Comprehensive investigation of silicon surface passivation by a -Si:H and a -SiNx:H films

We studied the passivation properties and microstructure of a -Si:H and a -SiNx:H films deposited by PECVD on p-type and n-type CZ silicon wafers for solar cells with planar and texturized surfaces. Focusing on the comparison between radio frequency (13.56 MHz) and microwave (2.45 GHz) excited plasma deposition, a systematic variation of the precursor gas flow ratio [NH3]/[SiH4] from the range suitable for the antireflection coating of solar cells (refractive index ~ 2) up to a -Si:H, followed by a variation of the deposition as well as post-deposition temperature between 150 and 400 °C was carried out. For all wafers and wafer surface structures, very low effective surface recombination velocities were achieved in the stoichiometry transition range between a -SiNx:H and a -Si:H. Additional improvement of the surface passivation by a -Si:H was achieved by post-deposition annealing in N2 ambient. A correlation of this behavior to the microstructure of the passivation films is discussed for both plasma modes using measurements of the atomic bond densities and hydrogen content by means of the Fourier-transform infrared spectroscopy. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.