Evaluation of Point Defect Complexes as Charge Noise Sources in Semiconductor Quantum Dot Qubits

Understanding the microscopic sources of charge noise in gate-defined semiconductor quantum dot qubits is instrumental to improving fabrication processes to minimize charge noise impacts on the performance of devices. Candidate objects causing charge noise include point defects and point defect complexes in various layers of the device, either above or adjacent to the confined electrons. These defects can form fluctuators with dynamic dipole moments and fluctuation frequencies that affect the qubits. Here, we use first principles atomistic simulations to evaluate a variety of point defect complexes in Si, SiGe, and silicon oxide as candidate fluctuators, by computing their stability, characteristic energy barriers, and dipole moments associated with atomic rearrangements. The variation of these characteristics with local strain, alloy composition, local chemical environment, and proximity to interfaces will be discussed. Both intrinsic and impurity-related defects are examined. Comparison with experiments allows identification of likely locations of these defects in devices. Our studies have identified several relevant defects for targeted mitigation during fabrication.