GaN and ZnO are the backbone of two semiconductor families that share many physical properties: they are both wide bandgap materials with energy gaps in the UV region, they have large exciton binding energies (larger than the thermal energy at room temperature) as well as large oscillator strengths. Furthermore, alloyed with other elements (Al and In for GaN, and Cd and Mg for ZnO) they can cover a very large wavelength region, going from the infrared to the extreme UV, which has rendered GaN-based optoelectronic devices ubiquitous in our everyday life. Still, GaN optoelectronics suffer from a number of technological issues including the lack of adapted substrates, which leads to a large density of structural defects, and the generation of internal electric fields, which renders emission at both short and long wavelengths extremely challenging. In this talk I will first illustrate two approaches, based on the selective area growth of GaN by MOCVD, that we have implemented in CRHEA to overcome these difficulties.
In all GaN-based commercial devices active emitters are combined with photonic architectures that enable an accurate control of the photonic density of states around the emitter. These optical structures allow, for example, to enhance extraction efficiency or to achieve larger emission rates. In these situations the coupling between the emitter and the photonic environment can be treated as a small perturbation, the device operating in the so-called weak-coupling regime. If by some means the coupling strength between the emitters and their photonic environment is increased above a certain critical value, new mixed eigenstates termed exciton-polaritons dominate the behavior of the system, enabling to achieve optical nonlinearities orders of magnitude larger than in the weak-coupling regime. In the last part of the talk I will illustrate how we can exploit both coupling regimes and develop optoelectronic platforms allowing for new applications (e.g. detachable GaN-based microLEDs for biophotonics) as well as for studying exciting new physics, including the generation of fast propagation polaritons or operation close to an exceptional point.
Current research interests:
Head of the nanotechnology team in CRHEA-CNRS, my research interests include the growth of wide-bandgap semiconductors (GaN and ZnO) thin films and nanostructures, by MBE and MOVPE, and their integration into foreign substrates. Particular emphasis is made on the exploitation of these heterostructures on technologically-relevant photonic devices (e.g. VCSELs or LEDs) as well as in more fundamental physics (polaritons, quantum optics).
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