Outstanding surface passivation of low-resistivity single-crystalline p-silicon is reported using silicon nitride fabricated at low temperature (375 °C) in a remote plasma-enhanced chemical vapor deposition system. The effective surface recombination velocity Seff is determined as a function of the bulk injection level from light-biased photoconductance decay measurements. On polished as well as chemically textured silicon wafers we find that our remote plasma silicon nitride provides better surface passivation than the best high-temperature thermal oxides ever reported. For polished 1.5 and 0.7 Ω cm p-silicon wafers, record low Seff values of 4 and 20 cm/s, respectively, are presented.

In a recent letter [Lauinger et al., Appl. Phys. Lett. 68, 1232 (1996)] we have shown that record low effective surface recombination velocities Seff of 4 cm/s have been obtained at ISFH on low-resistivity (1 Ω cm) p-type crystalline silicon using microwave-excited remote plasma-enhanced chemical vapor deposition (RPECVD) of silicon nitride at low temperature (300–400 °C). As an important application, this technique allows a simple fabrication of rear-passivated high-efficiency silicon solar cells with monofacial or bifacial sensitivity. In this work, we present details of the required optimization of the PECVD parameters and a characterization of the resulting silicon nitride films. All deposition parameters are shown to strongly affect Seff as well as the stability of the films against the ultraviolet (UV) photons of terrestrial sunlight. A clear correlation between Seff and the film stoichiometry is observed, allowing a simple control and even a rough optimization of the surface passivation quality by measurements of the refractive index of the films. An optimum passivation and UV stability is obtained for silicon-rich silicon nitride films with a refractive index greater than 2.3.

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In this paper, the lowest ever reported effective surface recombination velocities Seff on typical p-type low-resistivity silicon solar cell substrates are presented. We obtain this surface passivation by means of remote plasma silicon nitride films fabricated at 375°C. On polished as well as on chemically textured silicon surfaces, the applied low-temperature passivation scheme is significantly superior to high-temperature passivation by state-of-the-art thermal oxides. On polished 1.5-Qcm p-Si wafers, an extremely low Seff value of 4 cm/s is obtained. Because of the enormous potential of these plasma silicon nitride films as passivation medium for the rear surface cells, we also investigate silicon nitride grid-covered p-Si surfaces as used by us cells. On such samples we measure spa Se, values as low as 135 cm/s.

Experimental evidence is presented that the effective surface recombination velocity (Seff) at p-silicon surfaces passivated by silicon nitride films (fabricated in a plasma-enhanced chemical vapor deposition system) shows an injection-level dependence similar to the behavior of thermally oxidized silicon surfaces. Using the microwave-detected photoconductance decay method, injection-level dependent Seff measurements were taken on nitride-passivated p-silicon wafers of different resistivities (1.5–3000 Ω cm). The obtained Seff values also show that for low-resistivity substrates (≤2 Ω cm), nitride passivation is as effective as conventional oxide passivation (and even superior at low injection levels) and furthermore offers the advantage of a less pronounced injection-level dependence.

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