Mechanism of carrier transport through a silicon-oxide layer for 〈indium-tin-oxide/silicon-oxide/silicon〉 solar cells

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Abstract
The mechanism of carrier transport through a thin silicon‐oxide layer for 〈spray‐deposited indium‐tin‐oxide (ITO)/silicon‐oxide/Si〉 solar cells has been studied by measurements of the dark current density as a function of the thickness of the silicon‐oxide layer, together with the observation of transmission electron micrographs. Cross‐sectional transmission electron micrography shows that a uniform silicon‐oxide layer with the thickness of ∼2 nm is present between ITO and Si when the ITO film is deposited on a flat Si(100) surface at 450 °C. The dark current density under a depletion condition strongly depends on the thickness of the silicon‐oxide layer. It is concluded from these results that quantum mechanical tunneling is the dominant mechanism for the charge carrier transport through the silicon‐oxide layer. On the other hand, when the ITO film is deposited on a mat‐textured Si surface at the same temperature, a nonuniform silicon‐oxide layer is formed, with ITO penetrating into the silicon‐oxide layer in the top and valley regions of the pyramidal structure. By raising the deposition temperature of the ITO film on the flat Si(100) surface to 500 °C, the silicon‐oxide layer becomes also nonuniform. For these diodes with the nonuniform silicon‐oxide layer, the carrier transfer probability is less dependent on the thickness of the silicon‐oxide layer, leading to the conclusion that minute channels of ITO are present in the silicon‐oxide layer and charge...