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Dynamics of carrier recombination and localization in AlGaN quantum wells studied by time-resolved transmission spectroscopy
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
KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
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2009 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 95, no 9Article in journal (Refereed) Published
Abstract [en]

Time-resolved transmission and photoluminescence measurements were performed on Al0.35Ga0.65N/Al0.49Ga0.51N quantum well structures with different well widths. Comparison of transmission and luminescence data shows that dynamics of electrons and holes excited into extended quantum well states are governed by nonradiative recombination. For excitation into potential minima formed by band gap fluctuations, localization of electrons was observed. Excitation energy dependence of the pump-probe transient shape allows estimating localization potential, which is about 80 meV independently of the well width, and is probably caused by fluctuations of AlN molar fraction.

Place, publisher, year, edition, pages
2009. Vol. 95, no 9
Keyword [en]
relaxation
Identifiers
URN: urn:nbn:se:kth:diva-18738DOI: 10.1063/1.3222972ISI: 000269625800022Scopus ID: 2-s2.0-69949157239OAI: oai:DiVA.org:kth-18738DiVA: diva2:336785
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Optical properties and degradation of deep ultraviolet AIGaN-based light-emitting diodes
Open this publication in new window or tab >>Optical properties and degradation of deep ultraviolet AIGaN-based light-emitting diodes
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. 98 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2011:12
Keyword
AIGaN, deep-UV LEDs, polarization fields, screening, exciton binding energy, alloy fluctuations, near-field microscopy, carrier dynamics, LED aging
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-37917 (URN)978-91-7501-065-6 (ISBN)
Public defence
2011-09-20, Sal / Hall C1, Electrum,, Isafjordsgatan 26, Kista, 13:00 (English)
Opponent
Supervisors
Note
QC 20110831Available from: 2011-08-31 Created: 2011-08-19 Last updated: 2012-02-23Bibliographically approved
2. 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.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2012:18
Keyword
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
Identifiers
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)
Opponent
Supervisors
Funder
Swedish Research Council
Note

QC 20121101

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

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