Gallium clustering and structural effects of hydrogenation in InGaN/GaN nanostructures

Abstract

We addressed the issue of atomic ordering in a series of In-rich InxGa1−xN epilayers grown on a GaN/AlN/sapphire(0001) epitaxial template by quantitatively measuring the Ga-cation coordination in the second atomic shell of Ga. We used Diffraction Anomalous Fine Structure Spectroscopy (DAFS) at the Ga K-edge to select the signal coming from the Ga atoms in the epilayer and eliminate any contribution from the buffer layer. DAFS measurements were also performed on hydrogenated epilayers in order to investigate the possible formation of Ga-H complexes. We find that deviation from cation random distribution in the form of Ga clustering is present in both untreated and hydrogenated samples and that in the latter ones the second atomic shell around Ga is modified, suggesting an additional perturbation of the cation sublattice related to hydrogen. However, comparing the present results with In K-edge x-ray absorption spectra previously reported, we conclude that the formation of Ga-H complexes vs. In-H ones is unlikely. Cation clustering has to be anyway taken into account as a possible channel playing in the determination of the optical bandgap of these technology-oriented semiconductors.

Exceptional Hydrogen Uptake in Crystalline InxGa1–xN Semiconductors

“…As for the untreated epilayers (two bottommost spectra), they are better reproduced by an ab initio simulation with a slightly higher In content ( x = 0.80 instead of x = 0.70 or x = 0.60). This is probably due to the effects of In clustering, previously observed in these alloys. , Regarding the x = 0.74 and x = 0.62 samples hydrogenated at the highest dose d H = 10 18 ions cm –2 (upper part of the figure), from 20% to 25% of In* is necessary to account for all the spectral modifications (disappearance of the prepeak 1 and smoothing of features 2, 3 and 4. )…”

“…The effects of HBC-3Hab complexes on the local structural properties of In x Ga 1−x N have been already addressed via In Kedge X-ray absorption spectroscopy (XAS) 8 and Ga K-edge diffraction anomalous fine structure spectroscopy (DAFS). 11 However, the presence of the complexes could only be detected indirectly, looking at the broadening of the interatomic distance distribution in the cation sublattice: this did not allow us to make an experimental estimation of the complex concentration. Nonetheless, the HBC-3Hab complex is surprisingly stable thanks to local strain reduction, and solitary cation theory 10 predicts a high concentration of HBC-3Hab complexes in InN, which may make XAS directly sensitive to H in In-rich alloys.…”

Unravelling the Local Crystallographic Structure of Ferromagnetic Ga$_y$Fe$_{4-y}$N Nanocrystals Embedded in GaN

“…The quantitative analysis of the data, which has been performed following the approach described in Refs. [23][24][25], and the resulting structural parameters are collected in Table II. For sample S1, the weakness of the fine structure signal does not allow a reliable quantitative analysis.…”

FORTE – a multipurpose high-vacuum diffractometer for tender X-ray diffraction and spectroscopy at the SIRIUS beamline of Synchrotron SOLEIL

“…In parallel with tender XRD and DAFS, the FORTE diffractometer can also be used for XAS experiments in the same energy range, thanks to the four-element SDD described in Section 3, which allows measurement of even ultra high dilute systems. In some cases, when the sample geometry and Bragg angles at play allow it and self-absorption is not an issue, XAS measurements can also be performed simultaneously to DAFS resulting in time saving (Ciatto et al, 2018). In other cases, it may be interesting to choose a specific incidence angle for the XAS measurements; this is often a requirement in experiments on nanostructures, where confining the X-ray probe in a near-surface region using a subcritical grazing angle allows reduction of the signal background generated from fluorescence lines originating from the substrate or buffer layers.…”

“…In parallel with tender XRD and DAFS, the FORTE diffractometer can also be used for XAS experiments in the same energy range, thanks to the four-element SDD described in Section 3, which allows measurement of even ultra high dilute systems. In some cases, when the sample geometry and Bragg angles at play allow it and self-absorption is not an issue, XAS measurements can also be performed simultaneously to DAFS resulting in time saving (Ciatto et al, 2018).…”