Abstract: In the particular embodiments of the invention disclosed in the specification, a single crystal silicon plate having heavy metal impurities is coated with a layer of amorphous silicon several hundred to several thousand Angstroms thick in a vacuum vessel by a glow discharge at a pressure of 1 to 10 Torr and a temperature of about 200.degree. C. Silane gas is used to form a non-doped layer and about 1% of diborane or phosphine gas may be added to form a p-type or an n-type layer, respectively. The glow discharge is produced by a high frequency voltage applied to electrodes in the vacuum vessel but a direct current discharge may be used initially to provide improved adhesion of the layer. When the plate is heated above the crystallization temperature of the a-Si layer, heavy metal impurities are gettered from the single crystal.