Combination of electron energy-loss spectroscopy and energy dispersive x-ray spectroscopy to determine indium concentration in InGaN thin film structures

Abstract

Article:Wang, X., Chauvat, M.P., Ruterana, P. et al. (1 more author) (2015) Combination of electron energy-loss spectroscopy and energy dispersive x-ray spectroscopy to determine indium concentration in InGaN thin film structures. Semiconductor Science and Technology, 30 (11). 114011. ISSN 0268-1242 https://doi.org/10.1088/0268-1242/30/11/114011 eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. We demonstrate a method to determine the indium concentration, x, of In x Ga 1-x N thin films by combining plasmon excitation studies in electron energy-loss spectroscopy (EELS) with a novel way of quantification of the intensity of X-ray lines in energy-dispersive X-ray spectroscopy (EDXS). The plasmon peak in EELS of InGaN is relatively broad. We fitted a Lorentz function to the main plasmon peak to suppress noise and the influence from the neighbouring Ga 3d transition in the spectrum, which improves the precision in the evaluation of the plasmon peak position. As the indium concentration of InGaN is difficult to control during high temperature growth due to partial In desorption, the nominal indium concentrations provided by the growers were not considered reliable. The indium concentration obtained from EDXS quantification using Oxford Instrument ISIS 300 X-ray standard quantification software often did not agree with the nominal indium concentration, and quantification using K and L lines was inconsistent. We therefore developed a self-consistent iterative procedure to determine the In content from thickness-dependent k-factors using, as described in recent work submitted to Journal of Microscopy. When the plasmon peak position is plotted versus the indium concentration from EDXS we obtain a linear relationship over the whole compositional range, and the standard error from linear Page 1 of 10 CONFIDENTIAL -AUTHOR SUBMITTED MANUSCRIPT SST-101604. R1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 least-squares fitting shows that the indium concentration can be determined from the plasmon peak position to within...

Study of phase separation in an InGaN alloy by electron energy loss spectroscopy in an aberration corrected monochromated scanning transmission electron microscope

“…The initially flat film surfaces have been shown to roughen with increasing value of x, leading to islands with pronounced facets for x> 0.5. At the same time, dark field imaging has shown a corresponding increase in speckle contrast from the alloys [18]. This is exactly the compositional range for which phase separation has previously been identified as likely from X-ray diffraction [21].…”

“…NION UltraSTEM, 100kV, 30mrad convergence semi-angle, 90 mrad inner collection angle (HA-ADF), 45 mrad collection angle (EELS), 50ms dwell time per pixel, 128 x 128 pixel, 0.5eV/channel, 7nm field of view. [11][12][13][14][15][16][17][18][19][20] =0.16nm) along the vertical are visible. The apparent waviness of the lattice planes is due to slight thermal drift using the acquisition.…”

“…Some of these seem to preferentially nucleate above apparent holes in the underlying film, however, these holes are partially filled by carbonaceous species and it is not yet clear whether they are an artefact from preferential argon ion thinning and subsequent filling by sputtered glue. We have used integral measurements by energy-dispersive X-ray spectroscopy (EDXS) at 197kV to verify the average In content of each sample, using a recently improved quantification method based on thickness-dependent, self-consistent k-factors [23,24] which eliminates discrepancies between absorption corrections for areas of different thicknesses [25] and has given excellent linearity with the observed shift of the plasmon peak energy in EELS [18]. None of the regions investigated at higher magnifications in subsequent figures can be marked in the overview of figure 1 because, being much thinner, they are outside its field of view, as we tried to avoid irradiating these regions at 200kV prior to chemical analysis at 60-100kV, which could have implied beam electron beam damage as explained above.…”

“…We also assess the bandgap of the alloys using different fitting routines for the region of valence electron excitation, demonstrating both the possibility to measure bandgaps down to <2eV with a monochromator and the significance of scattering delocalization at such low energies, which means a spatial resolution of ~10nm is achieved despite a much smaller electron beam size. As a typical example for an alloy with x>0.5 from the above series of samples, all of which showed some degree of facetted island growth and strong speckles in weak-beam darkfield imaging [18], we have chosen an In 0.62 Ga 0.38 N thin film for this exemplary study.…”

“…a) displays a high-angle annular dark-field (HA-ADF) image of a section ~7nm wide near the bottom of the InGaN thin film, close to a <1-100> zone axis orientation. The growth direction points upwards, and clear (0002) lattice fringes (d 0002 =0.26nm) running along the horizontal and in some areas weak(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) lattice fringes (d…”