PROPERTIES OF HYDROGENATED AMORPHOUS-SILICON CARBIDE FILMS PREPARED BY A SEPARATELY EXCITED PLASMA CVD METHOD

In order to prepare high-quality hydrogenated amorphous silicon carbid e (a-SixC1-x:H) films with a wide band Sap, we propose use of a separa tely excited plasma CVD (SEPCVD) system composed of two independent pl asma chambers and one deposition chamber. This method enables control of methane and silane plasmas independently. The optical and electrica l properties and structure of a-SixC1-x:H films prepared by the SEPCVD method were evaluated with visible-ultraviolet absorption spectroscop y, infrared transmission spectroscopy, x-ray photoelectron spectroscop y and measurements of the photo- and dark conductivities. The carbon c ontent and the optical band gap increased with increasing the ri power on both the methane side and the silane side. a-SixC1-x films with a carbon content above 0.6 and an optical band gap above 2.8 eV could be prepared by the SEPCVD method even though hydrogen-diluted gas was us ed. The SEPCVD method proved useful in preparing a-SixC1-x:H films wit h a wide gap. Both fourfold-coordinated carbon atoms and threefold-coo rdinated carbon atoms existed in films with carbon content from 0.5 to 0.6. However, the atomic percentage of threefold-coordinated carbon i n films prepared by the SEPCVD method is smaller than that obtained by the conventional method. [SiH2]/[SiH] was 0.1-0.3 and increased with increasing rf power. [SiHpi]/[Si] and [CH pi]/[C] decreased with incre asing rf power on the methane side, but they were not dependent on the ri power on the silane side. For a-SixC1-x:H films with an optical ba nd gap between 1.8 eV and 2.0 eV, the photoconductivity and the photos ensitivity were 10(-4) S Cm-1 and 10(6) respectively, and a-SixC1-x:H films with high photoconductivity could be prepared. However, the phot oconductivity of the a-SixC1-x:H films with an optical band gap above 2.2 eV was about 10(-10) S cm(-1).