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Intralevel transitions in quantum dots: development of far infrared quantum dot laser

Ziel

The main purpose of the present project is to develop an European research efforts on new types of infrared lasers based on intralevel (intersublevel) transitions of carriers in quantum dot (QD) structures. A new type of far-infrared emitter have been recently proposed and realized by the authors of the project. This emitter is based on intralevel optical transitions in quantum dots where efficient depopulation of the ground state of the QD is realized due to lasing in the near optical range. As opposite to spontaneous recombination, since lasing starts, all the nonequilibrium carriers recombine over limited number of energy levels and, thus the stimulated emission time can be reduced to subpicosecond range at currents sufficiently exceeding threshold. In other hand, the relaxation time from higher lying filled QD energy levels to the ground state remains sufficiently long due to lack of continuum states matching the LO-phonon energy. Thus the realization of population inversion for intralevel transitions can be easily realized. The spontaneous far-infrared emission in high power QD laser which is much more efficient than in a quantum well (QW) laser with similar parameters have been already observed by project authors.

The majority of the work of the project will be performed using the quantum dot structures grown by the participants of the project in Russia. To realize the far-infrared laser
i) InGaAs/GaAs structures with quantum dots of different size, shape and relative arrangement (uncoupled, vertically coupled) will be designed and grown. The theoretical and experimental investigations of far infrared emission and absorption in QD structures due to sublevel-sublevel and continuum-sublevel carrier transitions will be carried out. The optical pumping and current injection of electrons and holes into QD layers will be used. The results will be compared with reference QW structures. Characteristics of QD structures and carriers will be defined using experimental and theoretical study of processes of QD impact ionisation by hot electrons and holes in strong longitudinal electric field. The capture cross-section and ionisation rate will be determined;
ii) The edge emitting laser structures with composite wave guide will be specially designed for simultaneous generation of intraband FIR radiation due to intralevel transitions in QD and interband near infrared (NIR) radiation. Stimulated FIR and NIR radiation from lasers will be studied. The vertical cavity surface emitting lasers (VCSELs) based on QD with semiinsulating mirrors and intracavity contacts will be designed and created to investigate infrared emission completely avoiding free carrier absorption.

The experimental data for the different phenomena will be compared with the theory. The results of the experimental and theoretical work will be submitted as joint publications in the research journals and as presentations at international conferences.

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Institute for Semiconductor Physics
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Walter-Korsing Str. 2
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Letzte Aktualisierung: 30 Oktober 2002

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Permalink: https://cordis.europa.eu/project/id/INTAS-1997-00751/de

European Union, 2024