Femtosecond Laser Direct Writing Assisted Nonequilibriumly Doped Silicon n+-p Photodiodes for Light Sensing

Micronanostructured silicon surface is irradiated by femtosecond laser pulses at sulfur hexafluoride atmosphere (S-doped black silicon) and photodiodes are successfully fabricated based on this material. From the scanning electronic microscope and atomic force microscope images, the black silicon layer shows micro-nanocomplex structures (microcones covered with nanoparticles). The optoelectrical properties of n⁺-p junction are formed between S-doped micro-nanostructured silicon-layer and substrate after thermal annealing. For the n⁺-p photodiode, current-voltage characteristics at different incident light powers have been investigated. The responsivity for 800-nm wavelength is 0.69 A/W at -5 V reverse bias, which is close to that of the usual commercial Si p-i-n photodiode. The present devices are stable and well reproducible.