Photomagnetic investigations of grain boundaries in solar silicon

Abstract

A noninvasive approach to investigate grain boundaries in multicrystalline solar silicon is introduced. The technique is based on the magnetic detection of photogenerated charge carriers interacting with electrically active grain boundaries in the sample. The method is completely nondestructive and nonpolluting and uses highly sensitive superconducting quantum interference devices as detectors. It can be applied to solar silicon starting material as well as to processed wafers. Measurements on multicrystalline silicon fabricated by different methods are presented, showing distinct features of the magnetic signals, which can be associated with characteristic material properties such as the excess carrier diffusion length. Results of numerical simulations of the magnetic signals are discussed.