Characterizing Valley Splitting in Si/SiGe Quantum Devices Using a Scanning Gate Microscope Tip-Induced Quantum Dot*

            A solid understanding of the materials properties that affect the splitting between the two low-lying valley states in Si/SiGe heterostructures will be increasingly important as the number of qubits is increased [1]. Scanning gate microscopy (SGM) has been proposed as a method to measure the spatial variation of the valley energies as the tip-induced dot is moved around in the plane of the Si quantum well [2]. Utilizing domain decomposition techniques, an electrostatic model of the SGM tip bias and the 3D overlapping gate structure can be combined with an approximate solution to the 3D Schrödinger-Poisson equation [3]. With these simulation tools, we show that a tip-induced quantum dot formed near source and drain electrodes can be adiabatically moved to a region far from the gate electrodes. By spatially translating the tip-induced dot across a defect in the Si/SiGe interface, changes in valley energy splitting can be detected.

 

[1] Burkard et al., Phys. Rev. B 94, 195305 (2016)

[2] Shim et al., Appl. Phys. Lett. 114, 152105 (2019)

[3] Anderson et al., J. Comput. Phys. 228, 4745 (2009)