Over recent decades, surface-passivating properties of PECVD a-SiNx:H have been investigated extensively. These properties depend on the number of fixed charges (Qf) and interface density of states (Dit) and are in turn related to bulk and interface properties. In general, there is a positive correlation between Qf and Dit, which have opposite effects on the surface-passivating properties. For an optimal effective surface passivation, an optimization is therefore necessary. Higher Qf and Dit are found to correspond to a higher and deeper insertion of N in c-Si thereby increasing the concentration of these defects. This insertion is related to NH3 flow and temperature during plasma treatment. This technique for forming defect layers has been experimentally validated by EELS as well as high resolution TEM. MD simulation and ab initio DFT studies demonstrated the formation of defects and higher DOS in the bandgap for the same layer composition. Introduction of hydrogen was simulated with DFT as well and showed a lower DOS in the bandgap resulting in a better surface passivation. The effect of Qf at the interface on the passivating properties of a-SiNx:H applied to completed solar cells was proven as well and confirmed by PC1D device simulations.
Hydrogenated amorphous silicon nitride (a-SiNx:H) as surface passivation layer, Page 1 of 2
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