Optically hyperdoped silicon

By irradiating silicon with a train of femtosecond laser pulses in the presence of chalcogen (column VI) compounds, a thin layer of Si is doped to previously unreported, non-equilibrium levels (about 2%). This optical hyperdoping (OHD) process creates a highly absorbing surface and extends silicon’s spectral sensitivity, even for infrared photons with energy less than the band gap. The optoelectronic properties of this 'black silicon' make it useful for a wide range of commercial devices in communications, remote sensing, and solar energy harvesting. Prototype OHD silicon photodiodes exhibit spectral responsivity at wavelengths up to 2 µm and strong photoconductive gain. The infrared response and photoconductive gain indicate that optical hyperdoping produces an entirely new class of materials.