Effects of substrate resistivity and different etching times toward broadband absorption enhancement in black silicon synthesized by metal-assisted chemical etching (MACE)
摘要
Black silicon (b-Si) is a promising material for photovoltaic and optoelectronic applications owing to its broadband light absorption. This study investigates b-Si nanopillars fabricated by one-step metal-assisted chemical etching (MACE) on two p-type (100) silicon substrates with different resistivities. Hall-effect measurements were used to correlate resistivity, carrier concentration, and mobility with nanopillar morphology and optical response. The high-resistivity sample S1 (2.70 ± 0.85 Ω·cm, 2.47 × 1016 cm−3, 157.0 cm2/V·s) produced a more uniform nanopillar structure (796.9 nm depth, 54.3% coverage, 41.6 nm roughness) and reached an average reflectance of 9.3% at 20 min. In comparison, the heavily doped sample S2 (0.009 ± 0.012 Ω·cm, 1.08 × 1019 cm−3, 337.3 cm2/V·s) etched faster, forming deeper nanopillars (920.4 nm) with an average reflectance of 10.3% at 30 min, but exhibited less uniform morphology and stronger free-carrier absorption in the near-infrared. An electro-optical figure of merit, incorporating normalized absorption, weighted average reflectance, and carrier concentration, indicated superior overall performance for S1. These results show that nanopillar morphology primarily governs light trapping, whereas substrate resistivity and carrier concentration determine the extent to which optical gains are preserved, highlighting high-resistivity silicon as a more favorable platform for broadband b-Si design.