The observation of damage regions produced by neutron irradiation in lithium-doped silicon solar cells

Abstract

Regions of lattice disorder produced in lithium-doped float-zone melted n/p-type silicon solar cells by irradiation with mono-energetic neutrons at doses between 10¹⁰ and 10¹³/cm² have been studied. The defect regions were revealed by chemically etching the surface of the solar cells and by observing carbon replicas in an electron microscope. It was found that the defect density increased with increasing irradiation dose and increased lithium content, whereas the average defect diameter was found to decrease. From thermal annealing experiments it was found that in the lithium-doped material the defect structure was stable at temperatures between 300 and 1200° K. This was found to be in contrast to the undoped material where at the lowest doses considerable annealing was observed to occur. The above results are discussed in terms of the theoretical predictions and models of defect clusters proposed by Gossick and Crawford and Cleland.