescence intensity was approximately doubled as compared to samples grown at the standard temperature. In general, lowering the growth temperature of GaN is considered to increase the defect density. We propose a model that explains how this can lead to the improvement of output intensity. It appears that Eu ions can recover the quality of the grown crystal, while defects around Eu ions can mediate energy transfer from the host. In addition, low-temperature photoluminescence of these samples showed some features which can be explained by the reconfiguration of Eu centers.