| Summary: | The ability to fabricate semiconductor wafers with spatially selected regions of different bandgap material is required for the fabrication of monolithic photonic integrated circuits (PIC's). Although this subject has been studied for three decades and many semiconductor engineering approaches have been proposed, the problem of achieving reproducible results has constantly challenged scientists and engineers. This concerns not only the techniques relaying on multiple sequential epitaxial growth and selective area epitaxy, but also the conventional quantum well intermixing (QWI) technique that has been investigated as a post-growth approach for bandgap engineering. Among different QWI techniques, those based on the use of different lasers appear to be attractive in the context of high-precision and the potential for cost-effective bandgap engineering. For instance, a tightly focused beam of the infrared (IR) laser could be used for the annealing of small regions of a semiconductor wafer comprising different quantum well (QW) or quantum dot (QD) microstructures. The precision of such an approach in delivering wafers with well defined regions of different bandgap material will depend on the ability to control the laser-induced temperature, dynamics of the heating-cooling process and the ability to take advantage of the bandgap engineering diagnostics. In the frame of this thesis, I have investigated IR laser-induced QWI processes in QW wafers comprising GaAs/A1GaAs and InP/InGaAsP microstructures and in InAs QD microstructures grown on InP substrates. For that purpose, I have designed and set up a 2-laser system for selective area rapid thermal annealing (Laser-RTA) of semiconductor wafers. The advantage of such an approach is that it allows carrying out annealing with heating-cooling rates unattainable with conventional RTA techniques, while a tightly focused beam of one of the IR lasers is used for `spot annealing'. These features have enabled me to introduce a new method for iterative bandgap engineering at selected areas (IBESA) of semiconductor wafers. The method proves the ability to deliver both GaAs and InP based QW/QD wafers with regions of different bandgap energy controlled to better than « 1nm of the spectral emission wavelength. The IBESA technique could be used for tuning the optical characteristics of particular regions of a QW wafer prepared for the fabrication of a PIC. Also, this approach has the potential for tuning the emission wavelength of individual QDs in wafers designed, e.g., for the fabrication of single photon emitters. In the 1st Chapter of the thesis, I provide a short review of the literature on QWI techniques and I introduce the Laser - RTA method. The 2nd Chapter is devoted to the description of the fundamental processes related to the absorption of laser light in semiconductors. I also discuss the results of the finite element method applied for modeling and semi-quantitative description of the Laser - RTA process. Details of the experimental setup and developed procedures are provided in the 3rd Chapter. The results concerning direct bandgap engineering and iterative bandgap engineering are discussed in the 4th and 5th Chapters, respectively.
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