Quantum dots and photonic crystals for white light generation and extraction in gallium nitride-based LEDs

This thesis investigates the possibility to use two-dimensional (2D) photonic crystals (PhCs) fabricated by nano-imprint lithography (NIL) to increase the extraction of multiple-wavelength guided modes (or guided white-light) outside of semiconductor or hybrid inorganic/organic (polymer) planar layers with refraction indices > 1 containing light-emissive components, pumped optically (such as colloidal quantum dots (QDs)) or electrically (such as GaN/InGaN quantum wells (QWs)).; The optical properties of InGaP colloidal QDs into different matrices were studied. These efficient light-emitting species are prone to oxidation and methods to improve their passivation are presented. White-light was generated by combining red and green-emitting CdSe/ZnS core/shell colloidal QDs in PMMA polymer films simultaneously pumped by blue-emitting GaN LEDs.; Numerical simulations were used to show that when positioned in or in the vicinity of planar layers or optical cavities, a large part of the light emitted from horizontal or vertical oscillating dipole sources is propagating only inside the layers, and is progressively attenuated there when absorbing layers are present. Other numerical simulations demonstrated the potential of 2D PhCs to extract most if not all of the guided modes.; Processing steps used for the fabrication of large-area 2D PhCs making use of NIL and dry-etching are described. Results collected from a broad set of samples including 2D PhCs, both photoluminescent (PL) and electroluminescent (EL), are presented. Angular-resolved PL and EL measurements demonstrate that 2D PhCs etched into MOCVD-grown GaN layers on sapphire substrates can efficiently extract guided modes emitted from GaN/InGaN QWs and from colloidal QDs. Damage-free 2D PhCs integration was proposed and implemented using the self-assembly property of TiO2 sol-gel precursors onto polymer layers patterned by NIL on MOCVD-grown GaN layers on sapphire. This allowed to demonstrate an enhancement in light extraction of 100%. Light extraction from colloidal QDs/PMMA thin films was also enhanced, 10 to 40% increase, depending on the films and PhCs parameters. Effective extraction lengths of guided modes in GaN layers were measured by micro-PL and ranged between 50 and 200 mum depending on the wavelength of light.