Local laser-induced solid-phase recrystallization of phosphorus-implanted Si/SiGe heterostructures for contacts below 4.2 K

Si/SiGe heterostructures are of high interest for high-mobility transistor and qubit applications, specifically for operations below $4.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. 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 monolayer 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 $4.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and obtain values similar or superior to that of a globally annealed reference sample. This highlights the usefulness of laser-based annealing to take full advantage of high-performance Si/SiGe heterostructures.