  Quantum computers have the potential to efficiently solve problems in
logistics, drug and material design, finance, and cybersecurity. However,
millions of qubits will be necessary for correcting inevitable errors in
quantum operations. In this scenario, electron spins in gate-defined silicon
quantum dots are strong contenders for encoding qubits, leveraging the
microelectronics industry know-how for fabricating densely populated chips with
nanoscale electrodes. The sophisticated material combinations used in
commercially manufactured transistors, however, will have a very different
impact on the fragile qubits. We review here some key properties of the
materials that have a direct impact on qubit performance and variability.
