Foell, H. | Search NASA

NASA NTRS1984

The S-web Technique for High-speed Growth of Si Sheets

The support web (S-Web) technique which was conceived as a method to grow Si-ribbons at large areal growth rates is described. A net made from carbon fibers is pulled through liquid Si. Webs of liquid Si are drawn out within the meshes of the net and kept stable by the high surface tension of liquid Si. The liquid webs crystallize some time after their formation giving a ribbon shaped body of Si at high speed. Ribbons which are suitable for the fabrication of solar cells are obtained at low pulling speeds. The results of the net pulling experiments are presented.

Grabmaier, J. G.↗

NASA NTRS1984

A High-speed Characterization Technique for Solar Silicon

High-speed crystal growth techniques demand high-speed characterization techniques to allow a timely feed-back of information to the crystal growers. The unique properties of the Si electrolyte-contact (SEC) provide for an extremely fast and simple measurement of the light-induced photo-current for any piece of Si without lengthy preparation of the specimen. Electropolishing at high anodic current densities allows for insitu generation of fresh surfaces whereas preferential etching of defects in various modes is possible at low current densities. In n-type Si a simple estimation of the minority-carrier diffusion length is possible in many cases. Laser-scanning enables local probing of the photocurrent and provides data about the homogeneity of a sample. The experimental realization of the method is described in detail and examples are given and discussed.

Lehmann, V.↗