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A detailed understanding of the material properties that affect the splitting between the two low-lying valley states in Si/SiGe heterostructures will be increasingly important as the number of spin qubits is increased. Scanning gate microscopy has been proposed as a method to measure the spatial variation of the valley splitting as a tip-induced dot is moved around in the plane of the Si quantum well. We develop a simulation using an electrostatic model of the scanning gate microscope tip and the overlapping gate structure combined with an approximate solution to the three-dimensional Schrödinger–Poisson equation in the device stack. Using this simulation, we show that a tip-induced quantum dot formed near the source and drain electrodes can be adiabatically moved to a region far from the gate electrodes. We argue that by spatially translating the tip-induced dot across a defect in the Si/SiGe interface, changes in valley splitting can be detected. [ABSTRACT FROM AUTHOR]

Gate-tunable high-mobility InSb/In1-xAlxSb quantum wells (QWs) grown on GaAs substrates are reported. The QW two-dimensional electron gas (2DEG) channel mobility in excess of 200 000 cm²/V s is measured at T = 1.8 K. In asymmetrically remote-doped samples with an HfO2 gate dielectric formed by atomic layer deposition, parallel conduction is eliminated and complete 2DEG channel depletion is reached with minimal hysteresis in gate bias response of the 2DEG electron density. The integer quantum Hall effect with Landau level filling factor down to 1 is observed. A high-transparency non-alloyed Ohmic contact to the 2DEG with contact resistance below 1 Ω·mm is achieved at 1.8 K. [ABSTRACT FROM AUTHOR]