Internal omni-directional reflector using a low refractive index material for light-emitting diodes

A triple-layer omni-directional reflector (ODR), which consists of a semiconductor, a transparent quarter-wavelength dielectric layer, and a metal layer, has high reflectivity at all angles of incidence when used as an internal ODR. In this paper, triple-layer ODRs are demonstrated that incorporate nanoporous SiO₂, a new low-refractive-index (low-n) material with refractive index ≪1.46. Internal reflectivity measurements, including the angular dependence of R, are presented. The angle-integrated TE/TM-averaged reflectivity of the triple-layer reflector using nanoporous SiO₂ is 99.4 %. This is the highest ever reported averaged reflectivity for an internal ODR. The mirror loss of the triple-layer ODR is a factor of 7 lower than the mirror loss of conventional metal reflectors. The results indicate the great potential of the ODR for light-emitting diodes with high light-extraction efficiency.