Abstract
Several distinct luminescent centres form in GaN samples doped with Eu. One centre, Eu2, recently identified as the isolated, substitutional Eu impurity, Eu sub(Ga, is dominant in ion-implanted samples annealed under very high pressures (1 GPa) of N) sub(2). According to structural determinations, such samples exhibit an essentially complete removal of lattice damage caused by the implantation process. A second centre, Eu1, probably comprising Eu sub(Ga in association with an intrinsic lattice defect, produces a more complex emission spectrum. In addition there are several unidentified features in the [super]5D) sub(0) to [super]7F sub(2 spectral region near 620 nm. We can readily distinguish Eu1 and Eu2 by their excitation spectra, in particular through their different sensitivities to above-gap and below-gap excitation. The present study extends recent work on photoluminescence/excitation (PL/E) spectroscopy of Eu1 and Eu2 to arrive at an understanding of these mechanisms in terms of residual optically active defect concentrations. We also report further on the 'host-independent' excitation mechanism that is active in the case of a prominent minority centre. The relevance of this work to the operation of the red GaN:Eu light-emitting diode is discussed.)