Skip to main content Accessibility help

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

  • Thomas Walther (a1), Xiaoyi Wang (a1), Veerendra C. Angadi (a1), Pierre Ruterana (a2), Paolo Longo (a3) and Toshihiro Aoki (a4)...
  • Please note a correction has been issued for this article.


Phase separation of In x Ga1−x N into Ga-rich and In-rich regions has been studied by electron energy-loss spectroscopy (EELS) in a monochromated, aberration corrected scanning transmission electron microscope (STEM). We analyze the full spectral information contained in EELS of InGaN, combining for the first time studies of high-energy and low-energy ionization edges, plasmon, and valence losses. Elemental maps of the N K, In M4,5 and Ga L2,3 edges recorded by spectrum imaging at 100 kV reveal sub-nm fluctuations of the local indium content. The low energetic edges of Ga M4,5 and In N4,5 partially overlap with the plasmon peaks. Both have been fitted iteratively to a linear superimposition of reference spectra for GaN, InN, and InGaN, providing a direct measurement of phase separation at the nm-scale. Bandgap measurements are limited in real space by scattering delocalization rather than the electron beam size to ∼10 nm for small bandgaps, and their energetic accuracy by the method of fitting the onset of the joint density of states rather than energy resolution. For an In0.62Ga0.38N thin film we show that phase separation occurs on several length scales.


Corresponding author

a) Address all correspondence to this author. e-mail:


Hide All

Contributing Editor: Eric A. Stach


This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to

A previous error in this article has been corrected, see 10.1557/jmr.2017.245.



Hide All
1. Ruterana, P., Nouet, G., Van der Stricht, W., Moerman, I., and Considine, L.: Chemical ordering in wurtzite In x Ga1−x N layers grown on (0001) sapphire by metalorganic vapor phase epitaxy. Appl. Phys. Lett. 72(14), 1742 (1998).
2. Zhu, D.M., You, S., Detchprohm, T., Paskova, T., Preble, E.A., Hanser, D., and Wetzel, C.: Inclined dislocation-pair relaxation mechanism in homoepitaxial green GaInN/GaN light-emitting diodes. Phys. Rev. B: Condens. Matter Mater. Phys. 81(12), 125325 (2010).
3. Doppalapudi, D., Basu, S.N., Ludwig, K.F. Jr., and Moustakas, T.D.: Phase separation and ordering in InGaN alloys grown by molecular beam epitaxy. J. Appl. Phys. 84(3), 1389 (1998).
4. Park, I-K., Kwon, M.K., Baek, S-H., Ok, Y-W., Seong, T-Y., Park, S-J., Kim, Y-S., Moon, Y-T., and Kim, D-J.: Enhancement of phase separation in the InGaN layer for self-assembled In-rich quantum dots. Appl. Phys. Lett. 87, 061906 (2005).
5. Lin, Y-S., Ma, K-J., Hsu, C., Feng, S-W., Cheng, Y-C., Liao, C-C., Yang, C-C., Chou, C-C., Lee, C-M., and Chyi, J.I.: Dependence of composition fluctuation on indium content in InGaN/GaN multiple quantum wells. Appl. Phys. Lett. 77(19), 2988 (2000).
6. Singh, R., Doppalapudi, D., Moustakas, T.D., and Romano, L.T.: Phase separation in InGaN thick films and formation of InGaN/GaN double heterostructures in the entire alloy composition. Appl. Phys. Lett. 70, 1089 (1997).
7. Ho, I.H. and Stringfellow, G.B.: Solid phase immiscibility in GaInN. Appl. Phys. Lett. 69(18), 2701 (1996).
8. Matsuoka, T., Sasaki, T., and Katsui, A.: Growth and properties of a wide-gap semiconductor indium gallium nitride. Optoelectron. Devices Technol. 5(1), 53 (1990).
9. Matsuoka, T., Yoshimoto, N., Sasaki, T., and Katsui, A.: Wide-gap semiconductor InGaN and InGaAlN grown by MOVPE. J. Electron. Mater. 21(2), 157 (1992).
10. Nakamura, S.: Growth of In x Ga1−x N compound semiconductors and high-power InGaN/AlGaN double-heterostructure violet-light-emitting diodes. Microelectron. J. 25(8), 651 (1994).
11. Shimizu, M., Hiramatsu, K., and Sawaki, N.: Metalorganic vapor-phase epitaxy growth of (In x Ga1−x N/GaN) layered structures and reduction of indium droplets. J. Cryst. Growth. 145, 209 (1994).
12. Nakamura, S., Mukai, T., Senoh, M., Nagahama, S., and Iwasa, N.: In x Ga1−x N/In y Ga1−y N superlattices grown on GaN films. J. Appl. Phys. 74(6), 3911 (1993).
13. O’Neill, J.P., Ross, I.M., Cullis, A.G., Wang, T., and Parbrook, P.J.: Electron-beam-induced segregation in InGaN/GaN multiple-quantum wells. Appl. Phys. Lett. 83(10), 1965 (2003).
14. Smeeton, T.M., Kappers, M.J., Barnard, J.S., Vickers, M.E., and Humphreys, C.J.: Electron-beam-induced strain within InGaN quantum wells: False indium “cluster” detection in the transmission electron microscope. Appl. Phys. Lett. 83(26), 5419 (2003).
15. Humphreys, C.J.: Does In form In-rich clusters in InGaN quantum wells? Philos. Mag. 87(13), 1971 (2007).
16. Baloch, K.H., Johnston-Peck, A.C., Kisslinger, K., Stach, E.A., and Gradecak, S.: Revisiting the “In-clustering” question in InGaN through the use of aberration corrected electron microscopy below the knock-on threshold. Appl. Phys. Lett. 102, 191910 (2013).
17. Wang, X., Chauvat, M-P., Ruterana, P., and Walther, T.: Investigation of phase separation in InGaN alloys by plasmon loss spectroscopy in a TEM. MRS Adv. 1(40), 27492756 (2016). doi: 10.1557/adv2016.542.
18. Wang, X., Chauvat, M.P., Ruterana, P., and Walther, T.: Combination of electron energy-loss spectroscopy and energy-dispersive x-ray spectroscopy to determine indium concentration in InGaN thin film structures. Semicond. Sci. Technol. 30(11), 114011 (2015).
19. Walther, T., Wolf, F., Recnik, A., and Mader, W.: Quantitative microstructural and spectroscopic investigation of inversion domain boundaries in zinc oxide ceramics sintered with iron oxide. Int. J. Mater. Res. 97, 934 (2006).
20. Krivanek, O.L., Ursin, J.P., Bacon, N.J., Corbin, G.J., Dellby, N., Hrncirik, P., Murfitt, M.F., Own, C.S., and Szylagyi, Z.S.: High-energy-resolution monochromator for aberration-corrected scanning transmission electron microscope/electron energy-loss spectroscopy. Phil. Trans. R. Soc., A 367(1903), 3683 (2009).
21. Bartel, T.P., Specht, P., Ho, J.C., and Kisielowski, C.: Phase separation in In x Ga1−x N. Philos. Mag. 87(13), 1983 (2007).
22. Orsal, G., El Gmili, Y., Fressengeas, N., Streque, J., Djerboub, R., Moudakir, T., Sundaram, D., Ougazzaden, A., and Salvestrini, J.P.: Bandgap energy bowing parameter of strained and relaxed InGaN layers. Opt. Mater. Express 4(5), 1030 (2014).
23. Walther, T.: An improved approach to quantitative x-ray microanalysis in (S)TEM: Thickness dependent k-factors. Proc EMAG 2009, Sheffield. J. Phys. Conf. Ser. 241, 012016 (2010).
24. Walther, T. and Wang, X.: Self-consistent method for quantifying indium content from x-ray spectra of thick compound semiconductor specimens in a transmission electron microscope. J. Microsc. 252(2), 151 (2016).
25. Amari, H., Ross, I.M., Wang, T., and Walther, T.: Characterization of InGaN/GaN epitaxial layers by aberration corrected TEM/STEM. Phys. Stat. Sol. C 9(3–4), 546 (2012).
26. Egerton, R.F.: Electron Energy-loss Spectroscopy in the Electron Microscope, 2nd ed. (Plenum Press, New York, 1996).
27. Angadi, V.C., Abhayaratne, C., and Walther, T.: Automated background subtraction technique for electron energy-loss spectroscopy and application to semiconductor heterostructures. J. Microsc. 262(2), 157 (2016).
28. Thomas, P.J. and Twesten, R.D.: A simple, model based approach for robust quantification of EELS spectra and spectrum-images. Microsc. Microanal. 18(Suppl. 2), 968 (2012).
29. Scott, J., Thomas, P.J., MacKenzie, M., McFadzean, S., Wilbrink, J., Craven, A.J., and Nicholson, W.A.P.: Near-simultaneous dual energy range EELS spectrum imaging. Ultramicrosocpy 108(12), 1586 (2008).
30. Jinschek, J.R., Erni, R., Gardner, N.F., Kim, A.Y., and Kisielowski, C.: Local indium segregation and band gap variations in high efficiency green light emitting InGaN/GaN diodes. Solid State Comm. 137, 230 (2006).
31. Albrecht, M., Grillo, V., Borysiuk, J., Remmele, T., Strunk, H.P., Walther, T., Mader, W., Prystawko, P., Leszczynski, M., Grzegory, I., and Porowski, S.: Correlating compositional, structural and optical properties of InGaN quantum wells by transmission electron microscopy. Proc. Microsc. Semicond. Mater. Conf. 2001, Oxford. Inst. Phys. Conf. Ser. 169, 267 (2001).
32. Erni, R. and Browning, N.D.: Valence electron energy-loss spectroscopy in monochromated scanning transmission electron microscopy. Ultramicroscopy 104(3–4), 176 (2005).
33. Walther, T. and Stegmann, H.: Preliminary results from the first monochromated and aberration corrected 200-kV field-emission scanning transmission electron microscope. Microsc. & Microanal. 12(6), 498 (2006).
34. Brockt, G. and Lakner, H.: Nanoscale EELS analysis of dielectric function and bandgap properties in GaN and related materials. Micron 31, 435 (2000).
35. Schamm, S. and Zanchi, G.: Study of the dielectric properties near the band gap by VEELS: Gap measurement in bulk materials. Ultramicroscopy 96, 559 (2003).
36. Manual, J.M., Koch, C.T., Özdöl, V.B., Sigle, W., van Aken, P.A., Garcia, R., and Morales, F.M.: Inline electron holography and VEELS for the measurement of strain in ternary and quaternary (In,Al,Ga)N alloyed thin films and its effect on bandgap energy. J. Microsc. 261(1), 27 (2016).
37. Stöger-Pollach, M. and Schattschneider, P.: The influence of relativistic energy losses on bandgap determination using valence EELS. Ultramicroscopy 107(12), 1178 (2007).
38. Müllejans, H. and French, R.H.: Insights into the electronic structure of ceramics through quantitative analysis of valence energy-loss spectroscopy. Microsc. Microanal. 6(4), 297 (2000).
39. Specht, P., Ho, J.C., Xu, X., Armitage, R., Weber, E.R., Erni, R., and Kisielowski, C.: Band transitions in wurtzite GaN and InN determined by valence electron energy loss spectroscopy. Sol. State Comm. 135, 340 (2005).
40. Erni, R. and Browning, N.D.: Quantification of the size-dependent energy gap of individual CdSe quantum dots by valence electron energy-loss spectroscopy. Ultramicroscopy 107(2–3), 267 (2007).
41. Pelá, R.R., Caetano, C., Marques, M., Ferreira, L.G., Furthmüller, J., and Teles, L.K.: Accurate band gaps of AlGaN, InGaN and AlInN alloys calculations based on LDA-1/2 approach. J. Appl. Phys. 98(15), 151907 (2011).
42. Walther, T., Cullis, A.G., Norris, D.J., and Hopkinson, M.: Nature of the Stranski-Krastanow transition during epitaxy of InGaAs on GaAs. Phys. Rev. Lett. 86(11), 2381 (2001).
43. Walther, T., Cullis, A.G., Norris, D.J., and Hopkinson, M.: How InGaAs islands form on GaAs substrates: The missing link in the explanation of the Stranski-Krastanow transition. Proc. Microsc. Semicond. Mater. Conf. 2001, Oxford. Inst. Phys. Conf. Ser. 169, 85 (2001).
44. Cullis, A.G., Norris, D.J., Walther, T., Migliorato, M.A., and Hopkinson, M.: Stranski-Krastanow transition and epitaxial island growth. Phys. Rev. B: Condens. Matter Mater. Phys. 66, 081305R (2002).



Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed

A correction has been issued for this article: