Optical properties of PECVD and UVCVD SiN/sub x/:H antireflection coatings for silicon solar cells

Abstract

A complete study of the optical properties has been achieved for hydrogenated silicon nitride SiN,:H obtained by either Low Frequency (40kHz) Plasma Enhanced Chemical Vapour Deposition (LF-PECVD) or by another low temperature deposition technique: UltraViolet photoassisted CVD (UVCVD). Spectroscopic ellipsometry measurements were carried out on a large number of samples. The results were gathered in a data library in order to compute the wavelength-dependant reflection, absorption and transmission coefficients through the layers. Different optical behaviors were observed according to the deposition technique, with stronger absorption and hence smaller optical gaps for UVCVD films. This is believed to be due to the formation in the SIN, matrix of amorphous silicon (a-Si) clusters, which seem to be much bigger than those obtained in PECVD layers.

Study of the composition of hydrogenated silicon nitride SiNx:H for efficient surface and bulk passivation of silicon

“…When comparing SiN obtained with different deposition techniques, the complete complex optical index N = n + ik should be taken into account. Indeed, the extinction coefficient k at low wavelengths gives reliable information on the Si-content of the SiN layer, as we have already suggested elsewhere [43,44].…”

Hydrogenated Silicon Nitride SiNx:H Deposited by Dielectric Barrier Discharge for Photovoltaics

“…As the refractive index increases with the Si‐content of the thin film (Figures 4b and ), the corresponding increase of the extinction coefficient is attributed to a larger concentration of strongly absorbing Si–Si bonds and Si° dangling bonds . However, Figure shows that two SiN films with identical refractive index can exhibit different extinction coefficients.…”

“…The value of n is usually measured for λ = 634 nm because it corresponds to region of the solar spectrum for which silicon solar cells generate most charge carriers. The extinction coefficient is measured at 430 nm because it is the lowest wavelength available from our ellipsometric data, and the absorption in the coating is the highest for low wavelengths . In addition, reflectivity measurements operating with an integrating sphere were carried out in the 300–1200 nm wavelength range.…”

“…The higher values of k for silicon‐rich SiN films are attributed to the increase of the number of strongly absorbing Si–Si bonds and Si° dangling bonds within the SiN layer . Thus, the absorption ( A ) within the ARC must be taken into account for high refractive index layers (typically n > 2.1).…”

Advanced optical modelling of dynamically deposited silicon nitride layers

“…It has been used to characterize PECVD SiN x films in several studies since the development of the Tauc-Lorentz oscillator formalism. [8][9][10][11][12][13][14][15][16] Some of the studies were performed on films grown by static deposition (substrate stationary under the plasma source); and other studies included dynamically deposited (substrate moving in one direction under the plasma source) SiN x layers.…”