We demonstrate simultaneous lasing at two well-separated wavelengths in self-assembled InAs quantum-dot lasers, via ground-state (GS) and excited-state (ES) transitions. This effect is reproducible and strongly depends on the cavity length. By a master-equation model, we attribute it to incomplete clamping of the ES population at the GS threshold.

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In this paper, we present a systematic study of the effect of growth parameters on the structural and optical properties of InAs quantum dot ͑QD͒ grown under Stranski-Krastanov mode by molecular beam epitaxy. The dot density is significantly reduced from 1.9ϫ10 10 to 0.6ϫ10 10 cm Ϫ2 as the growth rate decreases from 0.075 to 0.019 ML/s, while the island size becomes larger. Correspondingly, the emission wavelength shifts to the longer side. By increasing the indium fraction in the InGaAs capping layer, the emission wavelength increases further. At indium fraction of 0.3, a ground state transition wavelength as long as 1.4 m with the excited state transition wavelength of around 1.3 m has been achieved in our dots. The optical properties of QDs with a ground state transition wavelength of 1.3 m but with different growth techniques were compared. The QDs grown with higher rate and embedded by InGaAs have a higher intensity saturation level from excitation dependent photoluminescence measurements and a smaller intensity decrease from temperature dependent measurements. Finally, single mirror light emitting diodes with a QD embedded in InGaAs have been fabricated. The quantum efficiency at room temperature is 1.3%, corresponding to a radiative efficiency of 21.5%.

Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. . These results should improve the usual quantum well (QW) laser performances, and finally allow the realisation, for example, of chirp-free directly-modulated lasers.However, more disruptive properties can also be explored with quantum dot lasers. In particular, it has been observed that above the ground state (GS) lasing threshold, the gain of the excited state (ES) is not clamped. Owing to the limited number of available GS levels, carriers injected in the ES cannot fully relax to the GS and contribute to increase the ES gain (carrier pile-up). This phenomenon is unique in the semiconductor laser domain, and leads to new device properties. Simultaneous lasing of two allowed transitions, respectively the ground state level transition and the excited state level transition has, for example, already been reported [3].In this Letter we have focused our investigation on a specific regime that appears at currents just below the ES threshold. In particular, we demonstrate that the GS filling implies giant linewidth enhancement factors (LEF) up to 60, far above any reported value for semiconductor lasers. As a result, purely frequency shift keyed (FSK) signal could be achieved by direct modulation of a semiconductor laser.After a brief description of the investigated device, we will present effective linewidth enhancement factor measurements, followed by dynamic measurements near the ES threshold.

Electrical transport in semiconductor superlattices is studied within a fully self-consistent quantum transport model based on nonequilibrium Green functions, including phonon and impurity scattering. We compute both the drift velocity-field relation and the momentum distribution function covering the whole field range from linear response to negative differential conductivity. The quantum results are compared with the respective results obtained from a Monte Carlo solution of the Boltzmann equation. Our analysis thus sets the limits of validity for the semiclassical theory in a nonlinear transport situation in the presence of inelastic scattering.

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Scollo, R. (2006). Two-state switching and dynamics in quantum dot two-section lasers. Journal of Applied Physics, 100 (11) Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publicationGeneral rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policyIf you believe that this document breaches copyright please contact us at:openaccess@tue.nl providing details and we will investigate your claim. The electrical control of the lasing wavelength in two-section quantum dot lasers is investigated. By changing the optical loss in the absorber section, the control of the ground-state ͑GS͒ and excited-state ͑ES͒ lasing thresholds and output powers is achieved. Additionally, a complex self-pulsation dynamics with simultaneous oscillations of the GS and ES intensities is observed. The experimental results are well explained in the framework of a rate equation model.