High near infrared absorption of hyper-doped silicon induced by co-doping of sulfur and nitrogen

In this paper, we investigate the dependence of NIR absorption of hyper-doped silicon on different sulfur and nitrogen doping ratio. With different molecular proportion of N₂ and SF₆ background gas, femtosecond laser irradiation was used to implant co-doping of sulfur and nitrogen into silicon. The hyper-doped silicon presents high absorption properties in NIR and visible range. The results of first-principles calculations demonstrate the high absorption in NIR is ascribed to the induced impurity energy levels in hyper-doped silicon. The nitrogen doping process improves the crystallinity in the doped layer because the doped nitrogen repairs defects in silicon lattices. Given the thermal stability of nitrogen, the co-doping dopants limit the diffusion of sulfur during the annealing process. The co-doping process proposed in this paper provides a method to fabricate high performance NIR silicon optoelectronic device.