Tracking interfacial disorder in SiGe qubit material

Theory predicts quantum dot electrons interact with interface atomic-scale disorder, perturbing energetics, creating new potentially useful states, and adding complexity that could dictate viability of some future qubit technologies. Although profoundly impactful, the predictions are challenging to test, since relevant structures are difficult to measure and correlate with qubit behavior. We've measured atomic step disorder at Si/SiGe interfaces using scanning tunneling microscopy coupled to an epitaxial growth tool. We report a counterintuitive evolution of roughness and step spatial correlations during growth. The results are meaningful toward elucidating structure-function relationships in SiGe QDs.