Couplage du séléniure de gallium bidimensionnel à des cavités plasmoniques

2D materials have long been the focus of intense research activities due to very interesting properties arising from quantum confinement. Gallium selenide (GaSe) is one such material that has received interest, in part due to its very strong nonlinear optical properties and also for spintonic applications. It has an anisotropic band structure with an out of plane dipole transition which makes it an excellent candidate for use in plasmonic nanocavities. These cavities are used to enhance the photoluminescence (PL) emission of emitters embedded in them, and could be used to more effectively detect PL from ultrathin GaSe which has a very weak emission in part due to its out of plane transition. The main objective of this project was to couple ultrathin GaSe to plasmonic nanocavities. Firstly, we investigate the PL properties of a GaSe crystal and from mecanically exfoliated GaSe flakes. Measurements on a GaSe crystal show a superquadratic PL dependance with excitation power for small excitation powers. Measurements with a pulsed laser show a biexponential decay of PL intensity with values ranging from �tc = 0.25 − 1.1 ns for the short lifetime and t�l = 1 − 5 ns for the long lifetime. Temperature dependant measurements have shown a superquadratic dependance as function of excitation power for all temperatures ranging from 80 K - 296 K. PL measurements on GaSe flakes show a superlinear power dependance at the same excitation powers as well as lifetimes ranging from t�c = 40 − 230 ps and t�l = 0.2 − 1 ns. A modelisation of the recombination processes in GaSe has been completed to explain the superquadratic PL intensity as function of excitation power for the GaSe crystal. Pumping of electrons to the M point of the lowest conduction band and then transfer of these electrons to the T point is a key ingredient to obtain superquadratic dependance. The presence of defect levels and trapping of electrons and holes is also a key ingredient, and is shown to greatly affect the recombination processes. The amplification of luminescence of an emitter in a plasmonic nanocavity was investigated using the finite elements method. The wavelength of the fundamental plasmonic mode is shown to increase with nanocube length, decrease with gap thickness and increase with refractive index in the cavity. Also, the amplification factor at resonance is shown to increase with nanocube length, decrease with gap thickness and decrease with refractive index in the cavity. The redirection of the emission due to plasmonic cavity is also shown using simulations. Finally, the coupling of plasmonic nanocavities with GaSe was experimentally realised with dAg = 75±10 nm silver nanocubes, a eAu � 75 nm thick gold layer and exfoliated GaSe flakes. An enhancement factor of EF = 7.4 ± 0.2 was measured.