Silane and germane plasma diagnostics for depositing photosensitive a-SiGe:H films

Highly photosensitive a-SiGe:H films with a light-to-dark conductivity ratio of 8*10³ and an optical bandgap of 1.40 eV have been produced by RF glow discharge using hydrogen dilution of SiH₄ and GeH₄ mixed gas plasma. The critical role of hydrogen dilution in GeH₄ containing plasmas is to suppress the gas-phase polymerization and promote the incorporation of Ge into the film. It is observed that inelastic laser light scattering of the RF plasma is a sensitive method for monitoring the onset of the gas-phase polymerization. In situ coherent anti-Stokes Raman spectroscopy measurements have shown that the dissociation rate of GeH₄ is a factor of three larger than that of SiH₄.