The Contribution of Planes, Vertices, and Edges to Recombination at Pyramidally Textured Surfaces

We present a methodology by which one may distinguish three key contributors to enhanced recombination at pyramidally textured silicon surfaces. First, the impact of increased surface area is trivial and equates to a √3-fold increase in S_eff,UL. Second, the presence of {1 1 1}-oriented facets drives a fivefold increase in S_eff,UL at SiO₂-passivated surfaces but a small (1.5-fold) increase for SiN_x passivation. A third factor, which is often proposed to relate to stress at convex and concave pyramids and edges, is shown to depend on pyramid period (and, hence, vertex/ridge density). This third factor impacts least on S_eff,UL when the pyramid period is 10 μm. At this period, it results in a negligible increase in S_eff,UL at SiO₂ -passivated textured surfaces but causes at least a sevenfold increase at the Si/SiN_x interface. Finally, we found that S_eff,UL is 1.5-2.0 times higher at inverted pyramid texture than at surfaces featuring a random arrangement of upright pyramids. The results of this study, particularly for the Si/SiN_x system, likely depend on process conditions, but the methodology is universally applicable. We believe this to be the first study to distinguish the impact of {1 1 1} facets from those of vertices and edges. Further, we find that {1 1 1} surfaces, rather than vertices and edges, are chiefly responsible for the poor-quality passivation achieved by thick oxides on textured surfaces.