Silicon-Germanium-Boron Ternary Amorphous Alloy

Highly conductive ternary amorphous films are prepared by thermal decomposition of silane-germane-diborane mixtures in a low-pressure furnace at 500°C. The conductivity of the amorphous silicon-germanium-borom alloy exceeds the previously obtained limit for amorphous silicon, and increases with increasing germanium content. The d.c. conductivity and the Seebeck coefficient are measured at above room temperature. Measurements of the a.c. conductivity, optical absorption and E.S.R. are made at room temperature. The carrier transport is well described by a variable-range-hopping model. Evidences for a band model similar to that for the semimetal are proposed for the ternary amorphous alloy. In a higher germanium content film, the structure transforms into a microcrystalline one. The conductivity of microcrystalline silicon-germanium-boron alloy attains 103 Scm-1.