Effective surface passivation of p-type crystalline silicon with silicon oxides formed by light-induced anodisation

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Electronic surface passivation of p-type crystalline silicon by anodic silicon dioxide (SiO2) was investigated. The anodic SiO2 was grown by light-induced anodisation (LIA) in diluted sulphuric acid at room temperature, a process that is significantly less-expensive than thermal oxidation which is widely-used in silicon solar cell fabrication. After annealing in oxygen and then forming gas at 400°C for 30min, the effective minority carrier lifetime of 3–5Ωcm, boron-doped Czochralski silicon wafers with a phosphorus-doped 80Ω/□ emitter and a LIA anodic SiO2 formed on the p-type surface was increased by two orders of magnitude to 150μs. Capacitance–voltage measurements demonstrated a very low positive charge density of 3.4×1011cm−2 and a moderate density of interface states of 6×1011eV−1cm−2. This corresponded to a silicon surface recombination velocity of 62cms−1, which is comparable with values reported for other anodic SiO2 films, which required higher temperatures and longer growth times, and significantly lower than oxides grown by chemical vapour deposition techniques. Additionally, a very low leakage current density of 3.5×10−10 and 1.6×10−9Acm−2 at 1 and −1V, respectively, was measured for LIA SiO2 suggesting its potential application as insulation layer in IBC solar cells and a barrier for potential induced degradation.