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

The modification of surface reactions with an inert gas plasma treatment method has been investigated for the first time in order to improve the properties of a-Si:H for solar cells. The deposition of a thin a-Si:H layer and exposure to inert gas plasma such as He, Ar or Xe were repeated by using RF plasma CVD at a substrate temperature of 200 °C. It has been found that the hydrogen content (Ch) can be controlled in a wide range from about 18 atomic% to about 35 atomic%, although it is a hydrogen-free process. Experimental results show that the change in Ch of a-Si:H films is mainly determined by the decrease in Ch of the treated a-Si:H surface and the increase in Ch of the a-Si:H deposited on the treated surface. Furthermore, the plasma treatment probably promotes the surface reaction, which reduces S1H2/S1H and Ch- Consequently, wide-gap (1.64 eV by ( a h v )1/3 versus h v plots, 1.75–1.85 eV by Tauc's plot) a-Si:H films with high stabilized photoconductivity (> 10−5 Ω−1cm−1 under AM-1, 100 mW/cm2 irradiation) have been obtained by the inert gas plasma treatment method.