Local Crystal Field Analysis of Eu(3+) and Er(3+) Ions in a Wide Band Gap Semi-Conductor GaN

摘要

From time resolved and site-selective excitation spectroscopy, three sites have been identified for Er(3+) ions in GaN. The main center was ascribed to Er(3+) ions substituted on the Ga sub-lattice, the two others assigned to Er(3+) complexes in interstitial positions. The complex decay profile of the (4) S(3/2) fluorescence of the main center and its concentration dependence indicate the occurrence of energy transfers between adjacent Er(3+) ions. The fluorescent transients were modeled using a diffusion-limited model and the microscopic parameters of the interaction determined. The processes involved in the filling of the infrared emitting level have been identified and suggest a strong interaction between Er(3+) in interstitial positions and defects nearby. The quenching of the infrared luminescence of the main center is due to a similar diffusion-limited process. The quantum efficiency (QE) of the infrared emission was evaluated and its reduction explained by interaction with free carriers. The crystal field parameter calculated for the main center confirms the substitution of the rare earth in the semiconductor phase excluding oxygen environment This is supported by the covalent character of the bounding of Er(3+) to nitrogen in GaN. Three sites were also found for Eu(3+) ions in GaN. The energy of the Stark components of several levels were determined. The very low energy values compared to that obtained in insulators confirm the strong nephelauxetic effect in GaN due to covalent bonding RE-N. From the scalar crystal field parameter, one Eu(3+) center has been related to the Er(3+) main center.