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Localization potentials in AlGaN epitaxial films studied by scanning near-field optical spectroscopy
KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Optik.
KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Optik.
KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Optik.ORCID-id: 0000-0002-4606-4865
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2011 (Engelska)Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, nr 11Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Scanning near-field photoluminescence spectroscopy has been applied to evaluate bandgap fluctuations in epitaxial AlGaN films with the AlN molar fraction varying from 0.30 to 0.50. A dual localization pattern has been observed. The potential of the small-scale (<100 nm) localization, evaluated from the width of the photoluminescence spectra, is between 0 and 51 meV and increases with increased Al content. These potential variations have been assigned to small-scale compositional fluctuations occurring due to stress variations, dislocations, and formation of Al-rich grains during growth. Larger area potential variations of 25-40 meV, most clearly observed in the lower Al-content samples, have been attributed to Ga-rich regions close to grain boundaries or atomic layer steps. The density, size, and bandgap energy of these domains were found to be composition dependent. The lower bandgap domains were found to be strongly correlated with the regions with efficient nonradiative recombination.

Ort, förlag, år, upplaga, sidor
2011. Vol. 109, nr 11
Nationell ämneskategori
Atom- och molekylfysik och optik
Identifikatorer
URN: urn:nbn:se:kth:diva-36870DOI: 10.1063/1.3594239ISI: 000292214700037Scopus ID: 2-s2.0-79959480315OAI: oai:DiVA.org:kth-36870DiVA, id: diva2:431638
Anmärkning
QC 20110721Tillgänglig från: 2011-07-21 Skapad: 2011-07-18 Senast uppdaterad: 2017-12-08Bibliografiskt granskad
Ingår i avhandling
1. Optical properties and degradation of deep ultraviolet AIGaN-based light-emitting diodes
Öppna denna publikation i ny flik eller fönster >>Optical properties and degradation of deep ultraviolet AIGaN-based light-emitting diodes
2011 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2011. s. 98
Serie
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2011:12
Nyckelord
AIGaN, deep-UV LEDs, polarization fields, screening, exciton binding energy, alloy fluctuations, near-field microscopy, carrier dynamics, LED aging
Nationell ämneskategori
Atom- och molekylfysik och optik
Identifikatorer
urn:nbn:se:kth:diva-37917 (URN)978-91-7501-065-6 (ISBN)
Disputation
2011-09-20, Sal / Hall C1, Electrum,, Isafjordsgatan 26, Kista, 13:00 (Engelska)
Opponent
Handledare
Anmärkning
QC 20110831Tillgänglig från: 2011-08-31 Skapad: 2011-08-19 Senast uppdaterad: 2012-02-23Bibliografiskt granskad
2. Localization effects in ternary nitride semiconductors
Öppna denna publikation i ny flik eller fönster >>Localization effects in ternary nitride semiconductors
2012 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2012. s. xii, 70
Serie
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2012:18
Nyckelord
AlGaN, InGaN, AlInN, LEDs, near-field microscopy, carrier dynamics, alloy fluctuations, carrier localization, built-in electric field, nonpolar planes, polarized luminescence
Nationell ämneskategori
Den kondenserade materiens fysik Atom- och molekylfysik och optik
Identifikatorer
urn:nbn:se:kth:diva-104290 (URN)978-91-7501-530-9 (ISBN)
Disputation
2012-11-19, sal C2, KTH-Electrum, Isafjordsgatan 26, Kista, 10:30 (Engelska)
Opponent
Handledare
Forskningsfinansiär
Vetenskapsrådet
Anmärkning

QC 20121101

Tillgänglig från: 2012-11-01 Skapad: 2012-10-31 Senast uppdaterad: 2012-11-01Bibliografiskt granskad

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