Conductance of silicon grain boundaries in as‐grown and annealed bicrystals

The conductivity across the grain boundary plane was investigated on p‐type silicon bicrystals. A correlation was found between the electrical properties and the crystallographic structure for boundaries with the coincidence structures Σ9, 13, 25, 27, and for noncoincidence orientations with Σ>100. The boundaries were analyzed using electron beam induced current (EBIC) (minority carriers) and conductance measurements (majority carriers). The influence of a vacuum heat treatment (850 °C, 30 min) was studied for the different grain boundary structures. This was compared with an annealing at 850 °C in a POCl3 atmosphere as used in the solar cell diffusion step. A narrow band centered respectively at 0.14 and 0.10 eV above the valence band is proposed to explain the experimental behavior of the Σ25 and 27 boundaries.