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Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS	Extended X-ray absorption fine structure study of the Er bonding in AlNO:Er x films with x ≤ 3.6% M. Katsikini , V. Kachkanov , P. Boulet , P. R. Edwards , K. P. O'Donnell , V. Brien Journal Of Applied Physics 124 DOI: 10.1063/1.5036614 Diamond Proposal Number(s): [9370] Show Abstract ▼ Abstract: The structural properties of Er-doped AlNO epilayers grown by radio frequency magnetron sputtering were studied by Extended X-ray Absorption Fine Structure spectra recorded at the Er L3 edge. The analysis revealed that Er substitutes for Al in all the studied samples, and the increase in the Er concentration from 0.5 to 3.6 at. % is not accompanied by the formation of ErN, Er2O3, or Er clusters. Simultaneously recorded X-ray Absorption Near Edge Structure spectra verify that the bonding configuration of Er is similar in all studied samples. The Er-N distance is constant at 2.18–2.19 Å, i.e., approximately 15% larger than the Al-N bond length, revealing that the introduction of Er in the cation sublattice causes a considerable local distortion. The Debye-Waller factor, which measures the static disorder of the second nearest shell of Al neighbors, has a local minimum for the sample containing 1% Er that coincides with the highest photoluminescence efficiency of the sample set.	Aug 2018
B16-Test Beamline	Structural dynamics of GaN microcrystals in evolutionary selection selective area growth probed by X-ray microdiffraction V. Kachkanov , B. Leung , J. Song , Y. Zhang , M.-C. Tsai , G. Yuan , J. Han , K. P. O'Donnell Scientific Reports 4 DOI: 10.1038/srep04651 PMID: 24722064 Open Access Show Abstract ▼ Abstract: A method to grow high quality, single crystalline semiconductor material irrespective of the substrate would allow a cost-effective improvement to functionality and performance of optoelectronic devices. Recently, a novel type of substrate-insensitive growth process called Evolutionary Selection Selective Area Growth (ES-SAG) has been proposed. Here we report the use of X-ray microdiffraction to study the structural properties of GaN microcrystals grown by ES-SAG. Utilizing high resolution in both direct and reciprocal spaces, we have unraveled structural dynamics of GaN microcrystals in growth structures of different dimensions. It has been found that the geometric proportions of the growth constrictions play an important role: 2.6 mm and 4.5 mm wide growth tunnels favor the evolutionary selection mechanism, contrary to the case of 8.6 mm growth tunnels. It was also found that GaN microcrystal ensembles are dominated by slight tensile strain irrespective of growth tunnel shape.	Apr 2014
B16-Test Beamline	Characterisation of III-nitride materials by synchrotron X-ray microdiffraction reciprocal space mapping Vyacheslav Kachkanov , Igor Dolbnya , Kevin O'Donnell , Katharina Lorenz , Sergio Pereira , Ian Watson , Thomas Sadler , Haoning Li , Vitaly Zubialevich , Peter Parbrook Physica Status Solidi (c) DOI: 10.1002/pssc.201200596 Show Abstract ▼ Abstract: X-ray Reciprocal Space Mapping (RSM) is a powerful tool to explore the structure of semiconductor materials. However, conventional lab-based RSMs are usually measured in two dimensions (2D) ignoring the third dimension of diffraction-space volume. We report the use of a combination of X-ray microfocusing and state-of-the-art 2D area detectors to study the full volume of diffraction–space while probing III-nitride materials on the microscale.	Dec 2012
B18-Core EXAFS I06-Nanoscience	Induced magnetic moment of Eu3+ ions in GaN S. Kachkanov , M. J. Wallace , G. Van Der Laan , S. S. Dhesi , S. A. Cavill , Y. Fujiwara , K. P. O'Donnell Scientific Reports 2 (969) DOI: 10.1038/srep00969 PMID: 23236589 Open Access Show Abstract ▼ Abstract: Magnetic semiconductors with coupled magnetic and electronic properties are of high technological and fundamental importance. Rare-earth elements can be used to introduce magnetic moments associated with the uncompensated spin of 4f-electrons into the semiconductor hosts. The luminescence produced by rare-earth doped semiconductors also attracts considerable interest due to the possibility of electrical excitation of characteristic sharp emission lines from intra 4f-shell transitions. Recently, electroluminescence of Eu-doped GaN in current-injection mode was demonstrated in p-n junction diode structures grown by organometallic vapour phase epitaxy. Unlike most other trivalent rare-earth ions, Eu3+ ions possess no magnetic moment in the ground state. Here we report the detection of an induced magnetic moment of Eu3+ ions in GaN which is associated with the 7F2 final state of 5D0→7F2 optical transitions emitting at 622 nm. The prospect of controlling magnetic moments electrically or optically will lead to the development of novel magneto-optic devices.	Dec 2012
B16-Test Beamline	InGaN epilayer characterization by microfocused x-ray reciprocal space mapping V. Kachkanov , I. P. Dolbnya , K. P. O'Donnell , R. W. Martin , P. R. Edwards , S. Pereira Applied Physics Letters 99 (18) DOI: 10.1063/1.3658619 Show Abstract ▼ Abstract: We report the use of microfocused three-dimensional x-ray reciprocal space mapping to study InGaN epilayers with average InN content ∼20%-22%. Analysis of the full volume of reciprocal space, while probing samples on the microscale with a focused x-ray beam, allowed us to gain valuable information about the nanostructure of InN-rich InGaN epilayers. It is found that “seed” InGaN mosaic nanocrystallites are twisted with respect to the ensemble average and strain-free. The initial stages of InGaN-on-GaN epitaxial growth, therefore, conform to the Volmer-Weber growth mechanism with “seeds” nucleated on strain fields generated by the a-type edge dislocations.	Nov 2011
	Local structure of luminescent InGaN alloys V. Kachkanov , K. P. O'Donnell , R. W. Martin , J. F. W. Mosselmans , S. Pereira Applied Physics Letters 89 (10) DOI: 10.1063/1.2346172 Show Abstract ▼ Abstract: Comparative Ga and In K-edge extended x-ray absorption fine structure studies provide the first direct evidence of an inequality of mean In-Ga and Ga-In next-nearest neighbor separations in InGaN alloys. The degree of inequality increases with decreasing InN fraction x in the range accessible to extended x-ray absorption fine structure analysis of alloys (0.9 < x < 0.1). Its concurrence with an increase of luminescence efficiency in this composition range suggests that the breakdown of In/Ga randomness in InGaN is correlated with efficient radiative recombination in blue-green light emitting devices. (c) 2006 American Institute of Physics.	Sep 2006

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