Enhanced etching rate of black silicon by Cu/Ni Co-assisted chemical etching process

In this paper, a new low cost Cu/Ni co-assisted chemical etching (Cu/Ni MACE) method was presented for fabrication of black silicon on diamond-wire-sawn multicrystalline silicon (mc-Si). The etching rate of Cu assisted chemical etching (Cu MACE) at room temperature was greatly improved by adding Ni ion solutions. A lowest average reflectivity of 10.33% in the range of wavelength 400-900 nm was obtained, with a decrease about 50% compared with that by the etching without Ni ions. The thickness reduction of the sample obtained by the Cu/Ni MACE was 3.5 times of the one of Cu MACE when ρ at 40% (ρ = HF/(HF+H2O2) the one prepared by the Cu MACE although the ρ (ρ = HF/(HF+H2O2), volume ratio) was changed with the former being about 3.5 times of the latter. Then, a tilted inverted pyramid-like structure was successfully achieved by one-step Cu/Ni co-assisted chemical etching in Si/Cu(NO3)2/NiSO4/HF/H2O2 solution followed by a further nano structure rebuilding treatment. Finally, tilted structure was proved to have better light trapping properties by simulation using the Finite-Difference Time-Domain (FDTD) method.