High quality amorphous silicon films prepared by atmospheric-pressure photo-CVD

The authors prepared undoped a-Si:H films by an atmospheric-pressure mercury-sensitized photo-CVD (chemical vapor deposition) process. This technique made it possible to reduce the impurity concentration and to obtain high-quality films. The maximum deposition rate of 45 A/min was obtained by optimizing the mercury reservoir temperature and the flow rate of SiH₄. The maximum ratio of photoconductivity (AM-1, 100 mW/cm²) to dark conductivity was 6*10⁶ with an optical bandgap of 1.78 eV. The concentration of oxygen in the films prepared by this growth technique was 2*10¹⁸ cm^-3, which is one order of magnitude lower than that of films grown by low-pressure photo-CVD. At an initial stage, an efficiency of 9.1% has been obtained for a solar cell with the i layer deposited by atmospheric-pressure photo-CVD.