The atomic structure of polar and non-polar InGaN quantum wells and the green gap problem

C. J. Humphreys, J. T. Griffiths, F. Tang, F. Oehler, S D Findlay, C Zheng, J Etheridge, T. L. Martin, P. A J Bagot, M. P. Moody, D. Sutherland, P. Dawson, S. Schulz, S. Zhang, W. Y. Fu, T. Zhu, M. J. Kappers, R. A. Oliver

Research output: Contribution to journalArticleResearchpeer-review

Abstract

We have used high resolution transmission electron microscopy (HRTEM), aberration-corrected quantitative scanning transmission electron microscopy (Q-STEM), atom probe tomography (APT) and X-ray diffraction (XRD) to study the atomic structure of (0001) polar and (11-20) non-polar InGaN quantum wells (QWs). This paper provides an overview of the results. Polar (0001) InGaN in QWs is a random alloy, with In replacing Ga randomly. The InGaN QWs have atomic height interface steps, resulting in QW width fluctuations. The electrons are localised at the top QW interface by the built-in electric field and the well-width fluctuations, with a localisation energy of typically 20. meV. The holes are localised near the bottom QW interface, by indium fluctuations in the random alloy, with a localisation energy of typically 60. meV. On the other hand, the non-polar (11-20) InGaN QWs contain nanometre-scale indium-rich clusters which we suggest localise the carriers and produce longer wavelength (lower energy) emission than from random alloy non-polar InGaN QWs of the same average composition. The reason for the indium-rich clusters in non-polar (11-20) InGaN QWs is not yet clear, but may be connected to the lower QW growth temperature for the (11-20) InGaN QWs compared to the (0001) polar InGaN QWs.

Original languageEnglish
Pages (from-to)93–98
Number of pages6
JournalUltramicroscopy
Volume176
DOIs
Publication statusPublished - 2017

Keywords

  • Aberration-corrected electron microscopy
  • Atomic structure
  • Gallium nitride
  • Quantitative STEM
  • Quantum wells

Cite this

Humphreys, C. J., Griffiths, J. T., Tang, F., Oehler, F., Findlay, S. D., Zheng, C., ... Oliver, R. A. (2017). The atomic structure of polar and non-polar InGaN quantum wells and the green gap problem. Ultramicroscopy, 176, 93–98. https://doi.org/10.1016/j.ultramic.2017.01.019
Humphreys, C. J. ; Griffiths, J. T. ; Tang, F. ; Oehler, F. ; Findlay, S D ; Zheng, C ; Etheridge, J ; Martin, T. L. ; Bagot, P. A J ; Moody, M. P. ; Sutherland, D. ; Dawson, P. ; Schulz, S. ; Zhang, S. ; Fu, W. Y. ; Zhu, T. ; Kappers, M. J. ; Oliver, R. A. / The atomic structure of polar and non-polar InGaN quantum wells and the green gap problem. In: Ultramicroscopy. 2017 ; Vol. 176. pp. 93–98.
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title = "The atomic structure of polar and non-polar InGaN quantum wells and the green gap problem",
abstract = "We have used high resolution transmission electron microscopy (HRTEM), aberration-corrected quantitative scanning transmission electron microscopy (Q-STEM), atom probe tomography (APT) and X-ray diffraction (XRD) to study the atomic structure of (0001) polar and (11-20) non-polar InGaN quantum wells (QWs). This paper provides an overview of the results. Polar (0001) InGaN in QWs is a random alloy, with In replacing Ga randomly. The InGaN QWs have atomic height interface steps, resulting in QW width fluctuations. The electrons are localised at the top QW interface by the built-in electric field and the well-width fluctuations, with a localisation energy of typically 20. meV. The holes are localised near the bottom QW interface, by indium fluctuations in the random alloy, with a localisation energy of typically 60. meV. On the other hand, the non-polar (11-20) InGaN QWs contain nanometre-scale indium-rich clusters which we suggest localise the carriers and produce longer wavelength (lower energy) emission than from random alloy non-polar InGaN QWs of the same average composition. The reason for the indium-rich clusters in non-polar (11-20) InGaN QWs is not yet clear, but may be connected to the lower QW growth temperature for the (11-20) InGaN QWs compared to the (0001) polar InGaN QWs.",
keywords = "Aberration-corrected electron microscopy, Atomic structure, Gallium nitride, Quantitative STEM, Quantum wells",
author = "Humphreys, {C. J.} and Griffiths, {J. T.} and F. Tang and F. Oehler and Findlay, {S D} and C Zheng and J Etheridge and Martin, {T. L.} and Bagot, {P. A J} and Moody, {M. P.} and D. Sutherland and P. Dawson and S. Schulz and S. Zhang and Fu, {W. Y.} and T. Zhu and Kappers, {M. J.} and Oliver, {R. A.}",
year = "2017",
doi = "10.1016/j.ultramic.2017.01.019",
language = "English",
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Humphreys, CJ, Griffiths, JT, Tang, F, Oehler, F, Findlay, SD, Zheng, C, Etheridge, J, Martin, TL, Bagot, PAJ, Moody, MP, Sutherland, D, Dawson, P, Schulz, S, Zhang, S, Fu, WY, Zhu, T, Kappers, MJ & Oliver, RA 2017, 'The atomic structure of polar and non-polar InGaN quantum wells and the green gap problem', Ultramicroscopy, vol. 176, pp. 93–98. https://doi.org/10.1016/j.ultramic.2017.01.019

The atomic structure of polar and non-polar InGaN quantum wells and the green gap problem. / Humphreys, C. J.; Griffiths, J. T.; Tang, F.; Oehler, F.; Findlay, S D; Zheng, C; Etheridge, J; Martin, T. L.; Bagot, P. A J; Moody, M. P.; Sutherland, D.; Dawson, P.; Schulz, S.; Zhang, S.; Fu, W. Y.; Zhu, T.; Kappers, M. J.; Oliver, R. A.

In: Ultramicroscopy, Vol. 176, 2017, p. 93–98.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - The atomic structure of polar and non-polar InGaN quantum wells and the green gap problem

AU - Humphreys, C. J.

AU - Griffiths, J. T.

AU - Tang, F.

AU - Oehler, F.

AU - Findlay, S D

AU - Zheng, C

AU - Etheridge, J

AU - Martin, T. L.

AU - Bagot, P. A J

AU - Moody, M. P.

AU - Sutherland, D.

AU - Dawson, P.

AU - Schulz, S.

AU - Zhang, S.

AU - Fu, W. Y.

AU - Zhu, T.

AU - Kappers, M. J.

AU - Oliver, R. A.

PY - 2017

Y1 - 2017

N2 - We have used high resolution transmission electron microscopy (HRTEM), aberration-corrected quantitative scanning transmission electron microscopy (Q-STEM), atom probe tomography (APT) and X-ray diffraction (XRD) to study the atomic structure of (0001) polar and (11-20) non-polar InGaN quantum wells (QWs). This paper provides an overview of the results. Polar (0001) InGaN in QWs is a random alloy, with In replacing Ga randomly. The InGaN QWs have atomic height interface steps, resulting in QW width fluctuations. The electrons are localised at the top QW interface by the built-in electric field and the well-width fluctuations, with a localisation energy of typically 20. meV. The holes are localised near the bottom QW interface, by indium fluctuations in the random alloy, with a localisation energy of typically 60. meV. On the other hand, the non-polar (11-20) InGaN QWs contain nanometre-scale indium-rich clusters which we suggest localise the carriers and produce longer wavelength (lower energy) emission than from random alloy non-polar InGaN QWs of the same average composition. The reason for the indium-rich clusters in non-polar (11-20) InGaN QWs is not yet clear, but may be connected to the lower QW growth temperature for the (11-20) InGaN QWs compared to the (0001) polar InGaN QWs.

AB - We have used high resolution transmission electron microscopy (HRTEM), aberration-corrected quantitative scanning transmission electron microscopy (Q-STEM), atom probe tomography (APT) and X-ray diffraction (XRD) to study the atomic structure of (0001) polar and (11-20) non-polar InGaN quantum wells (QWs). This paper provides an overview of the results. Polar (0001) InGaN in QWs is a random alloy, with In replacing Ga randomly. The InGaN QWs have atomic height interface steps, resulting in QW width fluctuations. The electrons are localised at the top QW interface by the built-in electric field and the well-width fluctuations, with a localisation energy of typically 20. meV. The holes are localised near the bottom QW interface, by indium fluctuations in the random alloy, with a localisation energy of typically 60. meV. On the other hand, the non-polar (11-20) InGaN QWs contain nanometre-scale indium-rich clusters which we suggest localise the carriers and produce longer wavelength (lower energy) emission than from random alloy non-polar InGaN QWs of the same average composition. The reason for the indium-rich clusters in non-polar (11-20) InGaN QWs is not yet clear, but may be connected to the lower QW growth temperature for the (11-20) InGaN QWs compared to the (0001) polar InGaN QWs.

KW - Aberration-corrected electron microscopy

KW - Atomic structure

KW - Gallium nitride

KW - Quantitative STEM

KW - Quantum wells

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U2 - 10.1016/j.ultramic.2017.01.019

DO - 10.1016/j.ultramic.2017.01.019

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