Ab initio investigation of the AlN:Er system

Abstract

In the present study an ab initio investigation on the AlN:Er system for concentrations of Er ranging from 0.78 to 12.5 % is presented. The crystallographic localisation of the rare earth atoms in the wurtzite lattice is determined, elucidating previously published experimental deductions, and the existence of a solid solution in the AlN:Er system in this range is confirmed.Er incorporation in the tetrahedral and octahedral insertion sites is shown to be thermodynamically metastable and is found to induce shallow states in the bandgaps. The effect of Er concentration on the lattice constants and bandgaps and bandstructures of the ErxAl1-xN ternary compound is presented. Finally, in accordance with experimental specifications, Er incorporation in the AlNO system is also examined.

Extended X-ray absorption fine structure study of the Er bonding in AlNO:Erx films with x ≤ 3.6%

“…Many compounds doped with rare earths (RE) are subject to RE nanoprecipitation partly responsible for concentration quenching. Whereas previous experimental investigations and DFT calculations on our system 17 suggests that no precipitation occurs, the EXAFS study presented here allows us to draw stronger conclusions on that point. No Er-rich clusters such as ErN or Er 2 O 3 were detected by XAFS.…”

“…For Er located in wurtzite structural voids and in Al substitutional sites, the relaxed positions, obtained by DFT calculations published in a comprehensive work by our colleagues, were taken into account. 17 The Fourier transform amplitudes of the theoretical k 3 -weighted (k) spectra, obtained using the above mentioned models, are compared with the experimental spectrum of the AlNO film that contains 2.8% Er in Fig. 3.…”

“…%. 17 These results also imply that XRD detexturation results 5 obtained on the same thin films need re-examination: the exploitation of relative intensities of the peaks to conclude about the relative distribution of Er in insertion sites of wurtzite has to be reconsidered. It then appears that, as already encountered in other thin films adopting the hexagonal ZnO structure such as ZnSnN 2 30 or ZnGeN 2 31 , the simple hexagonal unit cell is not sufficient.…”

“…17 The Fourier transform amplitudes of the theoretical k 3 -weighted (k) spectra, obtained using the above mentioned models, are compared with the experimental spectrum of the AlNO film that contains 2.8% Er in Fig. 3.…”

“…5 Furthermore, calculations performed using Density Functional Theory (DFT) predicted that the rare earth atoms are distributed throughout the lattice and do not agglomerate, and confirmed the main occupation of Er in the Al sites, with much lower occupancies of insertion sites (octahedral and to a lesser extent tetrahedral). 17 Therefore, the crystallographic model that was used in the analysis of the EXAFS spectra was wurtzite AlN (space group P63mc), where Er substitutes for Al. It should be pointed out that in addition to this substitutional model, the following models were also considered:…”