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Polarization-Resolved Near-Field Spectroscopy of Localized States in m -Plane InxGa1-x N/Ga N Quantum Wells
KTH, School of Engineering Sciences (SCI), Applied Physics, Optics and Photonics, OFO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Optics and Photonics, OFO.ORCID iD: 0000-0002-4606-4865
KTH, School of Engineering Sciences (SCI), Applied Physics, Optics and Photonics, OFO.
KTH, School of Engineering Sciences (SCI), Applied Physics. GdS Optronlab, Física Materia Condensada, Universidad de Valladolid, Valladolid, Spain.
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2017 (English)In: Physical Review Applied, Vol. 7, no 6Article in journal (Refereed) Published
Abstract [en]

We present a polarization, spectrally, and spatially resolved near-field photoluminescence (PL) measurement technique and apply it to the study of wide m-plane InxGa1-xN/GaN quantum wells grown on on-axis and miscut GaN substrates. It is found that PL originates from localized states; nevertheless, its degree of linear polarization (DLP) is high with little spatial variation. This allows an unambiguous assignment of the localized states to InxGa1-xN composition-related band potential fluctuations. Spatial PL variations, occurring due to morphology features of the on-axis samples, play a secondary role compared to the variations of the alloy composition. The large PL peak wavelength difference for polarizations parallel and perpendicular to the c axis, the weak correlation between the peak PL wavelength and the DLP, and the temperature dependence of the DLP suggest that effective potential variations and the hole mass in the second valence-band level are considerably smaller than that for the first level. DLP maps for the long wavelength PL tails have revealed well-defined regions with a small DLP, which have been attributed to a partial strain relaxation around dislocations.

Place, publisher, year, edition, pages
American Physical Society, 2017. Vol. 7, no 6
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-214571DOI: 10.1103/PhysRevApplied.7.064033ISI: 000404555000002Scopus ID: 2-s2.0-85021732534OAI: oai:DiVA.org:kth-214571DiVA, id: diva2:1141875
Note

QC 20170918

Available from: 2017-09-17 Created: 2017-09-17 Last updated: 2017-09-18Bibliographically approved
In thesis
1. Impact of carrier localization on recombination in InGaN quantum wells with nonbasal crystallographic orientations
Open this publication in new window or tab >>Impact of carrier localization on recombination in InGaN quantum wells with nonbasal crystallographic orientations
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The modern InGaN technology demonstrates high efficiencies only in the blue spectral region and low current operation modes. The growth of InGaN quantum wells (QWs) on nonbasal crystallographic planes (NBP) has potential to deliver high-power blue and green light emitting diodes and lasers. The emission properties of these QWs are largely determined by the localization of carriers in the minima of spatially inhomogeneous band potential, which affects the recombination dynamics, spectral characteristics of the emission, its optical polarization and carrier transport. Understanding it is crucial for increasing the efficiency of NBP structures to their theoretical limit.

In this thesis, the influence of carrier localization on the critical aspects of light emission has been investigated in semipolar  and nonpolar  InGaN QWs. For this purpose, novel multimode scanning near-field optical microscopy configurations have been developed, allowing mapping of the spectrally-, time-, and polarization-resolved emission.

In the nonpolar QW structures the sub-micrometer band gap fluctuations could be assigned to the selective incorporation of indium on different slopes of the undulations, while in the smoother semipolar QWs – to the nonuniformity of QW growth. The nanoscale band potential fluctuations and the carrier localization were found to increase with increasing indium percentage in the InGaN alloy. In spite to the large depth of the potential minima, the localized valence band states were found to retain properties of the corresponding bands. The reduced carrier transfer between localization sites has been suggested as a reason for the long recombination times in the green-emitting semipolar QWs. Sharp increase of the radiative lifetimes has been assigned to the effect of nanoscale electric fields resulting from nonplanar QW interfaces. Lastly, the ambipolar carrier diffusion has been measured, revealing ~100 nm diffusion length and high anisotropy.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. p. 67
Series
TRITA-FYS, ISSN 0280-316X ; 2017:53
Keywords
InGaN, quantum well, semipolar, nonpolar, near-field microscopy, carrier localization, carrier transport, optical polarization
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-214599 (URN)978-91-7729-505-1 (ISBN)
Public defence
2017-09-29, Hall C, Elektrum 229, Kista, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency, 36652-1Swedish Research Council, 621-2013- 4096
Note

QC 20170919

Available from: 2017-09-19 Created: 2017-09-18 Last updated: 2017-09-19Bibliographically approved

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