Luminescence properties of MOCVD grown Al0.2Ga0.8N layers implanted with Tb

Al_xGa_1-xN (x = 0.20) layers grown on (0001) sapphire substrates by metal organic chemical vapour deposition were implanted with terbium (Tb) ions at 150 keV with a fluence of 7 × 10¹⁴ Tb cm^-2 at different temperatures. After thermal annealing, all layers evidenced the Tb-related ⁵D₄-⁷F_J intra-4f⁸ transitions, demonstrating an enhancement of their intensity with increasing implantation temperature. A detailed spectroscopic analysis of the optical properties of these layers was conducted using luminescence techniques. An atypical behaviour for the relative intensity of both the broad visible band and the intraionic lines was found as a function of temperature and its origin is discussed based on potential fluctuation phenomena and energy transfer processes. The ⁵D₄-⁷F_J intra-4f⁸ transitions exhibit thermal population with increasing temperature between ∼100 K and ∼200-230 K, with a subsequent decrease up to RT due to further competitive non-radiative recombination paths. The values calculated for the population energies of each sample are in good agreement with the ones obtained for the activation energies of the de-excitation of the yellow broad band also present in the spectra, suggesting a correlation between the host defect de-excitation processes and the population of the ion emitting levels.