Extended Cox & Strack analysis for the contact resistance of planar samples with carrier-selective junctions on both sides

Abstract

We review the famous Cox & Strack equation that is commonly applied in contact resistance measurements of samples with a negligible contact resistance at the sample backside. We apply geometric interpretations to extend the Cox & Strack model a) to samples that have a non-negligible contact resistance not only on the front- but also on the back-side and b) to junctions with a buried contact resistance underneath a conductive layer. Case a) is for example a symmetric sample with a single material junction on both sample surfaces. Case b) could be a poly-Si/SiOx/c-Si or a-Si/c-Si hetero-junction. We compare our analytic treatment with rigorous finite-element simulations and find a relative agreement between 2.5 % and 36 % depending on the sample geometry and resistance values. We apply the method to analyze the contact resistance of lifetime samples with both-sided n+/n-type poly-Si junctions.