Abstract
The interactions between excitons, which are bosonic particles composed of an elec-tron and a hole bound by Coulomb interaction, and photons are greatly enhanced in waveguides where light is confined by total internal reflection. When the interaction is strong enough, the regime of strong coupling between the photonic mode of the guide and the excitonic resonance of the active layer is achieved, creating a quasi-particle known as an exciton-polariton, or simply polariton. These quantum fluids of light are attracting interest due to their potential applications in optoelectronics, particularly in so-called polariton lasers. With this in mind, this thesis focuses on the study, using spectroscopic methods, of polariton laser structures based on gallium nitride (GaN) in the waveguide geometry, which presents interesting specificities compared to the deeply investigated vertical cavity geometry. The main results of this work are (i) the demonstration of a polariton laser operating continuously at low temperature (70K). This laser exhibits an original mode of operation, resulting from the non-reciprocity between absorption and stimulated emission in the active layer. The significant gain allows for efficient operation on very short cavities, such as the 20μm-long cavities used in this study. Furthermore, a pump length of only 15% of the cavity length is suffi-cient to achieve the laser effect, clearly distinguishing these polariton lasers from con-ventional semiconductor lasers that require pumping a large portion of the laser cavity with a homogeneous active medium for gain to overcome losses; (ii) the observation, by extending our study to T=150K, of a transition in laser regime with a multimode character on a longer cavity of 60µm. Modeling of the measured spectra leads to the conclusion that this emission is pulsed, thanks to the formation of cavity solitons through mode locking induced by the nonlinear interactions between polaritons; (iii) preliminary electrical injection measurements in waveguides with doped injection lay-ers, following the implementation of a new electroluminescence experimental setup independent of that of optical spectroscopy.