Erbium location into AlN films as probed by spatial resolution experimental techniques

Abstract

This paper presents a thorough experimental investigation of erbium-doped aluminium nitride thin films prepared by R.F. magnetron sputtering, coupling Scanning Transmission Electron Microscopy X-ray-mapping imagery, conventional Transmission Electron Microscopy and X-ray diffraction. The study is an attempt of precise localisation of the rare earth atoms inside the films and in the hexagonal wü rtzite unit cell. The study shows that AlN:Er x is a solid solution even when x reaches 6 at.%, and does not lead to the precipitation of erbium rich phases. The X-ray diffraction measurements completed by simulation show that the main location of erbium in the AlN wü rtzite is the metal substitution site on the whole range. They also show that octahedral and tetrahedral sites of the wü rtzite do welcome Er ions over the [1.6-6%] range. The XRD deductions allow some interpretations on the theoretical mechanisms of the photoluminescence mechanisms and more specifically on their concentration quenching.

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

“…However, partial occupation of octahedral and/or tetrahedral insertion sites of the wurtzite structures by the Er atoms was also detected. 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 the variation in the Er concentration among the samples did not affect the average width of the columns, as has been verified by transmission electron microscopy cross section images. 5 The impact of the nanogranularity of the polycrystalline films on the EXAFS data is therefore expected to be limited, as grain size effects are generally important only for more distant shells than the first and the second ones and for cluster sizes smaller than 10 -15 nm. 8 More details on the morphological characterization of the samples studied here can be found elsewhere.…”

“…8 More details on the morphological characterization of the samples studied here can be found elsewhere. 5 Five samples were prepared with oxygen content limited to 5 -8 at.% with a variable average content of Er ranging from 0.5 to 3.6 at.%. All films were thermally treated post-deposition, employing conditions optimized to "activate" the luminescence (90 min at 950°C) as recommended in the literature.…”

“…5 In order to deepen our comprehension of the quenching, we present here a study of the local bonding configuration of the Er ion as a function of its concentration in AlNO. X-ray Absorption Fine Structure (XAFS) spectroscopy is an ideal technique for the study of the local bonding environment of rare earth dopants, as it does not necessitate long range order periodicity.…”

Ab initio investigation of the AlN:Er system

“…A variety of lanthanide elements in III-nitride semiconductors exhibit significant room temperature luminescence [1,2,3,4]. Hence, rare-earth (RE) doped nitrides are very promising for a series of optoelectronic applications among them flat panel displays and high contrast thick dielectric electroluminescent display devices [1,2].…”