Photoconductance transient response in polycrystalline silicon

The photoconductance transient response in polycrystalline silicon has been studied theoretically and experimentally. Shockley-Read-Hall statistics are used to describe the emission and capture processes at the grain-boundary traps. Under appropriate conditions, the minority carrier capture and emission time constants of the grain-boundary trap can be directly obtained from the photoconductance transient response. The photoconductance method is therefore useful for studying grain-boundary deep level states. The special case when a focused laser spot is employed is also discussed. From the experimental data obtained from large-grain Wacker polycrystalline silicon, we have discovered a donor-like level at 0.48 eV below the conduction band with a concentration of 2×10¹⁰ cm^-2. The electron (minority carrier) lifetime is found to be about 6×10^{- 10}-10^-9 s.