Enhanced ultraviolet to near-infrared absorption by two-tier structured silicon formed by simple chemical etching

Abstract

Two-tier structured silicon with micron/nanometre scale features is fabricated by simple wet chemical etching. The structured silicon sample exhibits dramatically enhanced absorption from ultraviolet to near-infrared wavelength (250–2500 nm). Absorption is enhanced to near unity at wavelengths shorter than 1100 nm caused by the extremely suppressed reflection from the two-tier structured surface. Within the wavelength range from 1100 to 2500 nm, the sample exhibits a strong absorbance of 69.6% at 1100 nm and an average of 30% at longer wavelengths. By analyzing XPS spectra from the surface of the two-tier structured sample, we attribute this near-infrared absorption to band structure and morphological changes presented in the textured layer.