Complex, 3D Photonic Crystals Fabricated by Atomic Layer Deposition

Abstract

ABSTRACTRecently we have demonstrated the potential of Atomic Layer Deposition (ALD) for the fabrication of advanced luminescent photonic crystal (PC) structures based on the inverse opal architecture.[1–3] PC's offer efficiency enhancement, decreased threshold, and other enhancements that improve phosphor performance. 3D PC structures are being extensively modeled, revealing that changes in the structures such as shifting the distribution of dielectric material can significantly improve photonic band gap (PBG) properties. For example, in the inverted “shell” structure, the width of the PBG can be increased from 4.25% to 8.6%.[4] Similarly, the PBG width can also be increased to 9.6% by formation of a non-close-packed structure.[5] Using the FDTD method, we have found that the PBG in a TiO2 non-closed packed structure can be as high as 5%. The performance of these structures depends critically on precisely and accurately placed high dielectric material. Using ALD, we have demonstrated infiltration of TiO2 films with extremely smooth surfaces (0.2–0.4 nm RMS roughness) while maintaining a high level of control over the infiltration coating thickness, enabling formation of composite infiltrated and inverse opals with nano-scale precision.Here we report progress in fabrication of multi-layered and non-close packed PCs using ALD. Two and three-layer inverse opals were formed by the deposition of thin layers of ZnS:Mn and TiO2 in stacked configuration, each exhibiting luminescence when excited by UV light. Evidence for modification of the emission characteristics by high order PBGs (gaps other than between the 2nd and 3rd bands) has been observed. In addition, non-close packed inverse opals have been formed by infiltrating heavily sintered silica opals with TiO2, etching the spheres with hydrofluoric acid, and backfilling the resulting inverse opal. Resulting structures were characterized using specular reflectance and transmission, photoluminescence, and SEM. This work demonstrates the enormous potential that ALD offers for the realization of high performance photonic crystal structures.