Optical and electronic properties of MAE textured nanoporous silicon

Abstract

We present a 3-step metal-assisted chemical etching (MAE) texturing technique to fabricate nanoporous Si (MAE nSi) using mono- and multi-crystalline silicon (mc-si) substrate. We show that only a very short etch back is necessary to obtain low reflectance. The angular distribution of the reflected light suggests that most of the losses due to the surface reflectance can be recovered after encapsulation and this has been validated in this work. We demonstrate that by using the texturing method shown in this work, very low reflectance can be achieved upon encapsulation. The substantial reduction in reflectance, for some of the textures, upon encapsulation may be partly attributed to the angular distribution of light reflected from the textured surface. Texturing is shown to result in a modest increase in the surface area. However, the increase in the surface recombination rate is smaller than the increase in the surface area, and typically significantly less than a factor of 3, when samples are passivated with atomic layer deposited Al2O3. This result suggests neither the local curvature nor the predominant crystallographic orientation causes additional recombination at the MAE nSi surface. The combination of low surface reflectance and low surface recombination of the MAE nSi makes it a very interesting candidate for solar cell applications.