Localization of excitation in InGaN epilayers

V. Kachkanov, K. P. O'Donnell, S. Pereira, R. W. Martin

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Energy scalability of the excitation-emission spectra of InGaN epilayers, quantum wells and light-emitting diodes provided indirect evidence for a fundamental common cause of the remarkable optical properties of this commercially important semiconductor alloy. Phase segregation on the nanoscale ( accidental quantum dot formation) has generally been accepted as the mechanism of the spectral energy scaling ( K. P. O'Donnell, R. W. Martin and P. G. Middleton, Phys. Rev. Lett. 82 237 ( 1999)). Recently, however, the downsizing of the InN bandgap, from 2 to about 1 eV, has prompted a re-examination of the observations. Here, we present new structural evidence of InGaN nanostructure, obtained from a comparative analysis of Ga and In K-edge EXAFS ( extended X-ray absorption fine structure) of a wide range of InxGa1-xN epilayer samples. The mean In-Ga and Ga-In next-nearest-neighbour ( NNN) separations are found to be unequal in length for InN-poor ( 0.1 < x < 0.4) samples. The degree of inequality increases with decreasing InN fraction, x, and therefore correlates with luminescence efficiency in this range of alloy composition. We propose that the breakdown of In/Ga randomicity in InGaN alloys is associated with efficient excitation-emission in blue-green light-emitting devices. Although non-randomicity may lead to a weak quasi-localization of excitation, through the suppression of energy back-transfer, the issue of strong exciton localization in InGaN is not directly addressed by these results.

Original languageEnglish
Pages (from-to)1999-2017
Number of pages19
JournalPhilosophical Magazine
Volume87
Issue number13
Early online date17 May 2007
DOIs
Publication statusPublished - 2007

Fingerprint

excitation
energy
emission spectra
light emitting diodes
examination
breakdown
fine structure
quantum dots
excitons
retarding
quantum wells
luminescence
scaling
optical properties
causes
x rays

Keywords

  • luminescence
  • excitation
  • emissions
  • absorption

Cite this

Kachkanov, V. ; O'Donnell, K. P. ; Pereira, S. ; Martin, R. W. / Localization of excitation in InGaN epilayers. In: Philosophical Magazine. 2007 ; Vol. 87, No. 13. pp. 1999-2017.
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Localization of excitation in InGaN epilayers. / Kachkanov, V.; O'Donnell, K. P.; Pereira, S.; Martin, R. W.

In: Philosophical Magazine, Vol. 87, No. 13, 2007, p. 1999-2017.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Localization of excitation in InGaN epilayers

AU - Kachkanov, V.

AU - O'Donnell, K. P.

AU - Pereira, S.

AU - Martin, R. W.

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N2 - Energy scalability of the excitation-emission spectra of InGaN epilayers, quantum wells and light-emitting diodes provided indirect evidence for a fundamental common cause of the remarkable optical properties of this commercially important semiconductor alloy. Phase segregation on the nanoscale ( accidental quantum dot formation) has generally been accepted as the mechanism of the spectral energy scaling ( K. P. O'Donnell, R. W. Martin and P. G. Middleton, Phys. Rev. Lett. 82 237 ( 1999)). Recently, however, the downsizing of the InN bandgap, from 2 to about 1 eV, has prompted a re-examination of the observations. Here, we present new structural evidence of InGaN nanostructure, obtained from a comparative analysis of Ga and In K-edge EXAFS ( extended X-ray absorption fine structure) of a wide range of InxGa1-xN epilayer samples. The mean In-Ga and Ga-In next-nearest-neighbour ( NNN) separations are found to be unequal in length for InN-poor ( 0.1 < x < 0.4) samples. The degree of inequality increases with decreasing InN fraction, x, and therefore correlates with luminescence efficiency in this range of alloy composition. We propose that the breakdown of In/Ga randomicity in InGaN alloys is associated with efficient excitation-emission in blue-green light-emitting devices. Although non-randomicity may lead to a weak quasi-localization of excitation, through the suppression of energy back-transfer, the issue of strong exciton localization in InGaN is not directly addressed by these results.

AB - Energy scalability of the excitation-emission spectra of InGaN epilayers, quantum wells and light-emitting diodes provided indirect evidence for a fundamental common cause of the remarkable optical properties of this commercially important semiconductor alloy. Phase segregation on the nanoscale ( accidental quantum dot formation) has generally been accepted as the mechanism of the spectral energy scaling ( K. P. O'Donnell, R. W. Martin and P. G. Middleton, Phys. Rev. Lett. 82 237 ( 1999)). Recently, however, the downsizing of the InN bandgap, from 2 to about 1 eV, has prompted a re-examination of the observations. Here, we present new structural evidence of InGaN nanostructure, obtained from a comparative analysis of Ga and In K-edge EXAFS ( extended X-ray absorption fine structure) of a wide range of InxGa1-xN epilayer samples. The mean In-Ga and Ga-In next-nearest-neighbour ( NNN) separations are found to be unequal in length for InN-poor ( 0.1 < x < 0.4) samples. The degree of inequality increases with decreasing InN fraction, x, and therefore correlates with luminescence efficiency in this range of alloy composition. We propose that the breakdown of In/Ga randomicity in InGaN alloys is associated with efficient excitation-emission in blue-green light-emitting devices. Although non-randomicity may lead to a weak quasi-localization of excitation, through the suppression of energy back-transfer, the issue of strong exciton localization in InGaN is not directly addressed by these results.

KW - luminescence

KW - excitation

KW - emissions

KW - absorption

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