Absorption Modulation, Enhancement, and Narrowing Using Sub-Wavelength Gratings

The Sub-Wavelength Grating (SWG) has great potential to be used as a substrate in narrowband photodetectors of an adjustable detection range covered visible and near-infrared spectrum. By the combination of polycrystalline MAPbI3 perovskite material and a specially designed SWG substrate, the absorption spectrum of perovskite material at specific wavelengths within inherently weak band-edge absorption would be enhanced due to guided-mode resonance effect, resulting in a modulated, enhanced, and narrowed absorption of perovskite material. We designed different parameters of SWGs to evaluate the absorption of perovskite within the bandgap of perovskite. The influences of depth, periodicity and fill factor are systematically studied using finite-difference time-domain (FDTD) simulation method. Finally, we achieved a double enhancement of absorption at 780 nm for SWG-perovskite sample compared with planar counterpart at which wavelength normally negligible absorption is witnessed. Moreover, we fabricated the designed SWG substrate and successfully deposited and infiltrated polycrystalline MAPbI3 perovskite material on it.