| Popis: |
The temperature dependence of the open-circuit photovoltage, Voc, has been studied for n-type silicon electrodes immersed in a methanol solution, and the major components of the dark current and the barrier height have been determined. It was found that the minority carrier dark current is dominant at room temperature, while the majority carrier dark current is dominant at ~ −75 °C. Analysis of the n value showed that, for the case of a highly doped silicon, e.g. with a donor density of 3.5 × 1018 cm−3, the recombination rate in the depletion layer and at the surface is negligibly small, and an additional photovoltage of ~ 20 mV is obtained from the presence of the Helmholtz layer, leading to a high photovoltage. On the other hand, for the n-Si electrodes of low donor density 5 × 1015 cm−3, the recombination rate in the depletion layer increases as the depletion layer width increases. The effective barrier height in the 3.5 × 1018 cm−3 silicon is ~ 150 mV smaller than that for the 5 × 1015 cm−3 silicon due partly to the potential drop across the Helmholtz layer (~ 50 mV) and mainly to majority carrier tunnelling through the thin depletion layer (~ 100 mV). |
