Microscopic description of tunnel-injection quantum-dot lasers

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The goal of this project is to advance the design of semiconductor lasers, which have the potential to strongly improve fiber-based optical data communication as used for the internet. The design is based on a tunnel-injection (TI) structure with quantum dots (QDs) as active material and promises strongly improved modulation speed. The challenge for the design lies in the interplay between different nanostructure components: the inhomogeneously broadened QD ensemble, the TI barrier, and the bulk barrier material used for carrier injection. The physics underlying such a device has several demanding aspects. Carrier transport connects three-, two-, and zero-dimensional structures, the carrier scattering processes between these structures is governed by many-body effects, and the device performance depends on the interplay between carrier dynamics and gain properties in the presence of a tunnel barrier. A consortium of leading scientists in this field, represented by Johann Peter Reithmaier (Univ. Kassel), Grzegorz Sęk (Wroclaw University of Technology) and Gadi Eisenstein (Technion, Israel Institute of Technology) is presently working on the experimental realization of high-speed TI-QD lasers and their characterization with various spectroscopic methods. The applicant has been invited to join this consortium and the structural goal of this project is to establish the framework for a new direct collaboration with all three groups. In the first funding period, new and unexpected results for the physics of TI-QD-lasers were discovered. The LO-phonon resonance condition for the alignment of QD levels turns out to be suspended by electronic state mixing in the nanostructure and many-body effects (polarons). Instead, a spectral filter effect of the TI-barrier was discovered. Only with proper alignment of this spectral filter to the inhomogeneous broadening distribution of the QD emitters the improved modulation properties of TI-QD lasers are expected. According to these new insights, during the second application period, new laser structures will be grown and characterized. In parallel, theoretical models will be expanded to conduct direct experiment-theory comparisons. Our goal is a microscopic understanding of the relevant physics underlying the device operation in TI-QD lasers and the demonstration of improved emission processes.