Analysis of the electron‐beam‐induced current of a polycrystalline p‐n junction when the diffusion lengths of the material on either side of a grain boundary differ

摘要

The short circuit current generated by the electron beam of a scanning electron microscope in p‐n junctions is reduced by enhanced recombination at grain boundaries in polycrystalline material. Frequently, grain boundaries separate the semiconductor into regions possessing different minority carrier life times. This markedly affects the short circuit current ISC as a function of scanning distance from the grain boundary. It will be shown theoretically that (a) the minimum of the ISC in crossing the grain boundary with the scanning electron beam is shifted away from the grain boundary toward the region with smaller life time (shorter diffusion length), (b) the magnitude of the minimum differs markedly from those calculated under the assumption of equal diffusion lengths on either side of the grain boundary, and (c) the minimum disappears altogether for small surface recombination velocities (s≪104 cm/s). These effects become however negligible for large recombination velocities s at grain boundaries. For p‐type silicon this happens for s≥105 cm/s.