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Scanning near-field microscopy of carrier lifetimes in m-plane InGaN quantum wells
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.ORCID iD: 0000-0002-5007-6893
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.ORCID iD: 0000-0002-4606-4865
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
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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. Vol. 110, no 3, article id 031109
Keyword [en]
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: urn:nbn:se:kth:diva-202216DOI: 10.1063/1.4974297ISI: 000392836900009Scopus ID: 2-s2.0-85009999442OAI: oai:DiVA.org:kth-202216DiVA, id: diva2:1082997
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
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
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
2. Optical properties of GaN and InGaN studied by time- and spatially-resolved spectroscopy
Open this publication in new window or tab >>Optical properties of GaN and InGaN studied by time- and spatially-resolved spectroscopy
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The past decade has seen rapid expansion in the use of group III-nitride based devices. White InGaN LEDs are substituting incandescent light bulbs, space satellite industry adopting ion-radiation-resistant GaN transistors, and AlGaN deep UV LEDs are increasingly being used for water disinfection and air purification. Despite this success, performance and efficiency of many devices is still far from optimal with many fundamental material properties still disputed and technological issues not solved. For example, the energy difference between the lowest conduction band valleys in the case of GaN is still being debated, and an efficient white light source of monolithic three-color LED has still not been achieved, due to the poor quantum efficiency of green-emitting quantum wells.

In view of these material challenges, this thesis was dedicated to studies of GaN, InGaN and their quantum wells with the help of time- and spatially- resolved spectroscopy and numerical modeling. This work provides new insights on both the fundamental and the growth-induced properties. Specifically, the energy difference between the lowest conduction band valleys in GaN, a key parameter for electronic devices, has been experimentally evaluated. In addition, electron scattering rates and satellite valley’s effective mass have been estimated by modeling pump-probe transients with rate equations. A study on Fe doped GaN has revealed that, depending on the device operation rate, different Fe+3 states should be considered when modelling GaN:Fe-based optoelectronic devices. Moreover, electron and hole capture coefficients and their temperature dependence have been determined. It has also been demonstrated that the random alloy model could only be used to describe emission and absorption linewidths in the InGaN alloy for a very low-In-content samples. Indium incorporation into the alloy has been found to be affected by the geometry of monolayer step edges that are formed during growth. Time-resolved scanning near-field photoluminescence spectroscopy studies on non-polar and semi-polar InGaN/GaN quantum wells have demonstrated that the common assumption of a spatially uniform radiative recombination rate is not always correct. Finally, it has been found that for a moderate to high-In-content QW the photoluminescence linewidth is defined primarily by variations of alloy composition and not well width fluctuations.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. 101
Series
TRITA-SCI-FOU ; 2018:19
Keyword
Gallium nitride, InGaN, near-field microscopy, photoexcited carrier dynamics, intervalley energy, Fe centers, In incorporation
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-228230 (URN)978-91-7729-805-2 (ISBN)
Public defence
2018-06-13, Sal C Elctrum, Kistagången 16, Kista, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20180521

Available from: 2018-05-21 Created: 2018-05-20 Last updated: 2018-05-21Bibliographically approved

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