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Optical absorption edge broadening in thick InGaN layers: Random alloy atomic disorder and growth mode induced fluctuations
KTH, School of Engineering Sciences (SCI), Applied Physics.
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2018 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 3, article id 032106Article in journal (Refereed) Published
Abstract [en]

To assess the impact of random alloying on the optical properties of the InGaN alloy, high-quality InxGa1-xN (0 < x < 0.18) epilayers grown on c-plane free-standing GaN substrates are characterized both structurally and optically. The thickness (25-100 nm) was adjusted to keep these layers pseudomorphically strained over the whole range of explored indium content as checked by x-ray diffraction measurements. The evolution of the low temperature optical absorption (OA) edge line-width as a function of absorption energy, and hence the indium content, is analyzed in the framework of the random alloy model. The latter shows that the OA edge linewidth should not markedly increase above an indium content of 4%, varying from 17 meV to 30 meV for 20% indium. The experimental data initially follow the same trend with, however, a deviation from this model for indium contents exceeding only similar to 2%. Complementary room temperature near-field photoluminescence measurements carried out using a scanning near-field optical microscope combined with simultaneous surface morphology mappings reveal spatial disorder due to growth meandering. We conclude that for thick high-quality pseudomorphic InGaN layers, a deviation from pure random alloying occurs due to the interplay between indium incorporation and longer range fluctuations induced by the InGaN step-meandering growth mode.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018. Vol. 112, no 3, article id 032106
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-222433DOI: 10.1063/1.5010879ISI: 000423027300027Scopus ID: 2-s2.0-85041435015OAI: oai:DiVA.org:kth-222433DiVA, id: diva2:1185143
Note

QC 20180223

Available from: 2018-02-23 Created: 2018-02-23 Last updated: 2018-05-24Bibliographically 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)
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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 KristijonasMensi, MounirMarcinkevičius, Saulius

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