Large-scale fabrication of a simple cubic metal-oxide photonic crystal for light-trapping applications

Large-scale fabrication of a $TiO2$ three-dimensional photonic crystal with simple cubic (SC) geometry was demonstrated using semiconductor-processing techniques in a layer-by-layer method. Full exposure of 100 mm double-side polished silicon and fused silica wafers was performed using deep-UV projection lithography with a 1 $cm2$ field size, and a four-layer $TiO2/air$ crystal of lattice pitch $a=450$ nm was successfully realized. The authors have computed the iso-frequency surfaces (IFS) for this structure and for another, which is to be examined in a future work. The latter will consist of a $TiO2$ SC photonic crystal for which the air regions are filled in with luminescent material of refractive index $n=1.5$⁠. The IFS indicate that our $TiO2$ photonic crystal is capable of supporting parallel-to-interface refraction modes for normalized frequency as high as $∼1.0$⁠, and that these modes will persist should the dielectric contrast be lowered via infiltration of the air region. For characterization, integrating sphere reflection measurements were performed, and the results are compared with those obtained from finite-difference time-domain simulation.