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On the Surface Passivation of Textured C-Si by PECVD Silicon Nitride

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2 Author(s)
Yimao Wan ; Res. Sch. of Eng., Australian Nat. Univ., Canberra, ACT, Australia ; McIntosh, K.R.

We investigate the surface passivation of crystalline silicon (c-Si) wafers that are textured with random upright pyramids and passivated with amorphous silicon nitride (SiNx). Over a large range of refractive indices (n = 1.89-4.1 at 632 nm), we achieve a low upper limit to surface recombination velocity on textured samples (Seff,UL <; 10 cm s-1 at an excess carrier density of 1015 cm-3). We also find that Seff,UL is higher for textured surfaces than for planar surfaces when the NH3:SiH4 ratio is high (and, hence, n is low). For example, when passivated by an N-rich SiNx deposited with NH3:SiH4 = 4.7 (n = 1.83), the vertices and/or edges of the pyramidal texture drives a 3.5 times increase in Seff,UL. As the NH3:SiH4 ratio decreases (and n increases), Seff,UL of the textured surfaces decreases rapidly and approaches the same Seff,UL as the planar surfaces when NH3:SiH4 ≤ 0.7 ( n ≥ 2.3). By contrast, we find that irrespective of NH3:SiH4 ratio, and, therefore, n, Seff,UL is equivalent on {100} and {111} planar surfaces. The results indicate that the increase in Seff,UL of the textured surfaces is related to the presence of vertices and/or edges of the pyramids rather than to the presence of {111}-orientated facets. By depositing varying degrees of corona charge on the samples, it is found that the increase in recombination introduced by 1) a higher NH3:SiH4 ratio and 2) the vertices and edges of the pyramids is primarily due to an increase in defect density rather than a decrease in SiNx charge density.

Published in:

Photovoltaics, IEEE Journal of  (Volume:3 ,  Issue: 4 )