Splitting of absorptance peaks in absorbing multilayer backed by a periodically corrugated metallic reflector

The excitation of modes of an open-face slab waveguide by light incident on a thin-film photovoltaic solar cell with a periodically corrugated metal backreflector is indicated by peaks in the absorptance spectrum. An absorptance peak due to the excitation of a waveguide mode (WGM) can split as the corrugation depth increases. The splitting can be explained in terms of the wavenumbers of the WGMs of two open-face slab waveguides with different thicknesses of the semiconductor layer. The splitting of short-wavelength peaks occurs for smaller corrugation depths than the splitting of long-wavelength peaks, suggesting that the corrugations need not be very deep for optimal absorption of solar photons.