Light trapping by formation of nanometer diameter wire-like structures on μc-Si thin films

The electrochemical formation of porous silicon (PS) layers on microcrystalline silicon (μc-Si) thin films in HF-based solutions was investigated. The thickness of such PS-layers is as small as 50 nm which we suggest may have application in light trapping structures for Si solar cells. The integrated reflectance in the visible spectral region was reduced to less than 10%, depending on the etching conditions for PS-formation. Scanning electron microscopy reveals a nanometer size wire-like structure. The photoluminescence (PL) intensity increases and the PL maximum shifts to longer wavelength with increasing length of the wires. In addition, electron microscopy shows that the volume of the crystallites is preferentially etched but not the grain boundaries. This etching effect point to a potential loss across or along these grain boundaries which reduces the etching rate, thus leading to the wire-like structure.