Effect of an interface step on the Valley Splitting in a Si/SiGe quantum dot*

Valley-orbit coupling, which is generally a complex quantity, is a key parameter for a Si quantum dot in determining its suitability for applications in quantum information processing. With Si conduction band valleys far apart in the First Brillouin Zone, valley-orbit coupling strength is sensitive to the interface roughness. One type of common roughness at interface is steps in Si composition. Using effective mass approximation, here we explore how the position of a step or steps at the interface affects the energy levels of an electron in a Si/SiGe quantum dot. We include higher-energy orbital levels, Umklapp processes, and Bloch states in our calculation. Our results show that the magnitude of valley splitting is mostly determined by the envelop function, and generally decreases when a step is introduced. The phase of the valley-orbit coupling is also affected by the step(s) through the envelope function.