Optical investigations of europium ion implanted in nitride-based diode structures

Abstract

AlGaN/GaN-superlattice based diode structures under study were grown by metal organic chemical vapour deposition, then implanted with two different Eu ion beam fluences, and further submitted to high temperature and high pressure thermal annealing treatments. The effects of Eu implantation and annealing on the diode structure emission characteristics were investigated at 14 K and room temperature. Eu3+ luminescence was observed in both Eu-implanted and annealed samples, being the most intense emission assigned to the 5D0 → 7F2 transition in the red spectral region (~621 nm), in line with the main observed behaviour of Eu3+ ions implanted in GaN layers. The combined excitation/emission spectra revealed that the measured intraionic emission corresponds to an overlap of two principal emitting centres which can be excited through above and below GaN bandgap. In addition, a considerable reduction of the non-radiative channels was observed for the diode structure implanted with the highest Eu fluence, inducing a higher thermal stability of the intra-4f6 lines intensity. In contrast to GaN layers, the perceived Eu3+ red emission observed at room temperature was found to be strongly sensitive to the GaN above bandgap excitation (out of the resonance conditions) suggesting that additional energy transfer between the AlGaN/GaN superlattice excitons and the Eu3+ ions occurs, therefore widening the excitation pathways for the red luminescence.