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.

Keywords:

• two-tier roughness
• wet chemical etching
• enhanced absorption
• bandgap

Acknowledgements

This work was partially supported by the National Science Foundation of China under grant No. 61 101 029. The authors would like to thank Zhenzhen Rao, Chuan Xin and Yaping Wang for their helps in SEM and XPS analysis and optical properties measurement.