Impact of interface traps on charge noise, mobility and percolation density in Ge/SiGe heterostructures

TL;DR

This study investigates how interface traps at the semiconductor-oxide boundary in Ge/SiGe heterostructures influence charge noise, mobility, and percolation density, which are critical for optimizing spin qubit performance.

Contribution

It identifies the semiconductor-oxide interface traps as the main source of charge noise and demonstrates how gate voltages affect trap filling and device stability.

Findings

Interface traps cause hysteresis and charge noise in Ge/SiGe devices.

Negative gate voltages increase trap filling and electrostatic disorder.

Interface quality is crucial for spin qubit coherence.

Abstract

Hole spins in Ge/SiGe heterostructure quantum dots have emerged as promising qubits for quantum computation. The strong spin-orbit coupling (SOC), characteristic of heavy-hole states in Ge, enables fast and all-electrical qubit control. However, SOC also increases the susceptibility of spin qubits to charge noise. While qubit coherence can be significantly improved by operating at sweet spots with reduced hyperfine or charge noise sensitivity, the latter ultimately limits coherence, underlining the importance of understanding and reducing charge noise at its source. In this work, we study the voltage-induced hysteresis commonly observed in SiGe-based quantum devices and show that the dominant charge fluctuators are localized at the semiconductor-oxide interface. By applying increasingly negative gate voltages to Hall bar and quantum dot devices, we investigate how the hysteretic filling of interface traps impacts transport metrics and charge noise. We find that the gate-induced accumulation and trapping of charge at the SiGe-oxide interface leads to an increased electrostatic disorder, as probed by transport measurements, as well as the activation of low-frequency relaxation dynamics, resulting in slow drifts and increased charge noise levels. Our results highlight the importance of a conservative device tuning strategy and reveal the critical role of the semiconductor-oxide interface in SiGe heterostructures for spin qubit applications.