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Photoexcited carrier trapping and recombination at Fe centers in GaN
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
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2016 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 21, article id 215706Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

Fe doped GaN was studied by time-resolved photoluminescence (PL) spectroscopy. The shape of PL transients at different temperatures and excitation powers allowed discrimination between electron and hole capture to Fe3+ and Fe2+ centers, respectively. Analysis of the internal structure of Fe ions and intra-ion relaxation rates suggests that for high repetition rates of photoexciting laser pulses the electron and hole trapping takes place in the excited state rather than the ground state of Fe ions. Hence, the estimated electron and hole capture coefficients of 5.5 x 10(-8) cm(3)/s and 1.8 x 10(-8) cm(3)/s should be attributed to excited Fe3+ and Fe2+ states. The difference in electron capture rates determined for high (MHz) and low (Hz) (Fang et al., Appl. Phys. Lett. 107, 051901 (2015)) pulse repetition rates may be assigned to the different Fe states participating in the carrier capture. A weak temperature dependence of the electron trapping rate shows that the potential barrier for the multiphonon electron capture is small. A spectral feature observed at similar to 420 nm is assigned to the radiative recombination of an electron in the ground Fe2+ state and a bound hole.

Place, publisher, year, edition, pages
American Institute of Physics Inc. , 2016. Vol. 119, no 21, article id 215706
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-190677DOI: 10.1063/1.4953219ISI: 000378923100053Scopus ID: 2-s2.0-84974605204OAI: oai:DiVA.org:kth-190677DiVA, id: diva2:953006
Note

QC 20160816

Available from: 2016-08-16 Created: 2016-08-12 Last updated: 2018-05-21Bibliographically 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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