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Photoluminescence dynamics of AlGaN quantum wells with built-in electric fields and localized states
KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
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2010 (English)In: Physica Status Solidi (A) Applications and Materials, ISSN 1862-6300, Vol. 207, no 2, 423-427 p.Article in journal (Refereed) Published
Abstract [en]

We report on photoluminescence (PL) studies of AlGaN/AlGaN multiple quantum well (MQW) structures with well widths spanning from 1.65 to 5.0 nm under various excitations and temperatures. The samples were fabricated by migration-enhanced metal-organic chemical vapor deposition technique (MEMOCVD (R)). Screening of the built-in electric field by photogenerated carriers reduced quantum-confined Stark effect (QCSE). This is confirmed by solving the Poisson and Schrodinger equations for AlGaN-based quantum wells (QWs) under study. Analysis of the PL internal quantum efficiency under different excitations in MQWs with different widths shows strong influence of the carrier localization on the radiative properties of MQWs.

Place, publisher, year, edition, pages
2010. Vol. 207, no 2, 423-427 p.
Keyword [en]
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Physical Sciences
URN: urn:nbn:se:kth:diva-28689DOI: 10.1002/pssa.200925227ISI: 000275148400032ScopusID: 2-s2.0-76949104460OAI: diva2:390421
QC 20110121Available from: 2011-01-21 Created: 2011-01-19 Last updated: 2012-11-01Bibliographically approved
In thesis
1. 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.
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2012:18
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
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)
Swedish Research Council

QC 20121101

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

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