INTERFACIAL PROCESSES IN THE PD A-GE-H SYSTEM

The kinetics of phase transformations has been studied in a two-layer structure of Pd/a-Ge:H after vacuum annealing at temperatures from 180 to 500-degrees-C. The a-Ge:H was deposited at 250-degrees-C on both c -Si and cleaved NaCl substrates in an RF glow discharge from a GeH4/H- 2 mixture. It was found that, similarly to the Pd/c-Ge and the Pd/a-Ge (e-gun deposited) systems, in the case of 0.15-0.2 mum Pd/0.6-1.0 mum a-Ge:H interfacial germanides formed first through the production of Pd2Ge (plus a small amount of PdGe), and then PdGe was produced. The g rowth of both compounds was found to be diffusion-controlled. The nonr eacted a-Ge:H layer beneath the germanide overlayer crystallized at 40 0-500-degrees-C. A reverse sequence of germanides formation was reveal ed in the case of 50 nm Pd/30 nm a-Ge:H, studied by in situ heat treat ment in the TEM utilizing non-supported samples. The first germanide d etected was PdGe and then, as a result of PdGe and Ge reaction or the PdGe decomposition, Pd2Ge formed. The temperature dependence of the in cubation time before the first approximately 10 nm PdGe grains formed, followed an Arrhenius curve with an activation energy of 1.45 eV.