A reactor for the dual sided deposition of thin-film semiconductor material layers in the approximate thickness range of less than 1 micron to 100 microns on two surfaces of a plurality of wafers carried on a batch susceptor, said batch susceptor having a window frame structure allowing access to said two surfaces of said plurality of wafers for dual sided deposition on said two surfaces of said plurality of wafers, said reactor comprising a gas flow chamber having a tapered gas flow space between an interior wall of said chamber and said susceptor to improve the deposition uniformity across each wafer and from wafer to wafer, a plurality of shelving slots for positioning said interior wall of said chamber in shelving positions, said deposition of thin film semiconductor material on a wafer is an epitaxial thin film monocrystalline silicon deposition and trichlorosilane is used as the precursor for thin film monocrystalline silicon deposition.