Controlling Fermi level pinning in near-surface InAs quantum wells

Hybrid superconductor-semiconductor heterostructures are a promising platform for quantum devices based on mesoscopic and topological superconductivity. In these structures, semiconductor must be in close proximity to superconductor form an ohmic contact. This can accommodated narrow band gap semiconductors such as InAs, where the surface Fermi level is positioned conduction band. this work, we study structural properties of near-surface InAs wells find that morphology closely connected low-temperature transport, electron mobility highly sensitive growth temperature underlying graded buffer layer. By introducing In$_{0.81}$Al$_{0.19}$As capping layer, show modify pinning within first nanometer thin film. Experimental measurements strong agreement with Schr\"odinger-Poisson calculations density, suggesting energy In$_{0.81}$Ga$_{0.19}$As pinned \SI{40}{\milli eV} \SI{309}{\milli above respectively.