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Dynamic photon emission from multiphoton-excited semiconductor quantum dots
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
KTH, School of Biotechnology (BIO), Theoretical Chemistry.ORCID iD: 0000-0002-2442-1809
KTH, School of Biotechnology (BIO), Theoretical Chemistry.ORCID iD: 0000-0002-1763-9383
2008 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 9, 093703-1-093703-6 p.Article in journal (Refereed) Published
Abstract [en]

The dynamic process of multiphoton optical transitions in semiconductor quantum dots (QDs) has been studied by a Monte Carlo scheme. The scheme includes optical transitions of all electrons, initially occupying the valence-band confined states in the QD, among the confined states in valence and conduction bands. The optical transition probabilities are calculated by the time-dependent Schrodinger equation, and nonradiative phonon scattering processes have been included. Assisted by a two-photon excitation by a continuous-wave laser (one photon energy equals half of the QD energy band gap), an assembly of the QDs shows an emission peak around the band gap in the optical emission spectrum, while an ultrafast pulsed laser, whose photon energy is below the QD band gap, also induces a similar narrow but weaker emission peak, which results in a nonstrict multiphoton excitation condition for many potential applications including biophotonics. Extension of the theoretical study to the spherical CdS/Cd0.5Zn0.5S/ZnS-multicoated CdSe QD has reproduced the experimental absorption and multiphoton emission spectra.

Place, publisher, year, edition, pages
2008. Vol. 103, no 9, 093703-1-093703-6 p.
Keyword [en]
Electronic states; Laser pulses; Monte Carlo methods; Multiphoton processes; Photoexcitation; Semiconductor quantum dots; Valence bands; Optical emission spectra; Photon emission
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-8233DOI: 10.1063/1.2908187ISI: 000255983200072ScopusID: 2-s2.0-43949113666OAI: diva2:13498
QC 20100730. Uppdaterad från in press till published (20100730).Available from: 2008-04-18 Created: 2008-04-18 Last updated: 2010-07-30Bibliographically approved
In thesis
1. Optical Properties of Low Dimensional Semiconductor Materials
Open this publication in new window or tab >>Optical Properties of Low Dimensional Semiconductor Materials
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This dissertation presents a serial study on optical properties of different semiconductor materials. Three main types of studies are addressed: The role of doping levels of N and Al atoms in the room-temperature photoluminescence (PL) of 4H-SiC films for optoelectronic applications; the use of a basic Monte Carlo method combined with probability calculations of the time-dependent Schroedinger equation to manifest multi-photon absorption and emission of II-VI compound quantum dots (QDs) for bioimaging; a theoretical quantum chemistry approach to study of structure and optical properties of InGaAsN and GaAs clusters for laser technology applications. 4H-SiC films were grown on AlN/SiC(100) substrates by a chemical vapour deposition (CVD) system. Three well-defined room-temperature PL peaks close to the band-gap energy were observed. By a detailed theoretical analysis of optical transitions in the samples, it was found that the PL peaks are most probably due to the optical transitions between impurity levels and band edges, and the transition between the second minimum of the conduction band and the top of the valance band. Special attention has been paid to effects of doping levels of N and Al impurities. Optical transitions in several II-VI semiconductor QDs have been studied by a quantum Monte Carlo method. We model the QD energy band structure by a spherical square quantum well and the electrons in the conduction band and holes in the valence band by the effective mass approximation. The optical probabilities of optical transitions induced by ultrafast and ultraintense laser pulses are calculated from the time-dependent Schroedinger equation. With the inclusion of the nonradiative electron-phonon processes, the calculated absorption and emission spectra are in agreement with experimental work. The dynamic processes and up-conversion luminescence of the QDs, required for many applications including bio-imaging, are demonstrated. Quantum chemistry is used to study InGaAsN and GaAs nano systems. The molecular structures of a series of dilute-nitride zinc blende InGaNAs clusters are examined from the energy point of view with a semi-empirical method. The optimum cluster configurations are identified by which we can identify the detailed bonding structures and the effects of In mole fraction. After proper geometry construction, an effective central insertion scheme has been implemented to study the electronic band structures of GaAs at the first-principles level. The formation of energy bands and quantum confinement effects have been revealed, thus providing theoretical support for laser design.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 58 p.
Trita-BIO-Report, ISSN 1654-2312 ; 2008:8
Semiconductor, Low dimensional, optics
National Category
Physical Sciences
urn:nbn:se:kth:diva-4699 (URN)978-91-7178-909-9 (ISBN)
Public defence
2008-04-29, FA31, Roslagstullsbacken 21, AlbaNova, Stockholm, 14:00
QC 20100730Available from: 2008-04-18 Created: 2008-04-18 Last updated: 2010-07-30Bibliographically approved

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