Omnidirectional reflector using a low refractive index material

Triple-layer omni-directional reflectors (ODRs) consisting of a semiconductor, a transparent quarter-wavelength dielectric layer and metal layer have high reflectivities at all angles of incidence. In this paper, triple-layer ODRs are demonstrated that incorporate nanoporous SiO₂, a novel low-refractive-index (low-n) material with refractive indices n ≪ 1.46 as well as dense SiO₂ (n = 1.46). GaP and Ag serve as the semiconductor and metal layer materials, respectively. An angle-integrated transverse electric (TE) mode reflectivity of R_avg|_TE = 99.9 % and transverse magnetic (TM) mode reflectivity R_avg|_TM = 98.9 % are calculated for the triple-layer ODRs employing nanoporous SiO₂. Reflectivity measurements, including the angular dependence of R, are presented. Novel hybrid ODRs consisting of semiconductor, a several micron thick low-n dielectric material layer, a distributed Bragg reflector (DBR) and metal layer have outstanding reflectivities for all incident angles. GaP and Ag serve as the semiconductor and metal layer, respectively. Nanoporous SiO₂ is used as the low-n material. TiO₂ and dense SiO₂ serve as the DBR materials. The angle-intergrated reflectivities of the TE and TM modes are calculated to be larger than 99.9% for the hybrid ODRs. The results indicate the great potential of the ODRs for light-emitting diodes with high light extraction efficiency.