  Candidate systems for topologically-protected qubits include two-dimensional
electron gases (2DEGs) based on heterostructures exhibiting a strong spin-orbit
interaction (SOI) and superconductivity via the proximity effect. For InAs- or
InSb-based materials, the need to form shallow quantum wells to create a
hard-gapped $p$-wave superconducting state often subjects them to
fabrication-induced damage, limiting their mobility. Here we examine scattering
mechanisms in processed InAs 2DEG quantum wells and demonstrate a means of
increasing their mobility via repairing the semiconductor-dielectric interface.
Passivation of charged impurity states with an argon-hydrogen plasma results in
a significant increase in the measured mobility and reduction in its variance
relative to untreated samples, up to 45300 cm$^2$/(V s) in a 10 nm deep quantum
well.
