Thermal annealing performance of sulfur-hyperdoped black silicon fabricated using a Nd:YAG nanosecond-pulsed laser

- Effects of thermal annealing on properties of ns-laser-fabricated black Si were studied.
- Particles and protrusions overlying conical structures decreased after the annealing.
- Visible-light reflectance decreased by ∼2% owing to an increase of morphology smoothness.
- IR absorptance decreased slowly owing to a higher crystallinity and larger S doping depth.
- Sheet carrier concentration increased, whereas resistivity and sheet resistance decreased.

Compared to femtosecond-pulsed laser and ion implantation with chemical texturing methods, the nanosecond (ns)-pulsed laser method is inexpensive and efficient for fabricating a microstructured and hyperdoped crystalline silicon surface (usually known as black Si), facilitating the industrial manufacturing of optoelectronic devices. However, the ns-pulsed laser method has been rarely studied in material post-processing and device manufacturing. In this study, a microstructured and sulfur-hyperdoped p-type Si〈100〉 wafer surface was fabricated using a neodymium-doped yttrium aluminum garnet (Nd:YAG) ns-pulsed laser irradiation in sulfur hexafluoride gas. The effects of thermal annealing on the morphological, optical (visible and infrared (IR) spectra), and electrical properties of black Si samples were evaluated. The results show that the small particles and protrusions, overlying conical structures of the samples, decreased after the annealing. The light reflectance of the samples in the wavelength range 400-1000 nm decreased by ∼2%, and a high IR absorptance (λ = 1100-2400 nm) was observed. The IR absorptance decreased slowly from 86% to 60% with an annealing time of 30 (or 60) min and temperature increase from 575 K to 800 K (corresponding to the increase in diffusion length of S-dopant from 0.09 nm to 68.63 nm). Furthermore, sheet carrier concentration and resistivity of the black Si samples increased and decreased with increasing S-dopant diffusion length, respectively. The improvements in electrical property indicate that thermal annealing can enhance the activation of S-dopant and electrical rectification of the samples. These are important for developing Si-based broad-spectrum solar cells and IR detectors.

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