Novel silicon surface passivation by porous silicon combined with an ultrathin Al₂O₃ film

We report on a dual passivation approach of monocrystalline-silicon (c-Si), which combines porous silicon (PS) treatment and pulsed laser deposition (PLD) of Al₂O₃ ultrathin layer. Al₂O₃ ultrathin films were deposited, under an oxygen background pressure of 10 mTorr. In this work we demonstrate that the dual treatment Al₂O₃/PS provide excellent passivation quality of c-Si surfaces. Surface passivation and reflectivity properties are investigated before and after heat treatment at 700 °C. The level of surface passivation is quantified using photoconductance and Fourier-transform infra-red absorption techniques. X-ray diffraction analysis suggested that the heat treatment leads to an average crystallite size decrease which help the diffusion of the Al₂O₃ NPs along the wafer surface. As a result, the effective minority carrier lifetime increases from 2 to 7 μs. Our results demonstrate that this dual treatment not only provides strong passivation of the c-Si substrate but decreases also the total surface reflectivity at 500 nm (from 28 % for untreated c-Si samples to ∼7 % for Al₂O₃/PS treated ones).