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Optical properties and degradation of deep ultraviolet AIGaN-based light-emitting diodes
KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
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 [en]
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: urn:nbn:se:kth:diva-37917ISBN: 978-91-7501-065-6 (print)OAI: oai:DiVA.org:kth-37917DiVA: diva2:435650
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
List of papers
1. Intrinsic electric fields in AlGaN quantum wells
Open this publication in new window or tab >>Intrinsic electric fields in AlGaN quantum wells
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2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 8Article in journal (Refereed) Published
Abstract [en]

Intrinsic electric fields in AlxGa1-xN/AlyGa1-yN quantum wells embedded into p-i-n structures are studied using photoluminescence experiments. Spectral shifts induced by external bias and screening by photoexcited carriers allow evaluating the intrinsic fields caused by piezoelectric and spontaneous polarizations. In quantum wells with low Al content, the field is about 1 MV/cm, which is in agreement with theoretical estimations. For high Al molar fractions (35% well, 50% barrier), the extracted intrinsic field is lower and, most importantly, has the opposite sign to that predicted by the theory.

Keyword
light-emitting-diodes, piezoelectric field, polarization
Identifiers
urn:nbn:se:kth:diva-16404 (URN)10.1063/1.2679864 (DOI)000244420600029 ()2-s2.0-33847221017 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Screening dynamics of intrinsic electric field in AlGaN quantum wells
Open this publication in new window or tab >>Screening dynamics of intrinsic electric field in AlGaN quantum wells
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2008 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, no 6, 061907- p.Article in journal (Refereed) Published
Abstract [en]

Shift of the transition energy after pulsed optical excitation in Al0.35Ga0.65N/Al0.49Ga0.51N quantum well (QW) structures with varying well width has been studied by time-resolved photoluminescence. The shift dynamics, which is due to descreening of the intrinsic electric field, has characteristic times similar to carrier lifetimes revealing negligible influence of trapped carriers on screening. Comparison of the experimental spectral shifts with the calculations has shown that the intrinsic field in our AlGaN QWs is about 0.4-0.5 MV/cm, which is about a factor of two smaller than the value calculated using the theoretical polarization constants.

Keyword
POLARIZATION; PHOTOLUMINESCENCE; HETEROSTRUCTURES; INGAN/GAN
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-36438 (URN)10.1063/1.2857467 (DOI)000253237900029 ()2-s2.0-39349097863 (Scopus ID)
Note
QC 20110712Available from: 2011-07-12 Created: 2011-07-12 Last updated: 2017-12-11Bibliographically approved
3. Carrier lifetimes in AlGaN quantum wells: electric field and excitonic effects
Open this publication in new window or tab >>Carrier lifetimes in AlGaN quantum wells: electric field and excitonic effects
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2008 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, no 15Article in journal (Refereed) Published
Abstract [en]

Photoexcited carrier dynamics in a 280 nm AlGaN quantum well (QW) light emitting diode has been studied by time-resolved photoluminescence at forward and reverse bias. Long ( for AlGaN QWs with high Al content) room temperature carrier lifetimes of about 600 ps were measured with only a slight dependence on bias. These lifetimes are much longer than calculated free carrier tunnelling and thermionic emission times, pointing out the importance of excitonic effects for carrier dynamics in AlGaN QWs.

Keyword
binding-energy, photoluminescence, polarization, enhancement
Identifiers
urn:nbn:se:kth:diva-17713 (URN)10.1088/0022-3727/41/15/155116 (DOI)000257839700037 ()2-s2.0-49749147151 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
4. Time-resolved luminescence studies of proton-implanted GaN
Open this publication in new window or tab >>Time-resolved luminescence studies of proton-implanted GaN
2009 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 95, no 11Article in journal (Refereed) Published
Abstract [en]

Time-resolved photoluminescence measurements performed on proton implanted and annealed GaN layers have shown that carrier lifetime can be tuned over two orders of magnitude and, at implantation dose of 1 x 10(15) cm(-2), decreases down to a few picoseconds. With annealing at temperatures between 250 and 750 degrees C, carrier lifetime, contrary to electrical characteristics, is only slightly restored, indicating that electrical compensation and carrier dynamics are governed by different defects. Ga vacancies, free and bound at threading dislocations, are suggested as the most probable defects, responsible for electrical compensation and carrier lifetime quenching.

Keyword
n-type gan, defects, recombination, dislocations, acceptors, electron
Identifiers
urn:nbn:se:kth:diva-18786 (URN)10.1063/1.3226108 (DOI)000270096900041 ()2-s2.0-70349479052 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
5. Aging of AlGaN quantum well light emitting diode studied by scanning near-field optical spectroscopy
Open this publication in new window or tab >>Aging of AlGaN quantum well light emitting diode studied by scanning near-field optical spectroscopy
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2009 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 95, no 18Article in journal (Refereed) Published
Abstract [en]

Emission from a 285 nm AlGaN quantum well light emitting diode has been studied by scanning near-field optical spectroscopy. The scans revealed micrometer-size domainlike areas emitting with a higher intensity and at a longer wavelength; presumably, because of a lower AlN molar fraction in these regions. Experiments performed on different days have shown that with time, intensity from these spots increases and emission wavelength shifts to the red, indicating a further change in the quantum well alloy composition. This has allowed distinguishing an aging mechanism that involves locally increased current, heating, and atom migration.

Keyword
ageing, aluminium compounds, gallium compounds, III-V semiconductors, light emitting diodes, semiconductor quantum wells, wide band gap, semiconductors, chemical-vapor-deposition, uv leds, gan, aln, nm
Identifiers
urn:nbn:se:kth:diva-18947 (URN)10.1063/1.3262964 (DOI)000271666800033 ()2-s2.0-71049166859 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
6. Dynamics of carrier recombination and localization in AlGaN quantum wells studied by time-resolved transmission spectroscopy
Open this publication in new window or tab >>Dynamics of carrier recombination and localization in AlGaN quantum wells studied by time-resolved transmission spectroscopy
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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.

Keyword
relaxation
Identifiers
urn:nbn:se:kth:diva-18738 (URN)10.1063/1.3222972 (DOI)000269625800022 ()2-s2.0-69949157239 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
7. High current-induced degradation of AlGaN ultraviolet light emitting diodes
Open this publication in new window or tab >>High current-induced degradation of AlGaN ultraviolet light emitting diodes
2011 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, no 10, 103108- p.Article in journal (Refereed) Published
Abstract [en]

Degradation under high current stress of AlGaN quantum well based light emitting diodes emitting at 285 and 310 nm has been studied using electroluminescence, time-resolved photoluminescence and current-voltage experimental techniques. The measurements have revealed that during aging decrease of the emission intensity is accompanied by increase of the tunneling current, increase of the nitrogen vacancy concentration and partial compensation of the p-doping. The main role in the device degradation has been ascribed to formation of tunneling conductivity channels, probably, via activation of the closed core screw dislocations with the help of nitrogen vacancies. Carrier lifetimes in the quantum wells and the p-cladding were found to be unaffected by the aging process, suggesting that the nonradiative recombination has a lesser influence on the device degradation.

Keyword
GAN, NM, DISLOCATIONS, RELIABILITY, MECHANISMS, EMISSION, GROWTH, LEDS
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-36236 (URN)10.1063/1.3590149 (DOI)000292115900033 ()2-s2.0-79958820030 (Scopus ID)
Note
QC 20110711Available from: 2011-07-11 Created: 2011-07-11 Last updated: 2017-12-11Bibliographically approved
8. Localization potentials in AlGaN epitaxial films studied by scanning near-field optical spectroscopy
Open this publication in new window or tab >>Localization potentials in AlGaN epitaxial films studied by scanning near-field optical spectroscopy
Show others...
2011 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, no 11Article in journal (Refereed) 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.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-36870 (URN)10.1063/1.3594239 (DOI)000292214700037 ()2-s2.0-79959480315 (Scopus ID)
Note
QC 20110721Available from: 2011-07-21 Created: 2011-07-18 Last updated: 2017-12-08Bibliographically approved

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