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Direct measurement of nanoscale lateral carrier diffusion: toward scanning diffusion microscopy
KTH, School of Engineering Sciences (SCI), Applied Physics, Optics and Photonics, OFO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Optics and Photonics, OFO. (Optics and Photonics, prof. Saulius Marcinkevicius)ORCID iD: 0000-0002-5007-6893
KTH, School of Engineering Sciences (SCI), Applied Physics, Optics and Photonics, OFO.
Materials Department, University of California, Santa Barbara.
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2017 (English)In: ACS Photonics, ISSN 2186-2311, E-ISSN 2161-5063Article in journal (Other academic) Submitted
Abstract [en]

A multimode scanning near-field optical microscopy technique allowing to map surface morphology, photoluminescence (PL) spectra in illumination and illumination-collection modes, as well as PL dynamics, all in one scan, has been developed along with a method to use it for evaluation of carrier diffusion. The method allows to measure diffusion lengths as small as ~100 nm, their anisotropy and spatial distribution, parameters remaining inaccessible to conventional far-field techniques. The procedure has been applied to study ambipolar carrier diffusion in a nonpolar m-plane InGaN/GaN quantum well. The diffusion was found to be highly anisotropic with diffusion coefficients along and perpendicular to the wurtzite c axis equal to 0.4 and 1.9 cm2/s, respectively. The large diffusion anisotropy confirms band structure calculations that suggest that the top-most valence band in m-plane InGaN quantum well is highly anisotropic

Place, publisher, year, edition, pages
2017.
Keyword [en]
Scanning near field optical microcopy, photoluminescence, diffusion, recombination, InGaN, quantum well
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-214667OAI: oai:DiVA.org:kth-214667DiVA: diva2:1142393
Funder
Swedish Research Council, 621-2013-4096
Note

QC 20170919

Available from: 2017-09-19 Created: 2017-09-19 Last updated: 2017-11-30Bibliographically 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. 67 p.
Series
TRITA-FYS, ISSN 0280-316X ; 2017:53
Keyword
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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