Enhanced Nanoscale Ge Concentration Oscillations in Si/SiGe Quantum Well through Controlled Segregation.

The integration of electron spin qubits on Si/SiGe heterostructures requires precise control of valley splitting associated with conduction band degeneracy. This can be achieved by introducing nanoscale oscillating Ge concentration profiles, known as Wiggle Wells. However, the intermixing and segregation of Ge during growth have hindered their realization. We report the growth of Si/SiGe heterostructures with clear nanoscale composition modulation within the quantum well using molecular beam epitaxy. By oscillation of the growth temperature, Ge segregation is suppressed, achieving a Ge concentration modulation of 30%/nm, an order of magnitude higher than prior results. Tight-binding simulations suggest that Wiggle Well heterostructures with sharp compositional transitions significantly enhance valley splitting, yielding average values exceeding 200 μeV, with energy levels well separated from 0 μeV. Hence, Wiggle Wells are a promising approach for Si-based electronic qubits.