X-ray linear dichroism of defects in GaN:Mg using hard x-ray nanoprobe

Abstract

In this study, we report the application of synchrotron radiation nanoprobe techniques to the structural analysis of pyramidal defects in Mg doped GaN. A combination of fluorescence mapping with spectroscopic techniques enabled us to examine not only the elemental nature but also their crystallographic orientation on the submicron scale. Our observations provide strong evidence for the diffusion and subsequent segregation of background impurities of Fe and Cr on the sample surface, with the absence of pronounced sequential stacking compared with Ga atoms. The strong polarization-dependent x-ray absorption near-edge structure features showed the preservation of the hexagonal crystalline structure in both defect-free and hexagonal pyramids. From the spatially resolved x-ray linear dichroism, no preferential disorder was observed in the direction parallel or perpendicular to the crystal growth.

Status of the hard X-ray microprobe beamline ID22 of the European Synchrotron Radiation Facility

“…The investigated material is used for 10 Gb s À1 telecommunication applications up to 50 km propagation span. In the same way, the application of hard X-ray nanoprobe techniques to the structural analysis of pyramidal defects in Mg-doped GaN, a potential material for optoelectronic devices, has been recently reported (Martinez-Criado et al, 2009). Fig.…”

“…In this broad field, several scientific issues have been addressed using the beamline stations. The recent research comprises many materials with potential applications in spintronics, catalysis, optical sources, renewable materials like solid oxide fuel cell and silicon solar cells, etc (Sancho-Juan et al, 2011;Basile et al, 2010;Mino et al, 2010;Palancher et al, 2011;Kwapil et al, 2009;Martinez-Criado et al, 2009). For example, the combined use of micro-XRF, micro-XRD and nano-XRF techniques has been applied to the characterization of active-phase-coated metallic supports, structured catalysts, at different scales in both scanning and tomographic modes by Basile et al (2010).…”

Low-dimensional systems investigated by x-ray absorption spectroscopy: a selection of 2D, 1D and 0D cases

“…In the field of materials characterization, they are becoming a key tool for the space-resolved structural (micro-XRD) [391][392][393][394][395][396][397] and compositional (micro-XRF) [398][399][400] investigation of nano-structured or composite materials. There is also a great interest in performing XAS with high lateral resolution (micro-XAS) since it allows a new level of description of heterogeneous samples: indeed, combining microscopy with the atomic-scale structural information obtainable from XAS, the local atomic environment of single nanostructures can be determined [401][402][403][404][405][406][407][408][409][410][411] (see also Section 0). However, it is worth to underline that in the literature it is possible to find several micro-XANES studies [96,[412][413][414][415][416], where only few tens of eV are scanned across the edge, whereas papers reporting micro-EXAFS data, requiring an energy scan of several hundred of eV, are much more rare [123,[417][418][419][420][421].…”

Micro- and Nano-X-ray Beams

“…XANES and XLD collections around Ga atoms have shown tetrahedral coordination without significant local atomic distortion inside the hexagonal defects, providing direct evidence for the high short-range structural order [81]. The observations provided strong evidence for the diffusion and subsequent segregation of background impurities on these morphological defects.…”

“…Various pyramidal structures have been reported in GaN films grown by metaleorganic chemical vapor deposition (MOCVD). Recently, the use of synchrotron radiation nanoprobe techniques allowed a better understanding of the underlying structural process of three-dimensional Mg-rich hexagonal pyramids formed in MOCVD-grown GaN:Mg films [81]. So far, the origin is not completely understood, but it seems that the nucleation occurs at the sample surface, inducing changes in the stacking sequence from hexagonal to cubic structures or formation of Mg 3 N 2 precipitates [80].…”