Analysis of phosphorus doped silicon oxide layers deposited by means of PECVD as a dopant source in diffusion processes
In order to increase the conversion efficiencies of silicon solar cells, advanced cell structures with selectively doped areas have received increasing interest. There is a strong need to separate the contacted diffusion profiles from the noncontacted. On the one hand, a high dopant concentration in the contact regime reduces the series resistance losses mainly due to lowered contact resistance. Additionally, recombination is reduced by shielding the minority charge carriers from surface at the contact. On the other hand, a low dopant concentration in the noncontact regime reduces the recombination losses and optimizes the spectral response of the cell. In this paper, phosphorus-doped silicon oxide layers are used as a diffusion source for tube furnace diffusion processes. It is shown that the sheet resistance of the diffused area is controlled by the silane gas flow during the deposition of phosphorus-doped silicon oxide. In order to analyze the influence of the diffused areas on the saturation current densities, symmetrical carrier lifetime samples are prepared. Therefore, a stack system consisting of a thermally grown silicon dioxide and silicon nitride is used for passivation purposes on textured samples.