Manipulations of light by ordered micro-holes in silicon substrates

Ordered micro-holes with controllable period, diameter and depth are fabricated in Si (001) substrates via a feasible approach based on nanosphere lithography. They dramatically reduce the reflectance in a broad wavelength range of 400-1000 nm, which can be deliberately modulated by tailoring their geometrical parameters. The simulated reflectance via finite-difference time-domain (FDTD) method agrees well with the experimental data. The FDTD simulations also demonstrate substantially enhanced light absorption of a Si thin film with ordered micro-holes. Particularly, the light-filled distributions around micro-holes disclose fundamental features of two types of modes, channel modes and guided modes, involving the wavelength-dependence, the origin, the dominant location region and the interference pattern of the light field around micro-holes. Our results not only provide insights into the antireflection and the substantially enhanced absorption of light by ordered micro-holes, but also open a door to optimizing micro-hole arrays with desired light field distributions for innovative device applications.