A tunable and scalable platform for visible high-contrast grating reflectors for micro-cavity LEDs

Pavel Shapturenka
Pavel Shapturenka
Engineering II - 1519

Applications in high-resolution displays for augmented and virtual reality, wearables, and ultra-small displays for portable electronics require ultra-small light emitting devices (micro-LEDs) to direct light upward towards the viewer, which requires auxiliary optical infrastructure such as a cavity. A low-cost, tunable, and scalable colloidal method was employed to demonstrate suspended TiO2 high-contrast grating (HCG) reflectors across the visible wavelength range for eventual integration as an output coupler in a micro-cavity LED. Silica particles of 400, 500, and 690 nm were used as a mask to form a quasi-ordered hexagonal hole array pattern that was transferred to a suspended TiO2 membrane ~200 nm thick. A static tunability of diffusely reflected wavelength was observed, corroborated by finite difference time domain (FDTD) simulations. As shown by simulation, further optimization of colloidal deposition and processing parameters is expected to improve the absolute reflectivity of the structure. The prototype structures obtained are promising for monolithic red-green-blue (RGB) elements for display pixels.