Abstract: A hot wire chemical vapor deposition apparatus for use in depositing thin films such as amorphous or epitaxial silicon upon a surface of a wafer or substrate by cracking a source or precursor gas such as silane. The apparatus includes a vacuum chamber and a source of precursor gas operable to inject the precursor gas into the chamber. The HWCVD apparatus also includes a heater with a support surface exposed to the deposition chamber, and the heater is operable to heat a substrate positioned upon the support surface. The apparatus includes a catalytic decomposition assembly with a filament positioned between the heater and the precursor gas inlet for selectively passing a current through the filament to resistively heat material of the filament. The filament material may be carbide such as tantalum carbide, which may be coated on a graphite core.