Optically active centers in Eu implanted, Eu in situ doped GaN, and Eu doped GaN quantum dots

Abstract

A comparison is presented between Eu implanted and Eu in situ doped GaN thin films showing that two predominant Eu sites are optically active around 620 nm in both types of samples with below and above bandgap excitation. One of these sites, identified as a Ga substitutional site, is common to both types of Eu doped GaN samples despite the difference in the GaN film growth method and in the doping technique. High-resolution photoluminescence (PL) spectra under resonant excitation reveal that in all samples these two host-sensitized sites are in small amount compared to the majority of Eu ions which occupy isolated Ga substitutional sites and thus cannot be excited through the GaN host. The relative concentrations of the two predominant host-sensitized Eu sites are strongly affected by the annealing temperature for Eu implanted samples and by the group III element time opening in the molecular beam epitaxy growth. Red luminescence decay characteristics for the two Eu sites reveal different excitation paths. PL dynamics under above bandgap excitation indicate that Eu ions occupying a Ga substitutional site are either excited directly into the D50 level or into higher excited levels such as D51, while Eu ions sitting in the other site are only directly excited into the D50 level. These differences are discussed in terms of the spectral overlap between the emission band of a nearby bound exciton and the absorption bands of Eu ions. The study of Eu doped GaN quantum dots reveals the existence of only one type of Eu site under above bandgap excitation, with Eu PL dynamics features similar to Eu ions in Ga substitutional sites.

Sequential multiple‐step europium ion implantation and annealing of GaN

“…This centre has been recently reported in in situ Eu/Mg co-doped MOCVD GaN [20] and an interesting temperature-hysteretic behaviour of this centre, named Eu0, in implanted samples was discussed in terms of a charge-transfer involving the shallow-deep instability of the Mg acceptor [21]. Our results show that the high nitrogen pressure and/or the longer annealing time play an important role in the formation of this Eu0 centre since it occurs, albeit very weakly, for HTHP annealing at 1100 ºC while for low pressure RTA at the same temperature the known Eu1 and Eu2 centres [12,22] with main emission lines at ~ 622 nm, are dominant. 4 Conclusions Sequential multiple low fluence Eu ion implantations, each followed by an RTA step at 1000 ºC were performed on high quality MOCVD GaN and medium quality HVPE GaN:Mg samples.…”

Functionalizing self-assembled GaN quantum dot superlattices by Eu-implantation

“…29,30 Furthermore, Eu 3+ ions are known to give rise to multiple active centers in the binary systems. 31,32 In this context, it is important to emphasize the difference of the lattice site location of Eu ͑Eu is known to be incorporated into near-substitutional Ga and Al sites in GaN and AlN, respectively 25,26 ͒ and the different optically active centers ͑often also called "sites"͒ which depend on the local symmetry around the substitutional Eu ͑which can for example be influenced by next neighbor defects͒. Figure 7 presents the PL spectra showing the main 5 D 0 → 7 F 2 transition excited using the 325 nm laser line of all SL samples as well as GaN, AlN, and Al 0.5 Ga 0.5 N epilayers implanted with 1 ϫ 10 15 cm −2 and annealed.…”

Lattice site location of optical centers in GaN:Eu light emitting diode material grown by organometallic vapor phase epitaxy

“…Euimplanted GaN typically shows two majority optical centers named Eu1 and Eu2. 14,15 The latter was recently identified as the isolated substitutional Eu Ga impurity. 7 In general, both Eu1 and Eu2 are excited by above band gap light while Eu1 is additionally excited by a broad absorption feature below the band gap of GaN.…”