Grain boundaries in semiconductors

Abstract

This review presents the available experimental and theoretical understanding on the structure and electronic properties of grain boundaries in semiconducting materials. High-resolution electron microscope images of interfaces are interpreted within the framework of the structural unit model of grain boundaries, and the electronic properties of the grain boundaries discussed with relation to the popular symmetric Schottky barrier model for charge trapping and potential barrier formation. It is shown that these models give some limited understanding of the physical processes that occur at grain boundaries in elemental semiconductors, but that in compound semiconducting materials the effects of non-stoichiometry at the boundary regions must also be considered. Segregation of impurity and dopant species to the boundaries can have significant influence on their electrical properties, and the question of what structural or chemical features are responsible for the observed properties is posed. Diffusion at semiconductor grain boundaries is also discussed, and finally the electrical properties of zinc oxide varistor material are presented in the light of the models of carrier interactions with grain boundaries.