Over recent decades, surface-passivating properties of PECVD a-SiN_x:H have been investigated extensively. These properties depend on the number of fixed charges (Q_f) and interface density of states (D_it) and are in turn related to bulk and interface properties. In general, there is a positive correlation between Q_f and D_it, which have opposite effects on the surface-passivating properties. For an optimal effective surface passivation, an optimization is therefore necessary. Higher Q_f and D_it 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 Q_f at the interface on the passivating properties of a-SiN_x:H applied to completed solar cells was proven as well and confirmed by PC1D device simulations.

Chapter Contents:

• 11.1 Introduction
• 11.2 Surface-passivating properties related to bond structure
• 11.3 Effect of nitridation of the interface
• 11.4 Ab initio studies
• 11.5 Surface-passivating effect of a-SiNx: H layers onto different solar cell architectures
• 11.6 Conclusions
• References

Inspec keywords: electronic density of states; semiconductor-insulator boundaries; hydrogen; energy gap; ab initio calculations; density functional theory; solar cells; silicon; transmission electron microscopy; passivation; elemental semiconductors; electron energy loss spectra; silicon compounds; plasma materials processing

Other keywords: surface passivation; K-defects; fixed charges; bandgap density of states; TEM; ab initio DFT; hydrogenated amorphous silicon nitride; solar cell; SiN:H-Si; EELS; Si; plasma treatment

Subjects: Surface treatment and degradation in semiconductor technology; Other electron-surface impact phenomena; Density functional theory, local density approximation (condensed matter electronic structure); Electrical properties of metal-insulator-semiconductor structures; Solar cells and arrays; Elemental semiconductors; Surface states, surface band structure, surface electron density of states; Electrical properties of elemental semiconductors (thin films, low-dimensional and nanoscale structures); Surface treatment (semiconductor technology); Photoelectric conversion; solar cells and arrays; Plasma applications in manufacturing and materials processing; Ab initio calculations (condensed matter electronic structure); Metal-insulator-semiconductor structures; Electronic structure of elemental semiconductors (thin films, low dimensional and nanoscale structures)