Modification of Eu incorporation sites by the dissociation of hydrogen defect complexes In Mg and Eu Co-doped gallium nitride

Summary form only given. The success of GaN-based lasers and LED devices is based on the ability to activate magnesium ions as acceptors. The initial failures in p-doping stems fro m the role of hydrogen that is present in samples grown by metal-organic chemical vapor deposition (MOCVD) which passivates the Mg ions through the formation of stable Mg-H-N complexes. The breakthrough came with the discovery that proper thermal annealing and low electron beam irradiation (LEEBI) were effective in breaking up these complexes and activating the Mg acceptors [1,2]. There is mounting evidence that hydrogen plays a simila r decisive role in the realization of electrically-pumped rare-earth based light emitters in GaN. The addition of Mg in OMVPE-grown Eu:Mg co-doped GaN samples introduce four new sites or incorporation environments, labeled Mg 1-4, caused by the perturbation of passivated Mg-H complexes. These new sites are very efficient in capturing the energy from electron-hole pairs leading to strong luminescence in the red spectral area. However, we find that the cathodoluminescence (CL) intensity of the Mg4 site decreases strongly under electron beam exposure at 30K. To further study this effect, we developed a confocal microscope stage that fits into an SEM, allowing for simultaneous CL and site selective photoluminescence (PL) studies. Performing, in this instrument, combined excitation emission spectroscopy before and after electron beam irradiation, we can exclude any influence from the excitation pathway on the emission. We find that the changes induced by the electron beam exposure are due to a conversion of the Mg4 centers into a site that very closely resembles Eu1 which dominated the resonantly excited PL spectra in the absence of Mg-doping. Similar to what has been proposed for the Mg-H complexes in the absence on Eu doping, we suggest that the hydrogen can migrate within the vicinity of the Eu ion to a nearest neighbor trap eventually moving far enough away- that the perturbation is removed, but the excitation efficiency remains [3]. We further studied the temperature dependence of the site conversion process and the stability of the created center configurations. We find that the conversion is most efficient at temperatures below 60K. Above this temperature, thermally induced mobility of the hydrogen reduces the conversion efficiency and leads to a reversal of the effect in the absence of the electron beam once the sample is heated up. On the other hand, the smaller conversion that can be achieved at room temperature remains stable. In summary, using a newly developed setup we were able to track the migration of hydrogen atoms under LEEBI using Eu atoms as a probe. This process was found to be dependent on temperature and irradiation power. The stability of the migration was also seen to have a dependence on the temperature of irradiation under temperature cycling.