Local investigation of recombination at grain boundaries in silicon by grain boundary-electron beam induced current

Grain boundary-electron beam induced current (GB-EBIC) is an alternative EBIC geometry without a Schottky contact or pn junction but with ohmic contacts on either side of a GB. The GB itself acts as a charge collecting plane. We developed this EBIC mode both experimentally and theoretically. We calculated the current profiles with the diffusion length and the recombination velocities of the GB and the surface as parameters by solving the three-dimensional diffusion problem. The influence of different diffusion lengths at both sides and the angle between GB and surface is discussed. By variation of the injection level and application of an external bias local current voltage characteristics of the GB are obtained from which change of the local barrier height with increasing injection level can be deduced. We can describe the measured recombination behavior by an electronic GB model with a double depletion layer and deep interface states in a detailed balance approach. We applied this EBIC mode to grain boundaries in solar cell silicon and observed significant variations of the local recombination behavior and the diffusion length along a single GB.