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Dynamics of polarized photoluminescence in m-plane InGaN/GaN quantum wells
KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.ORCID iD: 0000-0002-4606-4865
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2010 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 2, 023101- p.Article in journal (Refereed) Published
Abstract [en]

Spectrally-, polarization-, and time-resolved photoluminescence (PL) experiments have been performed on 2.5 nm thick m-plane single InGaN quantum wells. It has been found that PL decay is mainly determined by nonradiative recombination through several types of recombination centers, while PL rise is largely affected by exciton transfer into localization minima. Prolonged PL rise times and time-dependent spectral shift were used to study exciton transfer into the localization centers. CharacteristiC time of the exciton transfer is 80-100 ps at lower temperatures and about 50 ps at room temperature, which corresponds to the exciton diffusion length of 200-500 nm. Degree of PL linear polarization was found to decrease at a similar rate. Decreased PL polarization for the localized excitons suggests that the localization centers are related to areas with relaxed strain. (C) 2010 American Institute of Physics. [doi:10.1063/1.3460278]

Place, publisher, year, edition, pages
2010. Vol. 108, no 2, 023101- p.
National Category
Atom and Molecular Physics and Optics
URN: urn:nbn:se:kth:diva-26889DOI: 10.1063/1.3460278ISI: 000280909900001ScopusID: 2-s2.0-77955822740OAI: diva2:373162

QC 20101130

Available from: 2010-11-30 Created: 2010-11-29 Last updated: 2012-11-01Bibliographically approved
In thesis
1. Localization effects in ternary nitride semiconductors
Open this publication in new window or tab >>Localization effects in ternary nitride semiconductors
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

InGaN based blue and near-ultraviolet light emitting diodes and laser diodes have been successfully commercialized for many applications such as general lighting, display backlighting and high density optical storage devices. Despite having a comparably high defect density, these devices are known for their efficient operation, which is attributed to localization in potential fluctuations preventing carriers from reaching the centers of nonradiative recombination. Nitride research is currently headed towards improving deep ultraviolet AlGaN and green InGaN emitters with higher Al and In molar fractions. The efficiency of these devices trails behind the blue counterparts as the carrier localization does not seem to aid in supressing nonradiative losses. In addition, the operation of ternary nitride heterostructure based devices is further complicated by the presence of large built-in electric fields. Although the problem can be ameliorated by growing structures in nonpolar or semipolar directions, the step from research to production still awaits.

In this thesis, carrier dynamics and localization effects have been studied in three different nitride ternary compounds: AlGaN epitaxial layers and quantum wells with high Al content, nonpolar m-plane InGaN/GaN quantum wells and lattice matched AlInN/GaN heterostructures. The experimental methods of this work mainly consist of spectroscopy techniques such as time-resolved photoluminescence and differential transmission pump-probe measurements as well as spatial photoluminescence mapping by means of scanning near-field microscopy.

The comparison of luminescence and differential transmission measurements has allowed estimating the localization depth in AlGaN quantum wells. Additionally, it has been demonstrated that the polarization degree of luminescence from m-InGaN quantum wells decreases as carriers diffuse to localization centers.What is more, dual-scale localization potential has been evidenced by near-field measurements in both AlGaN and m-InGaN. Larger scale potential fluctuation have been observed directly and the depth of nanoscopic localization has been estimated theoretically from the recorded linewidth of the near-field spectra. Lastly, efficient carrier transport has been observed through AlInN layer despite large alloy inhomogeneities evidenced by broad luminescence spectra and the huge Stokes shift. Inhomogeneous luminescence from the underlying GaN layer has been linked to the fluctuations of the built-in electric field at the AlInN/GaN interface.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xii, 70 p.
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2012:18
AlGaN, InGaN, AlInN, LEDs, near-field microscopy, carrier dynamics, alloy fluctuations, carrier localization, built-in electric field, nonpolar planes, polarized luminescence
National Category
Condensed Matter Physics Atom and Molecular Physics and Optics
urn:nbn:se:kth:diva-104290 (URN)978-91-7501-530-9 (ISBN)
Public defence
2012-11-19, sal C2, KTH-Electrum, Isafjordsgatan 26, Kista, 10:30 (English)
Swedish Research Council

QC 20121101

Available from: 2012-11-01 Created: 2012-10-31 Last updated: 2012-11-01Bibliographically approved

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