Understanding and mitigating resistive losses in fired passivating contacts: role of the interfaces and optimization of the thermal budget

We study p-type passivating contacts based on SiC_x formed via a rapid thermal processing step, using conditions compatible with the firing used to sinter screen-printed metallization pastes in industry. Firstly, we separate the contributions of the two interfaces to the contact resistivity (wafer/contact and contact/metal), identifying tunnelling at the wafer interface as the main contribution. We then investigate the dependence of contact resistivity and sheet resistance of the SiC_x layer on the concentration of active dopants and we propose strategies to reduce both resistances by increasing the thermal budget applied during firing. Lastly, we discuss potentials and limitations of implementing the investigated stacks as rear side contacts of p-type devices with localized metallization, and we show that an oxide layer that can withstand high thermal budgets is the key factor for obtaining high passivation quality and good electrical properties at the same time. The results obtained with an oxide based on N₂O plasma oxidation show that this layer is a promising candidate for such an application.