  The valley splitting (VS) of a silicon quantum dot plays an important role
for the performance and scalability of silicon spin qubits. In this work we
investigate the VS of a SiGe/Si/SiGe heterostructure as a function of the size
and location of the silicon quantum dot. We use the effective mass approach to
describe a realistic system, which takes into account concentration
fluctuations at the Si/SiGe interfaces and also the interface roughness. We
predict that the size of the quantum dot is an important parameter for the
enhancement of the VS and it can also induce a transition between the
disorder-dominated to deterministic-enhanced regimes. Analyzing how the VS
changes when we move the quantum dot in a specific direction, we obtain that
the size of the quantum dot can be used to reduce the variability of the VS,
which is relevant for charge/spin shuttling.
