Fabrication and replication of micro-optical structures for growth of GaN-based light emitting diodes

GaN light emitting diodes (LEDs) on sapphire substrates can be improved by micro-patterning substrate to perform epitaxial over-growth which drastically reduces defects' density in the light emitting region. We patterned Al 2O3 with focused ion beam and show a successful overgrowth of GaN. The exact shape of pattern milled into Al2O3 was replicated into a 0.4-mm-thick shim of Ni by electroplating. The surface roughness of Ni was ∼5:5 ± 2 nm and is applicable for the most demanding replication of nano-rough surfaces. This technique can be used to replicate at micro-optical elements Fresnel-axicons defined by electron beam lithography made on sub-1 mm areas without stitching errors (Raith EBL). Shimming of macro-optical elements such as car back- reflectors is also demonstrated. Ni-shimming opens possibility to make replicas of nano-textured small and large area patterns and use them for thermal embossing and molding of optically-functionalized micro-fluidic chips and macro-optical elements. © 2013 Copyright SPIE.