Tailoring Femtosecond‐Laser Processed Black Silicon for Reduced Carrier Recombination Combined with >95% Above‐Bandgap Absorption

The femtosecond‐pulsed laser processed black silicon (fs‐bSi) features high absorptance in a wide spectral range but suffers from high amount of laser induced damage as compared with bSi fabricated by other methods. Here, the aim is to minimize the charge carrier recombination in the fs‐bSi caused by laser damage as indicated by the sub‐bandgap absorption and as quantified by the carrier lifetime, while maintaining high absorption in the above bandgap. The effect of the laser parameters, including the focal position, the average power, and the scan speed are systematically studied by characterizing the surface morphology, the absorptance spectra, and the minority‐carrier recombination lifetime. For the surface passivation of fs‐bSi, the well‐established atomic layer deposited (ALD) Al 2 O 3 is used. The results show that with the tailored laser parameters, high average absorptance of about 96% in the visible range and minority carrier lifetime of 54 μs at the injection level of Δ n = 1 · 10 15 cm −3 can be obtained simultaneously. This work paves the way toward high‐performance broadband optoelectronic devices based on surface passivated fs‐bSi.