Femtosecond laser doping of silicon: Electronic structure

Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The resulting textured surface is highly absorbing and looks black to the eye. The properties of this 'black silicon' make it useful for a wide range of commercial devices. In particular, we have been able to fabricate highly-sensitive PIN photodetectors using this material. The sensitivity extends to wavelengths of 1600 nm making them particularly useful for applications in communications and remote sensing. We have performed temperature-dependent resistivity measurements of silicon after doping with sulfur via femtosecond laser irradiation. Results are consistent with a theoretically predicted binding energy for sulfur donors of 100 meV below the conduction-band edge.