Silicon dioxide and silicon nitride as diffusion barrier for transition metals in solar cell applications

Crystalline silicon thin film (CSiTF) has a good potential for manufacturing cost effective solar cells. In order to take advantage of this potential inexpensive and therefore often highly impure substrates have to be used. If diffusing into the active silicon layer, impurities of the substrate may act as very efficient lifetime-killers in the electrically active layer and considerably reduce the solar cell efficiency. For this reason diffusion barrier layers are necessary to avoid contamination of the solar cell. Promising candidates for such barrier layers are, among others, SiO_2 and SiN_X. Therefore, the barrier efficiency of these materials at high temperatures is of utmost technological importance, albeit widely unknown. Investigations of the barrier efficiency of PECVD SiO_2 and SiN_X layers are presented in this paper. The diffusion of Fe and Cr in these materials is investigated by means of DLTS-measurements in source side and sink side FZ-silicon. Effective diffusivities are calculated from the data obtained by numerical analysis. SiN_X is found to be a considerably better barrier than SiO_2. (orig.)Available from: http://www.ise.fhg.de / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman