Detailed investigation of the structural and passivation properties of silicon oxynitrides for silicon solar cells

Abstract

We investigated the structural and passivation properties of hydrogenated amorphous silicon oxynitrides (a ‐SiOxNy:H) prepared by plasma enhanced chemical vapor deposition. Using energy dispersive X‐ray analysis and X‐ray photoelectron spectroscopy, we determined the stoichiometry x = [O]/[Si] and y = [N]/[Si] in the whole range extending from a ‐Si:H (x, y =0) to SiO2 (x ∼2, y ∼0). To analyze the thermal stability, test samples were subjected to high temperature firing in the range 850 to 950 °C. Charge carrier lifetime measurements revealed that Si‐rich a ‐SiOxNy:H feature excellent surface passivation on p‐type CZ silicon in the as‐deposited state. After firing, a ‐SiOx/a ‐SiNy:H stacks with near‐stoichiometric a ‐SiOx showed an outstanding thermal stability. A fine tracing of the density and spectral position of the Si‐O‐Si stretching vibration by means of the Fourier transform infrared spectroscopy revealed valuable information on the incorporation of oxygen and nitrogen atoms during deposition. Accordingly, we found that a high density of Si‐O‐Si bonds approaching the characteristic frequencies of thermal SiO2 and silica (1075 to 1080 cm–1) is clearly correlated to the interface passivation quality. Due to hydrogen migration from an a ‐SiNy:H cap layer induced by firing, the a ‐SiO2/a ‐SiNy:H system feature passivation properties close to thermally grown silicon oxide (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural properties of Si/SiO2 nanostructures grown by decomposition of substoichiometric SiOxNy layers for photovoltaic applications

“…For N 0 > 4, the [O]/[Si] ratio saturates to [O]/[Si] ≈ 2.0, corresponding to stoichiometric SiO 2 . This trend was also confirmed by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy 24. Slightly higher [O]/[Si] ratios than 2 are explained by the incorporation of interstitial oxygen 25.…”

“…Slightly higher [O]/[Si] ratios than 2 are explained by the incorporation of interstitial oxygen 25. Nitrogen is also incorporated into the SiO x N y films with increasing N 0 , but with a smaller amount than oxygen (by a factor of 5–10) 24. In addition, the nitrogen incorporation decreases with N 0 > 5.…”

Improved passivation effect at the amorphous/crystalline silicon interface due to ultrathin SiOx layers pre-formed in chemical solutions

“…[3][4][5] Hydrogenated amorphous silicon oxynitrides (a-SiO x N y :H) layer has also been proven to feature excellent surface passivation effect, offering a potential low cost substitute. 6) Moreover, pre-treatment of c-Si surface with hydrogen plasma prior to the deposition of a-Si:H layers and an amorphous SiN x (a-SiN x ) interlayer between c-Si and a-Si:H layers are also effective in obtaining abrupt c-Si/a-Si:H interfaces. 7,8) Silicon dioxide (SiO 2 ) is widely used as a surface passivation layer in semiconductor devices and crystalline silicon solar cells.…”

In Situ Process to Form Passivated Tunneling Oxides for Front-Surface Field in Rear-Emitter Silicon Heterojunction Solar Cells

“…This drawback can be addressed by employing wider bandgap materials, such as μc-Si:H and silicon tunneling oxide stacks, − as alternatives to the conventional a-Si:H stacks. , To form the wider bandgap-passivated silicon tunnel oxide, various methods have been investigated, such as wet and thermal oxidation and plasma-enhanced chemical vapor deposition (PECVD). Among these, the wet and thermal oxidation method exhibits disadvantages with respect to thickness control and the large valence-band offset at the heterointerface owing to the exceedingly large optical bandgap (∼9 eV), , in addition to a high processing temperature, which can cause wafer bending and entail high processing expenses. The devices based on the passivated silicon oxide deposited via PECVD suffer from a high series resistance, resulting in a low FF .…”