Analysis of the Atomic Layer Deposited Al2O3 field-effect passivation in black silicon

• Excellent surface passivation quality is demonstrated in n-type black silicon.
• High aspect ratio structures show no crystallographic damage.
• Black silicon is much more sensitive to surface charge than planar silicon.
• The larger surface area due to nanotexturing does not increase surface recombination.

We demonstrate that n-type black silicon can be passivated efficiently using Atomic Layer Deposited (ALD) Al2O3, reaching maximum surface recombination velocities below 7 cm/s. We show that the low surface recombination velocity results from a higher sensitivity of the nanostructures to surface charge and from the absence of surface damage after black silicon etching. The surface recombination velocity is shown to be inversely proportional to the fourth power of the negative charge in contrast to the quadratic dependence observed in planar surfaces. This effect compensates the impact of the increased surface area in the nanostructures and extends the potential of black silicon for instance to n-type Interdigitated Back Contact (IBC) cells.