Optical Absorption Properties of Semiconducting Nanostructures with Different Shapes

In this study, a detailed experimental and theoretical investigation of optical absorption properties of indium sulfide (In2S3) nanostructure arrays in different shapes are presented. Zigzags, springs, screws, tilted rods, and vertical rods of In2S3 are grown using a glancing angle deposition (GLAD) technique. Nanostructured coatings are of similar material volume and porosity, yet with different shapes. Total optical reflection, transmission, and absorption profiles of In2S3 nanostructures are obtained by UV-vis-NIR spectroscopy using an integrating sphere. Measurements reveal that optical absorption of semiconducting nanostructures can strongly depend on their shapes. Under normal incidence of light, 3D geometries such as springs, screws, and vertical rods can provide enhanced absorption compared to zigzags, and tilted rods. Results of finite difference time domain (FDTD) simulations predict that spring, screw, and tapered-rod shapes can introduce a uniform distribution of diffracted light intensity and stronger absorption within the nanostructured layer, indicating an enhanced diffuse light scattering and light trapping. Zigzags and tilted rods show a relatively weaker absorption, similar to the experimental results. Experimental and simulation results are also compared to the predictions of effective medium theory. Current effective medium approximations are not sufficient to explain the high optical absorption of the nanostructures.