Multiple optical centers in Eu-implanted AlN nanowires for solid-state lighting applications

Abstract

A detailed spectroscopic analysis of Eu3+ implanted and annealed AlN nanowires (NWs) grown by plasma-assisted molecular beam epitaxy is presented by using micro-Raman, temperature-dependent steady-state photoluminescence, and time-resolved photoluminescence. Two different annealing temperatures (1000 °C and 1200 °C) were used. Such annealing conditions achieved a recovery of the original AlN crystalline structure as confirmed by Raman analysis. For both samples, the red Eu3+ intra-4f 6 luminescence was demonstrated, where the 5D0 → 7F2 transition at 624 nm is the most intense. Two well-resolved Eu optically active centers were observed in the present AlN NWs and designated as Eu1 and Eu2, due to their similar spectral shape when compared to those observed in GaN layers [Bodiou et al., Opt. Mater. 28, 780 (2006); Roqan et al., Phys. Rev. B 81, 085209 (2010)]. Their behavior was found to depend on the annealing temperature. Photoluminescence studies reveal that at 14 K, Eu2 is dominant for the lower annealing temperature, while Eu1 is dominant for the highest annealing temperature. Moreover, at room temperature, Eu1 center was found to be the dominant for both samples. Indeed, the luminescence intensity of the 5D0 → 7F2 transition exhibits a lower thermal quenching for the samples annealed at the highest temperature (∼80% for the sample annealed at 1200 °C and ∼50% for the sample annealed at 1000 °C) boosting their potential use as efficient red emitters.