Impurity diffusion from uncoated foreign substrates during high temperature CVD for thin-film Si solar cells

In this paper, we study the diffusion of impurities from three types of for eign substrates (graphite, alumina and mullite) during thermal chemical vap our deposition (CVD) of a polycrystalline Si film. For this we use a rapid thermal CVD (RTCVD) system and characterization techniques such as secondar y ion mass spectroscopy (SIMS) and deep level transient spectroscopy (DLTS) . Results show that, in the case of materials like graphite, metallic conta minants can freely outdiffuse into the deposited layer and the environment. In contrast, the ceramic substrates release only a very limited amount of contaminants during the CVD process, making the need of a diffusion barrier much less severe. (C) 2000 Elsevier Science B.V. All rights reserved.