  Si/SiGe heterostructures are of high interest for high mobility transistor
and qubit applications, specifically for operations below 4.2 K. In order to
optimize parameters such as charge mobility, built-in strain, electrostatic
disorder, charge noise and valley splitting, these heterostructures require Ge
concentration profiles close to mono-layer precision. Ohmic contacts to undoped
heterostructures are usually facilitated by a global annealing step activating
implanted dopants, but compromising the carefully engineered layer stack due to
atom diffusion and strain relaxation in the active device region. We
demonstrate a local laser-based annealing process for recrystallization of
ion-implanted contacts in SiGe, greatly reducing the thermal load on the active
device area. To quickly adapt this process to the constantly evolving
heterostructures, we deploy a calibration procedure based exclusively on
optical inspection at room-temperature. We measure the electron mobility and
contact resistance of laser annealed Hall bars at temperatures below 4.2 K and
obtain values similar or superior than that of a globally annealed reference
samples. This highlights the usefulness of laser-based annealing to take full
advantage of high-performance Si/SiGe heterostructures.
