Improvement in a-Si:H Properties by Inert Gas Plasma Treatment

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Abstract
Inert gas plasma treatment, using RF plasma chemical vapor deposition (CVD), has been investigated for the first time in order to improve a-Si:H properties through the modification of reactions at the growing surface. The deposition of a thin a-Si:H layer (6–150 Å) and exposure to inert gas plasma of He, Ar or Xe were repeated using RF plasma CVD at a substrate temperature of 200°C. It was found that the plasma treatment can be used to control the hydrogen content (C H) from about 18 at.% to about 35 at.%, although it is a hydrogen-free process. Experimental results indicate that the change in the C H of a-Si:H films is mainly determined by the decrease in the C H of the treated a-Si:H surface and the increase in the C H of the a-Si:H deposited on the treated surface. Furthermore, the inert gas plasma treatment probably promotes the surface reaction, which leads to a reduction of SiH2/SiH and C H. Consequently, high-quality a-Si:H films with a wide gap (1.64 eV determined from (αhν)1/3 versus hν plots, 1.75–1.85 eV determined from Tauc's plot), low SiH2/SiH (C H∼30 at.%, SiH2/SiH ∼0.1) and high stabilized σ ph (>10-5 Ω-1cm-1 under AM-1, 100 mW/cm2 irradiation) have been obtained by the inert gas plasma treatment method.