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Impact of surface morphology on the properties of light emission in InGaN epilayers
KTH, School of Engineering Sciences (SCI), Applied Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics.
Ecole Polytech Fed Lausanne, Inst Phys, CH-1015 Lausanne, Switzerland.;OSRAM Opto Semicond GmbH, D-93055 Regensburg, Germany..
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2018 (English)In: APPLIED PHYSICS EXPRESS, ISSN 1882-0778, Vol. 11, no 5, article id 051004Article in journal (Refereed) Published
Abstract [en]

Scanning near-field optical microscopy was used to study the influence of the surface morphology on the properties of light emission and alloy composition in InGaN epitaxial layers grown on GaN substrates. A strong correlation between the maps of the photoluminescence (PL) peak energy and the gradient of the surface morphology was observed. This correlation demonstrates that the In incorporation strongly depends on the geometry of the monolayer step edges that form during growth in the step-flow mode. The spatial distribution of nonradiative recombination centers-evaluated from PL intensity maps-was found to strongly anticorrelate with the local content of In atoms in the InGaN alloy. 

Place, publisher, year, edition, pages
IOP PUBLISHING LTD , 2018. Vol. 11, no 5, article id 051004
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-227748DOI: 10.7567/APEX.11.051004ISI: 000430947200001Scopus ID: 2-s2.0-85046532520OAI: oai:DiVA.org:kth-227748DiVA, id: diva2:1205729
Funder
Swedish Research CouncilSwedish Energy Agency, 45390-1
Note

QC 20180515

Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2018-10-16Bibliographically approved
In thesis
1. 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
Keywords
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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UŽdavinys, Tomas Kristijonas

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