CVD DIAMOND GROWTH ON GERMANIUM FOR IR WINDOW APPLICATIONS

We show that the production of adherent polycrystalline diamond films upon Ge substrates by chemical vapour deposition is problematical for three reasons: (a) the melting point of Ge is close to the optimum dia mond deposition temperature which leads to partial melting of the Ge s urface, retarding diamond nucleation, (b) there is no Ge carbide layer formed at the interface to bond the diamond to the Ge chemically and (c) there is a large thermal expansion mismatch between diamond and Ge , resulting in cracking and flaking off of the films. Barrier layers o f silicon dioxide, nitride or amorphous Si 1 mum thick prevent the Ge surface melting, but do not alleviate the expansion mismatch problem. The resulting three-layer sandwich crazes upon cooling, with the delam ination occurring at the Ge-barrier interface.