First-principles studies of tunneling properties of Al/Si and CoSi₂/Si junctions for novel silicon-based merged-element transmons

We present first-principles calculations of Schottky barrier heights (SBHs) at interfaces relevant for silicon-based merged-element transmon qubit devices. Focusing on Al(111)/Si(111) and CoSi₂(111)/Si(111), we consider various possible interfacial structures, for which we calculate the formation energies and Schottky barrier heights, and provide estimates of the Josephson critical currents based on the WKB tunneling formalism as implemented in the Tsu-Esaki model. We find that the formation energies and SBHs are very similar for all Al(111)/Si(111) structures, yet vary significantly for the CoSi₂(111)/Si(111) structures. We attribute this to the more covalent character of bonding at CoSi₂/Si, which leads to configurations with distinct atomic and electronic structure. Finally, our estimations show that these material interfaces are potentially capable of sustaining desired Josephson currents for novel merged-element transmons based on silicon fins.