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Impact of carrier localization on recombination in InGaN quantum wells with nonbasal crystallographic orientations
KTH, School of Engineering Sciences (SCI), Applied Physics, Optics and Photonics, OFO.ORCID iD: 0000-0002-5007-6893
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 [en]
InGaN, quantum well, semipolar, nonpolar, near-field microscopy, carrier localization, carrier transport, optical polarization
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-214599ISBN: 978-91-7729-505-1 (print)OAI: oai:DiVA.org:kth-214599DiVA, id: diva2:1142091
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
List of papers
1. Scanning near-field microscopy of carrier lifetimes in m-plane InGaN quantum wells
Open this publication in new window or tab >>Scanning near-field microscopy of carrier lifetimes in m-plane InGaN quantum wells
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2017 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 110, no 3, article id 031109Article in journal (Refereed) Published
Abstract [en]

Time-resolved scanning near-field photoluminescence (PL) spectroscopy was applied to map carrier lifetimes in wide m-plane InGaN/GaN quantum wells grown on on-axis and miscut substrates. Both radiative and nonradiative lifetimes were found to be spatially nonuniform. Lifetime variations were smaller for quantum wells grown on miscut, as compared to on-axis substrates. Correlation with surface topography showed that largest deviations of recombination times occur at +c planes of pyramidal hillocks of the on-axis sample. Observed correlation between radiative lifetimes and PL peak wavelength was assigned to a partial electron localization.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
Keywords
Photoluminescence spectroscopy, Surface topography, Electron localizations, InGaN quantum wells, InGaN/GaN quantum well, Largest deviation, Non-radiative lifetimes, Radiative lifetime, Scanning near field microscopy, Time-resolved scanning, Semiconductor quantum wells
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-202216 (URN)10.1063/1.4974297 (DOI)000392836900009 ()2-s2.0-85009999442 (Scopus ID)
Note

Funding text: The research at KTH was performed within the frame of Linnaeus Excellence Center for Advanced Optics and Photonics (ADOPT) and was financially supported by the Swedish Energy Agency (Contract No. 36652-1) and the Swedish Research Council (Contract No. 621-2013-4096). The work at UCSB was supported by the Solid State Lighting and Energy Electronics Center (SSLEEC). QC 20170320

Available from: 2017-03-20 Created: 2017-03-20 Last updated: 2018-05-21Bibliographically approved
2. Influence of well width fluctuations on recombination properties in semipolar InGaN quantum wells studied by time- and spatially-resolved near-field photoluminescence
Open this publication in new window or tab >>Influence of well width fluctuations on recombination properties in semipolar InGaN quantum wells studied by time- and spatially-resolved near-field photoluminescence
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2017 (English)In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 7, no 9, article id 3116Article in journal (Refereed) Published
Abstract [en]

Scanning near-field photoluminescence spectroscopy has been applied to distinguish the relevance of quantum well (QW) alloy composition and well width fluctuations on emission linewidth and recombination times in semipolar (2021) plane InGaN QWs. It has been found that well width fluctuations, compared to variations of InGaN alloy composition, play a negligible role in defining the photoluminescence linewidth. However, the well width strongly affects the recombination times. Prolonged radiative and nonradiative carrier lifetimes in wide QWs have been attributed to electron and hole separation by in-plane electric fields caused by nonplanarity of QW interfaces.

Place, publisher, year, edition, pages
Optical Society of America, 2017
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-214578 (URN)10.1364/OME.7.003116 (DOI)000408952600006 ()2-s2.0-85027119930 (Scopus ID)
Funder
Swedish Research Council, 621-2013-4096
Note

QC 20170918

Available from: 2017-09-17 Created: 2017-09-17 Last updated: 2018-05-21Bibliographically approved
3. High spatial uniformity of photoluminescence spectra in semipolar (20(2)over-bar1) plane InGaN/GaN quantum wells
Open this publication in new window or tab >>High spatial uniformity of photoluminescence spectra in semipolar (20(2)over-bar1) plane InGaN/GaN quantum wells
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2015 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 2, p. 023111-Article in journal (Refereed) Published
Abstract [en]

Scanning near-field optical spectroscopy was applied to study spatial variations of emission spectra at room temperature in semipolar (20 (2) over bar1) InxGa(1-x)N/GaN single quantum wells (QWs) for 0:11 <= x <= 0:36. Photoluminescence (PL) was found to be highly uniform, with peak wavelength deviations and peak intensity deviations divided by average values in the range of 6-12 meV and 0.03-0.07, respectively. Near-field maps of PL parameters showed large, similar to 5 to 10 mu m size areas of similar values, as opposed to 100 nm scale variations, often reported for InGaN QWs. The near-field PL spectra were found to broaden with increasing InN molar fraction. In the low In content QWs, the broadening is primarily determined by the random cation distribution, while for larger InN molar fractions 10 nm scale localization sites with increasingly deeper band potentials are suggested as the linewidth broadening cause.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-160387 (URN)10.1063/1.4905854 (DOI)000348129300011 ()2-s2.0-84923666851 (Scopus ID)
Funder
Swedish Energy Agency, 36652-1Swedish Research Council, 621-2013-4096
Note

QC 20150226

Available from: 2015-02-26 Created: 2015-02-19 Last updated: 2017-12-04Bibliographically approved
4. Impact of carrier localization on radiative recombination times in semipolar (2021) plane InGaN/GaN quantum wells
Open this publication in new window or tab >>Impact of carrier localization on radiative recombination times in semipolar (2021) plane InGaN/GaN quantum wells
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2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 21, article id 211109Article in journal (Refereed) Published
Abstract [en]

Semipolar (20 (2) over bar1) plane In,Ga1-xN quantum wells (QWs) of varying alloy composition were studied by time-resolved photoluminescence. A large difference in effective radiative lifetimes. from sub-ns for x = 0.11 to similar to 30 ns for x approximate to 0.35 was found. This effect is attributed to different properties of carrier localization. In low In content QWs. recombination at extended states with short recombination times is prevalent. In QWs with a high In content, the lifetimes are increased by localization of electrons and holes at separate sites. The zigzag shape of the QW interfaces and the resulting in-plane electric field are proposed as the cause for the separate electron and hole localization.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2015
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-180129 (URN)10.1063/1.4936386 (DOI)000365677500009 ()2-s2.0-84948451946 (Scopus ID)
Note

QC 20160114

Available from: 2016-01-14 Created: 2016-01-07 Last updated: 2017-11-30Bibliographically approved
5. Polarization-Resolved Near-Field Spectroscopy of Localized States in m -Plane InxGa1-x N/Ga N Quantum Wells
Open this publication in new window or tab >>Polarization-Resolved Near-Field Spectroscopy of Localized States in m -Plane InxGa1-x N/Ga N Quantum Wells
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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
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-214571 (URN)10.1103/PhysRevApplied.7.064033 (DOI)000404555000002 ()2-s2.0-85021732534 (Scopus ID)
Note

QC 20170918

Available from: 2017-09-17 Created: 2017-09-17 Last updated: 2017-09-18Bibliographically approved
6. Highly polarized photoluminescence and its dynamics in semipolar (20(2)over-bar(1)over-bar) InGaN/GaN quantum well
Open this publication in new window or tab >>Highly polarized photoluminescence and its dynamics in semipolar (20(2)over-bar(1)over-bar) InGaN/GaN quantum well
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2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 104, no 11, p. 111113-Article in journal (Refereed) Published
Abstract [en]

Very high polarization degree of 0.98, considerably larger than theoretical predictions, has been measured in (20 (2) over bar(1) over bar) In(0.24)Ga(0.7)6N/GaN quantum well by low temperature photoluminescence. With increasing temperature, the polarization degree decreases due to thermal population of the excited valence band level. This effect suggests an accurate method to determine the interlevel energy, which, for the studied well, is 32 meV. Time-resolved photoluminescence measurements set radiative recombination times between 2 and 12 ns for temperatures from 3 to 300 K. Nonradiative recombination was found to be slow, over 2 ns at 300 K, taking place via traps with activation energy of 0.19 eV.

Keywords
Increasing temperatures, InGaN/GaN quantum well, Low temperature photoluminescence, Non-radiative recombinations, Polarization degree, Polarized photoluminescence, Radiative recombination, Time-resolved photoluminescence
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-144947 (URN)10.1063/1.4869459 (DOI)000333252300013 ()2-s2.0-84897888589 (Scopus ID)
Funder
Swedish Energy Agency, 36652-1Knut and Alice Wallenberg Foundation
Note

QC 20140505

Available from: 2014-05-05 Created: 2014-05-05 Last updated: 2017-12-05Bibliographically approved
7. Direct measurement of nanoscale lateral carrier diffusion: toward scanning diffusion microscopy
Open this publication in new window or tab >>Direct measurement of nanoscale lateral carrier diffusion: toward scanning diffusion microscopy
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2017 (English)In: ACS Photonics, E-ISSN 2330-4022Article 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

Keywords
Scanning near field optical microcopy, photoluminescence, diffusion, recombination, InGaN, quantum well
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-214667 (URN)
Funder
Swedish Research Council, 621-2013-4096
Note

QC 20170919

Available from: 2017-09-19 Created: 2017-09-19 Last updated: 2018-06-14Bibliographically approved

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