Characterizing Spurious Dots due to Random-Alloy Disorder in Si/SiGe Heterostructures

While semiconducting qubit design and fabrication have grown more sophisticated over the decades, device uniformity remains challenging, limiting the ability to scale up to large operations. Introducing small concentrations of germanium to the quantum well in Si/SiGe heterostructures lifts degeneracy between the low-lying states in the silicon conduction band, offering a solution to the valley-splitting problem, but also introducing random-alloy disorder [Losert, 2023]. In this work, we find that random-alloy disorder disrupts device uniformity through the emergence of spurious dots. We solve systems with physically realistic alloy disorder using a 2D effective-mass Hamiltonian with coupling between the z valleys and observe disorder-induced dots with orbital energy scales ~0.3-1.0 meV in the limit of no lateral electrostatic confinement. This behavior persists in the limit of electrostatic confinement on the order of typical experimental systems ~2 meV in the form of shifted dot position, deformed dot shape, and the formation of spurious dots away from the electrostatic potential minimum. In both limits, the disorder is correlated with Ge concentration. This new understanding of spurious dots illuminates infidelity seen in current devices and will inform next-generation devices.