Low Carbon Contamination of Epitaxial Germanium Films Produced by Pyrolysis of Alkyl Germanium Compounds

Thin films of Ge produced by the pyrolysis of alkyl germanium tetramethyl germanium and tetraethyl germanium compounds have been studied for their rates of deposition, crystallinity, and carbon contamination. The pyrolysis reaction has been found to be of first order, and the activation energies have been found to vary with concentration of the alkyl germanium compound between the limits of 25-30. kcal/mole for both tetramethyl and tetraethyl germanium. The morphology and crystallinity of the films vary with the chemical and crystalline structure of the substrate. Good quality and uniform films are produced on monocrystalline germanium substrates preetched in situ with HC1 gas. The carbon contamination is found to be strongly dependent on the substrate material, and it varies between 25 ppm for germanium and 200-50,000 ppm for tungsten substrates.