Shape and size dependence of the anti-reflective and light-trapping action of periodic grooves

The shape and size dependence of the anti-reflective and light-diffusing properties of surfaces with linear periodic grooves is studied. Grooves of triangular or rectangular cross-sections on the front or back surface of a crystalline silicon layer are considered. Our method is an extension of the rigorous, two-dimensional, coupled-wave, electromagnetic analysis of TE modes in dielectric relief gratings to the case of multilayer systems with both TE and TM modes through the use of a generalized transfer matrix formalism. Surfaces with shallow, sub-micrometre rectangular grooves have substantial anti-reflective and light-diffusing actions contrary to geometric optics results. Surfaces with sub-micrometre triangular grooves are less efficient anti-reflectors and light diffusers than we expect from geometric optics predictions, which are slowly approached as the period increases. Light diffusion is totally absent for grooves of either types with a period Lambda < 0.2 mum. Front-surface rectangular grooves of period 0.65 mum and height 0.2 mum lead to an absorbance enhancement in the infrared part of the solar spectrum comparable to that achieved with practical 70.5degrees triangular grooves. Back-surface rectangular grooves lead to some improvement compared with flat surfaces, but are somewhat inferior to back-surface triangular grooves. Copyright (C) 2002 John Wiley Sons, Ltd.