Near-unity below-band-gap absorption by microstructured silicon

We increased the absorptance of light by silicon to approximately 90% from the near ultraviolet (0.25 mum) to the near infrared (2.5 mum) by surface microstructuring using laser-chemical etching. The remarkable absorptance most likely comes from a high density of impurities and structural defects in the silicon lattice, enhanced by surface texturing. Microstructured avalanche photodiodes show significant enhancement of below-band-gap photocurrent generation at 1.06 and 1.31 mum, indicating promise for use in infrared photodetectors. (C) 2001 American Institute of Physics.