Defect Identification of Atomic Layer Deposited Aluminum Oxide using Kelvin Probe Force Microscopy

Kelvin Probe Force Microscopy (KPFM) measurements combined with density functional theory (DFT) calculations are used to identify individual charged defects in an amorphous aluminum oxide layer grown via atomic layer deposition (ALD) atop bulk silicon. Charged defects in the oxide, especially those supporting multiple charge states, are an important source of charge noise in silicon-based quantum dot qubits, and thus defect characterization and identification are key to noise mitigation. Local variations in the work function found using KPFM reveal a high density of charged defects in the aluminum oxide layer. Sweeping the AFM tip-to-sample bias induces charging and discharging events near the surface, allowing us to probe the defects' different charge states. With the aid of electrostatic simulations, we extract the charging and discharging energies as a function of voltage bias. The sign and magnitude of a charge state can also be determined from KPFM measurements. Combining information about the charging energies with the sign and magnitude of the charged states allows us to identify individual defects with high confidence, by comparison with DFT calculations. This work represents a unique and novel approach to imaging and identifying point defect distributions down to individual defects and can even distinguish multiple overlapping defects in some cases. This work was partially performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.