Measurement of Contact Resistivity In Symmetric Polycrystalline Si/SiOx/Monocrystalline Si Test Structures Using Variable Light Illumination

While different methods exist to determine the contact resistivity in semiconductor devices, these methods are limited to measurement of the majority carrier contacts. The measurement of p- or n-type contacts on n- or p-type crystalline silicon, respectively, is challenging due to the blocking diode formed by the p–n junction. In this article, we address this problem for tunneling oxide passivating contacts used in high-efficiency Si solar cells. We propose a universal method to extract contact resistivity on symmetric test structures with polycrystalline silicon on SiO_x (poly-Si/SiO_x) passivating contacts under illumination, both for p–n and high–low-junction passivated contacts. In this method, we demonstrate that the total contact resistance of each cell grid finger to the base wafer is governed by its effective contact area, defined by the transfer length extending from both sides of the finger. Therefore, the grid contact resistance of a poly-Si contact depends on the ratio of the doped poly-Si sheet resistance to the tunneling contact resistivity.