Light Trapping in Semiconductor Thin Film With Disordered Nanoholes

Finite-difference time-domain method is employed to investigate the optical properties of a semiconductor thin film patterned with circular holes. The presence of hole arrays, although reduces the amount of material usage, can greatly enhance the integrated absorption of the thin film. The optimal square hole lattice can enhance the integrated absorption by a factor of 5.6 over a bare thin film. It is also found that disorderness, including non-uniform radius and random position, can further enhance the absorption efficiency and broaden the absorption spectra. The effects of random position and non-uniform radius are found to be quite different: while absorption spectrum for thin film containing randomly positioned holes is almost broadband, the non-uniform hole radius only slightly broadens the absorption peaks of the periodic structures. The absorption enhancement in the disordered structure is attributed to the increased number of guided resonances in the structure. We also show that with carefully designed hole pattern the overall absorption can be further enhanced.