The electric field effectively repels minority carrier from the interface, resulting in the increase of minority carrier lifetime in the SiNW arrays. However, if a SiNW has perfect cylindrical symmetry, and Al2O3 with negative fixed charge is deposited on the surface uniformly, the electric field in the SiNW will be cancelled due to the symmetry of the electric field. Since in this case the effect of field effect passivation cannot be obtained, the effective lifetime will not be improved by annealing. To confirm the hypothesis, we tried to anneal the SiNW arrays with Al2O3 at 400°C. As a result, our SiNW samples also
showed improvement Caspase pathway of effective minority carrier lifetime, as well as a flat c-Si substrate passivated by Al2O3 layers, after annealing at 400°C. The τ eff was found to be 27 μs. From this result, we conclude that since this website the prepared SiNWs
do not have a perfect cylindrical symmetry, the effect of field effect passivation can be successfully obtained. Since negative charge density in the Al2O3 was increased by annealing at 400°C, the effective lifetime was also improved. Although τ eff of the SiNW arrays on the Si wafers were successfully obtained, we cannot consider these lifetimes as the lifetime of the SiNW region (τ SiNW) due to the influence of the Si wafers. Therefore, we tried to extract τ SiNW from τ eff using PC1D simulation. PC1D simulations revealed that τ eff was significantly influenced by the Si wafers. The calculated τ whole which is equivalent to the measured τ eff is 20 times higher than τ
SiNW, as shown in Figure 7. These simulations clearly indicate that the measured τ eff is completely different from τ SiNW. Figure 7 The calculated carrier lifetime. GPX6 Carrier lifetime in only a SiNW as a function of the carrier lifetime in the whole region by calculation based on Equation 5 and PC1D. We proposed a simple equation to extract τ SiNW from τ eff without numerical simulations. In the simulations of PC1D, minority carrier continuity equations were used. In general, the terms of drift, diffusion, recombination, and photogeneration have to be considered in the continuity equations. However, the terms of electric field and photogeneration can be eliminated. In μ-PCD measurement, a decay of excess carrier density is measured after stopping a laser irradiation. Therefore, photogeneration can be neglected. Although negative charge in Al2O3 can form electric field on the surface of SiNWs, the influence of the electric charge on excess carriers is limited only on the surface. Therefore, in this calculation, electric field was neglected for simplification. It was assumed that carriers were generated uniformly in the whole region because the carrier density remained alternated by time variation from the resulting PC1D.
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