Experimentally measured optical properties of photonic crystal LEDs are reported here. Photonic crystal and photonic quasi-crystal structures were fabricated on GaN epilayer LED wafer material using both direct-write electron beam lithography and nanoimprint lithography. Some of these structures were processed to make finished LEDs. Both electroluminescence and photoluminescence measurements were performed on these structures. Devices were characterized for their current-voltage characteristics, emission spectra, far-field emission pattern, and angular emission pattern. These results are useful for fabricating photonic crystal LEDs and assessing their operational properties.

a b s t r a c tWe describe a comparison of nanofabrication technologies for the fabrication of 2D photonic crystal structures on GaN/InGaN blue LEDs. Such devices exhibit enhanced brightness and the possibility of controlling the angular emission profile of emitted light. This paper describes three nano lithography techniques for patterning photonic crystal structures on the emitting faces of LEDs: direct-write electron beam lithography, hard stamp nanoimprint lithography and soft-stamp nanoimprint lithography with disposable embossing masters. In each case we describe variations on the technique as well as its advantages and disadvantages. Complete process details have been given for all three techniques. In addition, we show how high performance GaN dry etch techniques, coupled with optical process monitoring can transfer resist patterns into underlying GaN material with high fidelity.

This paper describes the formation of mono-domain highly ordered nanoporous alumina on the scale of a 2 inch diameter silicon wafer by anodization of aluminium evaporated on a patterned SiO(2) mask on a silicon substrate. The position of the ordered pores correlates with holes in the SiO(2) mask, which guide the electric field during anodization and initiates pore nucleation. The technique is suitable for the production of ordered nanoporous alumina on a wafer scale and overcomes the time, cost and scale limitations of existing processes.

Anodic porous alumina nanostructures have been fabricated with tapered and cylindrical pores with a spacing of 100 and 200 nm and depth of 180-500 nm. The porous nanostructures were replicated into polymer films to create a moth-eye anti-reflecting surface by a roll-to-roll UV replication process. The angle dependent optical transmission of the resulting polymer films exhibited up to a 2% increase in transmission at a normal angle and up to a 5% increase in transmission at a 70° angle of incidence to an equivalent film with a surface replicated from polished aluminum. No significant difference was observed between the optical performance of moth-eye surfaces formed from cylindrical and tapered nano-pores.

In this paper we discuss theoretical modelling methods for the design of photonic crystal and photonic quasi-crystal (PQC) LEDs - and apply them to the analysis of the extraction enhancement performance and shaping of the emitted beam profile of PQC-LED structures. In particular we investigate the effect of the pitch of the PQC patterning, and consider the physical mechanisms giving rise to performance improvements. In addition, we examine the relative contributions to performance improvements from effective index reduction effects that alter the conditions for total internal reflection at the device air interface, and from photonic crystal scattering effects that give rise to radically improved extraction performance. Comparisons are made with the performance of recently fabricated devices