The contribution of planes, vertices and edges to recombination at pyramidally textured silicon surfaces

摘要

Summary form only given. 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 1.73-fold increase in Seff, UL. Second, the presence of {111}-oriented facets drives a 5-fold increase in Seff, UL at SiO2 passivated surfaces, but a small (1.5-fold) increase for SiNx passivation. A third factor, 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 Seff, UL when the pyramid period is 10 mm. At this period, it results in a negligible increase in Seff, UL at SiO2 passivated textured surfaces, but causes up to a 4-fold increase at the Si/SiNx interface. That the vertex/ridge density has minimal influence for oxide passivated surfaces is supported by the measurement of Seff, UL on samples with varying oxide thickness: stress at convex and concave features is known to increase with oxide thickness, but appears not to induce additional defects. Instead, it is the dominant {111} oriented surfaces that exhibit thickness dependent passivation quality. Finally, we found that Seff, UL is 1.2-1.5 times higher at inverted pyramid texture than at surfaces featuring a random arrangement of upright pyramids. The results of the present study, particularly for the Si/SiNx system, likely depend strongly on process conditions, but the methodology is universally applicable. We believe this to be the first study to distinguish the impact of {111} facets from those of vertices and edges; its novelty is pronounced among studies of the Si/SiNx:H system.