Influence of the Etching Solution Composition on the Properties of Nanoporous Black Silicon Fabricated Via Aluminium-Assisted Chemical Etching

Aluminium-assisted chemical etching (AACE) process employs Al catalyst to synthesize nanoporous black silicon (b-Si). In this paper, the composition of the etching solution (hydrofluoric acid (HF) + hydrogen peroxide (H₂O₂) + deionized water (H₂O)) is varied to control the etching rate and hence the properties of the as-fabricated nanoporous b-Si. There is a significant variation in the surface morphology, the optical and electrical characteristics of the b-Si nanopores by varying the volume concentration of H₂O₂ (1–10 ml) in a fixed volume concentration (10 ml) each of HF and deionized water (H₂O). The b-Si nanopores exhibit an average depth of 436 nm, surface coverage of 45.2% and root mean square surface roughness of 35.7 nm when the nanoporous b-Si is fabricated by using Al catalyst thickness of 24 nm and chemical composition of HF-H₂O₂-H₂O (10–1-10 ml). The lowest value of average reflection (R_avg) from the surface of the as-fabricated nanoporous b-Si is 5.7% within 300–1100 nm wavelength range. The electrical parameters such as the sheet resistance, the hole mobility and the hole concentrations are 279.6 Ω/sq, 170 cm²/V.s and 3.33 × 10¹⁵ cm⁻³ respectively. A lower value of R_avg for the nanoporous b-Si is vital for photovoltaic (PV) cells and photosensor applications.