Effective suppression of nanotextured black silicon surface recombination channels by aluminum oxide: comparison from sputtered and ALD grown films

Abstract

Effective surface passivation of nano-textured silicon (NT-Si) using sputtered aluminum oxide (AlO x ) films is demonstrated and compared with the atomic layer deposition (ALD) grown AlO x films. Silver-assisted wet chemical etching is used to obtain sub-wavelength size features of black NT-Si, and then the NT-Si surface is chemically polished to minimize the surface defect states that act as trap centres for charge carriers. The NT-Si surface passivation is characterized by the density of interface trap states (D it) and the fixed charge density (Q f), which also correlate with the surface recombination rate (S eff). For the sputtered AlO x films, the estimated D it and Q f are ∼4 × 1011 eV−1 cm−2 and ∼7 × 1012 cm−2, respectively, yielding the S eff of ∼34 cm s−1. Whereas, for the ALD AlO x films the estimated D it, Q f, and S eff are ∼1.6 × 1011 eV−1 cm−2, ∼7.4 × 1012 cm−2, and ∼20 cm s−1, respectively. The chemical and field-effect passivation are evident for the ALD AlO x films with the reduced S eff. However, the sputtered AlO x films have shown only an indication of field-effect passivation with a small variation in the Q f. Still, the observed larger D it is due to the sputtering damage on the NT-Si surface compared to ALD AlO x films.