Characterizing Charged Defects in Oxide-on-Silicon using Kelvin Probe Force Microscopy

While silicon-based quantum dot qubits are a promising platform for quantum computing, due to their long coherence times, charge noise from oxide layers below the gate electrodes hinders critical improvements in qubit operations. To characterize the microscopic origin of charge noise in these gate oxides, we perform Kelvin Probe Force Microscopy (KPFM) measurements on a thin aluminum-oxide layer grown atop silicon dioxide and bulk silicon. These experiments reveal defects in the oxide that exchange charges with the AFM tip when its bias voltage is swept. By repeating such scans while rastering the tip over the sample, and comparing them to electrostatic simulations of the tip and sample, we can identify the depths of the charged defects. We further investigate the binding energies of the defects, making use of the charging voltages from our experiments. These results will be useful for understanding and potentially improving qubit gate operations.